Memory Clobbered Before Allocated Block | Code For Game Developers – Anatomy Of A Memory Allocation 상위 62개 답변

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t-double.c (memory clobbered before allocated block)

t-double.c (memory clobbered before allocated block). Marc Glisse marc.glisse at inria.fr. Wed Feb 27 15:44:28 CET 2013.

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Misaddressing_Memory

Incrementing a pointer past the end of a block of allocated memory. This is similar to the array subscript problem. Nothing stops your code from using a …

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주제와 관련된 이미지 memory clobbered before allocated block

주제와 관련된 더 많은 사진을 참조하십시오 Code for Game Developers – Anatomy of a Memory Allocation. 댓글에서 더 많은 관련 이미지를 보거나 필요한 경우 더 많은 관련 기사를 볼 수 있습니다.

주제에 대한 기사 평가 memory clobbered before allocated block

• Author: Jorge Rodriguez
• Views: 조회수 11,213회
• Likes: 좋아요 293개
• Date Published: 2015. 8. 1.
• Video Url link: https://www.youtube.com/watch?v=c0g3S_2QxWM

Memory Clobbering Error

You are incrementing ptr , therefore changing the address that it points to. You can’t do that.

In your case, have a separate pointer, let’s say char * p = ptr and do your operations with p leaving ptr intact so you can free(ptr) later.

EDIT Taking a second look at your code, I found that you are doing ptr++ when you shouldn’t. You are accessing the characters in the array like ptr[i] , if you mess with the ptr pointer, you are changing the base address and accessing the characters with ptr[i] can lead (and will lead) to unexpected results.

If you simply remove that line ( ptr++ ) your code will magically work. If you want to explore the pointer concept and try another solution, your code could look something like this:

Whaddya mean I clobbered past the mem block?

Code:

Reserving 301445280 to 301445728 Alloced table at 301445216 Adding 1, 100 to 301445280 new items at 0 Size: 0 ==733== Invalid write of size 8 ==733== at 0x4009E6: insert (table.c:107) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B108 is 0 bytes inside a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1BC: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B109 is 0 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1C7: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10A is 1 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1D2: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10B is 2 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1B1: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10C is 3 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) Adding 2, 200 to 301445384 ==733== ==733== Invalid read of size 4 ==733== at 0x400A41: insert (table.c:118) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10C is 3 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid read of size 4 ==733== at 0x40124E: contains (table.c:413) ==733== by 0x400D21: delete (table.c:234) ==733== by 0x4007BE: main (public02.c:27) ==733== Address 0x11F7B108 is 0 bytes inside a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) Size: 1 table at 301445216 Items at 301445384

C Language, “memory clobbered before allocated block”…?

“memory clobbered before allocated block”…?

“memory clobbered before allocated block”…? Author Message Fredrik L?nnergre

#1 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

Greetings.

Greetings. I have a program that among other things utilizes a large array of structs,

which is frequently accessed throughout the program. However, when I try to

free() or realloc() that array (in order to resize it), it says what I typed

in the title…For now, I’m left with a known, substantial even though

infrequent memory leak.

I’ve run the program under gdb, but found nothing of real value there,

either before the “allocated block” nor in the structs in the array I’ve

looked into. I’ve also searched the ‘net for some info, but all I could find

was some pretty vague reference to “char subscripting” whatever that means.

I’ve also looked at the calloc(), memset() and malloc() calls that are used

with this array and some of the structs in it. Still no luck. The structs in

the array contain pointers (to strings, functions and other structs) as

well…

How can I find the source of this anomaly? What’s the best method here?

Since the program is over 100 kloc and this array used throughout it, I’m

afraid I can’t show any really good example here.

TIA,

Fredrik

Sun, 23 Mar 2003 03:00:00 GMT Robert Stankowi

#2 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

Fredrik, “Fredrik L?nnergren” schrieb:

Quote:

> Greetings. > I have a program that among other things utilizes a large array of structs,

> which is frequently accessed throughout the program. However, when I try to

> free() or realloc() that array (in order to resize it), it says what I typed

> in the title…For now, I’m left with a known, substantial even though

> infrequent memory leak.

> I’ve run the program under gdb, but found nothing of real value there,

> either before the “allocated block” nor in the structs in the array I’ve

> looked into. I’ve also searched the ‘net for some info, but all I could find

> was some pretty vague reference to “char subscripting” whatever that means.

> I’ve also looked at the calloc(), memset() and malloc() calls that are used

> with this array and some of the structs in it. Still no luck. The structs in

> the array contain pointers (to strings, functions and other structs) as

> well…

> How can I find the source of this anomaly? What’s the best method here?

> Since the program is over 100 kloc and this array used throughout it, I’m

> afraid I can’t show any really good example here.

> TIA,

> Fredrik

freeing it later would cause exactly the problem you describe.

just a thought – can it be that you are malloc()ing a zero size array somewhere?freeing it later would cause exactly the problem you describe. consider

void foo()

{

char *cPtr;

unsigned aSize=get_how_many_bytes_needed();

cPtr=malloc(aSize);

free(cPtr);

Quote: }

the free() will fail (most likely crash) if get_how_many_bytes_needed() returns

HTH Robert

the free() will fail (most likely crash) if get_how_many_bytes_needed() returnsHTH Robert – Hide quoted text – – Show quoted text – Quote: }

Sun, 23 Mar 2003 03:00:00 GMT Fredrik L?nnergre

#3 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Quote:

>Fredrik,

>Fredrik, *snip*

>just a thought – can it be that you are malloc()ing a zero size array

somewhere?

>freeing it later would cause exactly the problem you describe.

>consider

>void foo()

>{

> char *cPtr;

> unsigned aSize=get_how_many_bytes_needed();

> cPtr=malloc(aSize);

> free(cPtr);

>}

>the free() will fail (most likely crash) if get_how_many_bytes_needed()

returns

>0

>HTH Robert

But in the occasions when this happens the array is always allocated for and

populated by about 12000 elements. Could it be that one of the structs in a

struct in the array has been 0-malloc()ed? Is the behavior you describe

recursive into “members” so to speak?

Hmm…it’s possible, I’m not the only one coding on that…But in the occasions when this happens the array is always allocated for andpopulated by about 12000 elements. Could it be that one of the structs in astruct in the array has been 0-malloc()ed? Is the behavior you describerecursive into “members” so to speak? TIA,

Fredrik

Sun, 23 Mar 2003 03:00:00 GMT Dan P

#4 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

Quote:

>freeing it later would cause exactly the problem you describe.

>just a thought – can it be that you are malloc()ing a zero size array somewhere?>freeing it later would cause exactly the problem you describe. >consider

>void foo()

>{

> char *cPtr;

> unsigned aSize=get_how_many_bytes_needed();

> cPtr=malloc(aSize);

> free(cPtr);

>}

>the free() will fail (most likely crash) if get_how_many_bytes_needed() returns

>0

>HTH Robert

It doesn’t help because it’s pure bullshit! If the size of the space requested is zero, the behavior is

implementation-defined; the value returned shall be either a null

pointer or a unique pointer.

…

The free function causes the space pointed to by ptr to be

deallocated, that is, made available for further allocation. If ptr

is a null pointer, no action occurs. Otherwise, if the argument does

not match a pointer earlier returned by the calloc, malloc, or

realloc function, or if the space has been deallocated by a call to

free or realloc , the behavior is undefined.

So free(malloc(0)) has well defined behaviour, regardless of what

malloc(0) returns.

Dan

—

Dan Pop

CERN, IT Division

Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland

Sun, 23 Mar 2003 03:00:00 GMT Mike Mccarty

#5 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

)Greetings.

)

)I have a program that among other things utilizes a large array of structs,

)which is frequently accessed throughout the program. However, when I try to

)free() or realloc() that array (in order to resize it), it says what I typed

)in the title…For now, I’m left with a known, substantial even though

)infrequent memory leak.

)Greetings.)I have a program that among other things utilizes a large array of structs,)which is frequently accessed throughout the program. However, when I try to)free() or realloc() that array (in order to resize it), it says what I typed)in the title…For now, I’m left with a known, substantial even though)infrequent memory leak. If you are doing exactly what you said, then it is an illegal act.

#include

#define SOME_SIZE 27 /* or something */

typedef struct {

/* stuff */

} Some_t;

Some_t MyArray[SOME_SIZE];

Some_t *MyPointer;

…

MyPointer = realloc(MyArray,NewSize);

is *illegal*.

)I’ve run the program under gdb, but found nothing of real value there,

)either before the “allocated block” nor in the structs in the array I’ve

)looked into. I’ve also searched the ‘net for some info, but all I could find

)was some pretty vague reference to “char subscripting” whatever that means.

)I’ve also looked at the calloc(), memset() and malloc() calls that are used

)with this array and some of the structs in it. Still no luck. The structs in

)the array contain pointers (to strings, functions and other structs) as

)well…

)How can I find the source of this anomaly? What’s the best method here?

Well, first make sure that whatever you pass to realloc() and free()

came from malloc() or calloc(), and not somewhere else.

If this is the case, then it appears that you are accessing your array

with a negative subscript, or otherwise using invalid addresses in your

program.

)Since the program is over 100 kloc and this array used throughout it, I’m

)afraid I can’t show any really good example here.

)

)TIA,

) Fredrik

)

)

—

char *p=”char *p=%c%s%c;main(){printf(p,34,p,34);}”;main(){printf(p,34,p,34);}

This message made from 100% recycled bits.

I can explain it for you, but I can’t understand it for you.

I don’t speak for Alcatel <- They make me say that. Sun, 23 Mar 2003 03:00:00 GMT Mike Mccarty #6 / 14 "memory clobbered before allocated block"...? "memory clobbered before allocated block"...? [snip realloc() problem] )just a thought - can it be that you are malloc()ing a zero size array somewhere? )freeing it later would cause exactly the problem you describe. This is not permitted by the Standard. If malloc() succeeds, then it must pass back a pointer (non-NULL) which can be used by free(). If it fails, it must pass back NULL. )consider ) )void foo() ){ ) char *cPtr; ) unsigned aSize=get_how_many_bytes_needed(); ) cPtr=malloc(aSize); ) free(cPtr); )} )the free() will fail (most likely crash) if get_how_many_bytes_needed() returns The Standard forbids this. -- char *p="char *p=%c%s%c;main(){printf(p,34,p,34);}";main(){printf(p,34,p,34);} This message made from 100% recycled bits. I can explain it for you, but I can't understand it for you. I don't speak for Alcatel <- They make me say that. Sun, 23 Mar 2003 03:00:00 GMT Robert Stankowi #7 / 14 "memory clobbered before allocated block"...? "memory clobbered before allocated block"...? Dan Pop schrieb: Quote: > >just a thought – can it be that you are malloc()ing a zero size array somewhere?

> >freeing it later would cause exactly the problem you describe.

> >consider

> >void foo()

> >{

> > char *cPtr;

> > unsigned aSize=get_how_many_bytes_needed();

> > cPtr=malloc(aSize);

*cPtr=some_character;

Of course, the fault in my prog was:*cPtr=some_character; Quote: > > free(cPtr);

> >}

> >the free() will fail (most likely crash) if get_how_many_bytes_needed() returns

> >0

> >HTH Robert

> It doesn’t help because it’s pure bullshit!

> If the size of the space requested is zero, the behavior is

> implementation-defined; the value returned shall be either a null

> pointer or a unique pointer.

> …

> The free function causes the space pointed to by ptr to be

> deallocated, that is, made available for further allocation. If ptr

> is a null pointer, no action occurs. Otherwise, if the argument does

> not match a pointer earlier returned by the calloc, malloc, or

> realloc function, or if the space has been deallocated by a call to

> free or realloc , the behavior is undefined.

> So free(malloc(0)) has well defined behaviour, regardless of what

> malloc(0) returns.

> Dan

> —

> Dan Pop

> CERN, IT Division

> Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland

Oops – you are right, of course, should have switched on my brain and read my own

failing code before posting.

Dan,Oops – you are right, of course, should have switched on my brain and read my ownfailing code before posting. My problem was of course caused by assigning something to the location pointed to by

the returned pointer.

Shame on me and thanks for correcting me.

Anyway, I think it is easy to stumble into that trap. Some API calls return the

amount of bufferspace they require for the structs where they fill in the requested

information, then you have to malloc that amount and to set the size member of the

first struct to sizeof(this struct) before you call the API again and alas, if the

required size returned was zero — bang, either immidiately or later, when you free()

Regards – Robert

Mon, 24 Mar 2003 03:00:00 GMT Robert Stankowi

#8 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

Frederik, “Fredrik L?nnergren” schrieb:

Quote:

> >Fredrik,

> >Fredrik, > *snip*

> >just a thought – can it be that you are malloc()ing a zero size array

> somewhere?

correction: and someting assigned to it.. Quote: > >freeing it later would cause exactly the problem you describe.

> >consider

> >void foo()

> >{

> > char *cPtr;

> > unsigned aSize=get_how_many_bytes_needed();

> > cPtr=malloc(aSize);

*cPtr=something; /*cPtr is OK, but….*/

assert(cPtr);*cPtr=something; /*cPtr is OK, but….*/ Quote: > > free(cPtr);

> >}

> >the free() will fail (most likely crash) if get_how_many_bytes_needed()

> returns

> >0

> >HTH Robert

> Hmm…it’s possible, I’m not the only one coding on that…

> But in the occasions when this happens the array is always allocated for and

> populated by about 12000 elements. Could it be that one of the structs in a

> struct in the array has been 0-malloc()ed? Is the behavior you describe

> recursive into “members” so to speak?

> TIA,

> Fredrik

above.

To your question: yes, if one of the struct has a pointer to something in it and

this pointer is malloc()ed and abused in the abovementioned way.

Regards Robert

Sorry, my posting was bu..hit as Dan Pop pointed out :(, pls see my correctionabove.To your question: yes, if one of the struct has a pointer to something in it andthis pointer is malloc()ed and abused in the abovementioned way.Regards Robert

Mon, 24 Mar 2003 03:00:00 GMT Fredrik L?nnergre

#9 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Quote:

>Well, first make sure that whatever you pass to realloc() and free()

>came from malloc() or calloc(), and not somewhere else.

>Well, first make sure that whatever you pass to realloc() and free()>came from malloc() or calloc(), and not somewhere else. >If this is the case, then it appears that you are accessing your array

>with a negative subscript, or otherwise using invalid addresses in your

>program.

Was afraid of that answer; was hoping I could weasel out of going over all

that code, somehow… Oh well, thanks for the answers, everyone.

Bneh…Was afraid of that answer; was hoping I could weasel out of going over allthat code, somehow… Oh well, thanks for the answers, everyone. /Fredrik

Mon, 24 Mar 2003 03:00:00 GMT Dan P

#10 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

Quote: >Dan Pop schrieb:

>> >just a thought – can it be that you are malloc()ing a zero size array somewhere?

>> >freeing it later would cause exactly the problem you describe.

>> >consider

>> >void foo()

>> >{

>> > char *cPtr;

>> > unsigned aSize=get_how_many_bytes_needed();

>> > cPtr=malloc(aSize);

>Of course, the fault in my prog was:

>*cPtr=some_character;

then you used 1 byte!

That’s because you lied to malloc 🙂 You said that you need 0 bytes,then you used 1 byte! Dan

—

Dan Pop

CERN, IT Division

Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland

Mon, 24 Mar 2003 03:00:00 GMT Robert Stankowi

#11 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Dan Pop schrieb:

Quote:

> >Dan Pop schrieb:

> >> >just a thought – can it be that you are malloc()ing a zero size array somewhere?

> >> >freeing it later would cause exactly the problem you describe.

> >> >consider

> >> >void foo()

> >> >{

> >> > char *cPtr;

> >> > unsigned aSize=get_how_many_bytes_needed();

> >> > cPtr=malloc(aSize);

> >Of course, the fault in my prog was:

> >*cPtr=some_character;

> That’s because you lied to malloc 🙂 You said that you need 0 bytes,

> then you used 1 byte!

> Dan

> —

> Dan Pop

> CERN, IT Division

> Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland

I was fooled by an

!”$& OS” – i am sure you know that sequence: call an API function, it returns how much

space you have to allocate and then you have to put something into the first element of

the allocated array and call the API again. Of course you are checking the pointer

returned by malloc() but (I, not you) forget to check the requested size. It is not _so_

obvious, is’nt it 🙁

I just thought, the OP might have that kind of problem

thanks again for replying

Robert

Perfectly true, DanI was fooled by an !”$& OS” – i am sure you know that sequence: call an API function, it returns how muchspace you have to allocate and then you have to put something into the first element ofthe allocated array and call the API again. Of course you are checking the pointerreturned by malloc() but (I, not you) forget to check the requested size. It is not _so_obvious, is’nt it 🙁 I just thought, the OP might have that kind of problemthanks again for replyingRobert

Mon, 24 Mar 2003 03:00:00 GMT k..

#12 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

Quote:

> freeing it later would cause exactly the problem you describe.

> just a thought – can it be that you are malloc()ing a zero size array somewhere?> freeing it later would cause exactly the problem you describe. > consider

> void foo()

> {

> char *cPtr;

> unsigned aSize=get_how_many_bytes_needed();

> cPtr=malloc(aSize);

> free(cPtr);

> }

> the free() will fail (most likely crash) if get_how_many_bytes_needed()

> returns 0

Not if it’s an ANSI C implementation of `free` it won’t. —

Chris “electric hedgehog” Dollin

C FAQs at: http://www.faqs.org/faqs/by-newsgroup/comp/comp.lang.c.html

Mon, 24 Mar 2003 03:00:00 GMT Morris M. Kees

#13 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…?

…

On Thu, 05 Oct 2000 09:28:13 +0100, Robert Stankowic… Quote:

>> > cPtr=malloc(aSize); >assert(cPtr);

In C89, cPtr is not a valid argument for assert, which takes an

int argument. (In C99, any scalar argument is okay). If you

want to use assert to check that cPtr is not a null pointer, do

that explicitly, with assert(cPtr != NULL) or assert(cPtr != 0).

There are a few things wrong with this.In C89, cPtr is not a valid argument for assert, which takes anint argument. (In C99, any scalar argument is okay). If youwant to use assert to check that cPtr is not a null pointer, dothat explicitly, with assert(cPtr != NULL) or assert(cPtr != 0). But assert is a poor choice to use for run-time error checking.

If NDEBUG is not #defined with the correct value, the check won’t

even appear in your code. And if it does, reporting the source

location of the error and then aborting the program is rather

unfriendly to the end user.

—

Lucent Technologies Software Products Group

Mon, 24 Mar 2003 03:00:00 GMT Robert Stankowi

#14 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? “Morris M. Keesan” schrieb:

Quote:

> …

> >> > cPtr=malloc(aSize);

> On Thu, 05 Oct 2000 09:28:13 +0100, Robert Stankowic> …> >> > cPtr=malloc(aSize); > >assert(cPtr);

> There are a few things wrong with this.

> In C89, cPtr is not a valid argument for assert, which takes an

> int argument. (In C99, any scalar argument is okay). If you

> want to use assert to check that cPtr is not a null pointer, do

> that explicitly, with assert(cPtr != NULL) or assert(cPtr != 0).

> But assert is a poor choice to use for run-time error checking.

> If NDEBUG is not #defined with the correct value, the check won’t

> even appear in your code. And if it does, reporting the source

> location of the error and then aborting the program is rather

> unfriendly to the end user.

> —

> Lucent Technologies Software Products Group

Robert

True, Morris, thank youRobert

Tue, 25 Mar 2003 14:20:13 GMT Page 1 of 1

[ 14 post ]

Relevant Pages 1. char *ptr=”Is memory allocated here?” 2. Error “free”-ing “malloc”-ed memory 3. Allocating a memory block that doesn’t overlap physical memory 4. “No memory” while plenty of memory 5. Free a “2D dynamically allocated array” 6. Allocating “Space” 7. “Heap block” error 8. “Heap block” error 9. “duplicate insert block” message 10. UDP Win32 Socket: “recvfrom” completely blocks 11. “duplicate insert block” message 12. Allocating memory blocks

Memory Clobbered Before Allocated Block | Pointers And Dynamic Memory – Stack Vs Heap 29979 명이 이 답변을 좋아했습니다

당신은 주제를 찾고 있습니까 “memory clobbered before allocated block – Pointers and dynamic memory – stack vs heap“? 다음 카테고리의 웹사이트 https://ppa.covadoc.vn 에서 귀하의 모든 질문에 답변해 드립니다: https://ppa.covadoc.vn/blog/. 바로 아래에서 답을 찾을 수 있습니다. 작성자 mycodeschool 이(가) 작성한 기사에는 조회수 1,229,889회 및 좋아요 22,260개 개의 좋아요가 있습니다.

memory clobbered before allocated block 주제에 대한 동영상 보기

여기에서 이 주제에 대한 비디오를 시청하십시오. 주의 깊게 살펴보고 읽고 있는 내용에 대한 피드백을 제공하세요!

d여기에서 Pointers and dynamic memory – stack vs heap – memory clobbered before allocated block 주제에 대한 세부정보를 참조하세요

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In this lesson, we describe the concept of dynamic memory allocation in c or c++ and explained how memory is managed for an application. We have explained the fundamental concept of stack and heap in memory also.

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memory clobbered before allocated block 주제에 대한 자세한 내용은 여기를 참조하세요.

Memory Clobbering Error – Stack Overflow

memory clobbered before allocated block. Can someone explain the reason why free(ptr) will throw me this error?

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Source: stackoverflow.com

Date Published: 4/18/2021

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Whaddya mean I clobbered past the mem block? – C Board

memory clobbered past end of allocated block. Heres the code at causes the mem leak: Code: [View]. printf(“table at %d

”, …

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Source: cboard.cprogramming.com

Date Published: 12/3/2022

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C Language, “memory clobbered before allocated block”…?

Greetings. I have a program that among other things utilizes a large array of structs, which is frequently accessed throughout the program.

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Source: computer-programming-forum.com

Date Published: 9/15/2022

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Misaddressing_Memory

Incrementing a pointer past the end of a block of allocated memory. This is similar to the array subscript problem. Nothing stops your code from using a …

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Source: websites.umich.edu

Date Published: 8/15/2022

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Memory clobber situations – Modula-2

It can be tricky to find a good breakpoint location forthis since this chunk of memory may be legitimately deallocated and allocated multipletimes before the …

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Source: www.modula2.org

Date Published: 11/2/2021

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pointer initialization in assignment operator – c++ – DaniWeb

Hi, While executing below code i am getting error like “memory clobbered before allocated block” …

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Source: www.daniweb.com

Date Published: 6/27/2022

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주제와 관련된 이미지 memory clobbered before allocated block

주제와 관련된 더 많은 사진을 참조하십시오 Pointers and dynamic memory – stack vs heap. 댓글에서 더 많은 관련 이미지를 보거나 필요한 경우 더 많은 관련 기사를 볼 수 있습니다.

Pointers and dynamic memory – stack vs heap

주제에 대한 기사 평가 memory clobbered before allocated block

Author: mycodeschool

Views: 조회수 1,229,889회

Likes: 좋아요 22,260개

Date Published: 2013. 2. 23.

Video Url link: https://www.youtube.com/watch?v=_8-ht2AKyH4

Memory Clobbering Error

You are incrementing ptr , therefore changing the address that it points to. You can’t do that. In your case, have a separate pointer, let’s say char * p = ptr and do your operations with p leaving ptr intact so you can free(ptr) later. EDIT Taking a second look at your code, I found that you are doing ptr++ when you shouldn’t. You are accessing the characters in the array like ptr[i] , if you mess with the ptr pointer, you are changing the base address and accessing the characters with ptr[i] can lead (and will lead) to unexpected results. If you simply remove that line ( ptr++ ) your code will magically work. If you want to explore the pointer concept and try another solution, your code could look something like this:

Whaddya mean I clobbered past the mem block?

Code: Reserving 301445280 to 301445728 Alloced table at 301445216 Adding 1, 100 to 301445280 new items at 0 Size: 0 ==733== Invalid write of size 8 ==733== at 0x4009E6: insert (table.c:107) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B108 is 0 bytes inside a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1BC: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B109 is 0 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1C7: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10A is 1 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1D2: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10B is 2 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid write of size 1 ==733== at 0x11B1D1B1: memcpy (mac_replace_strmem.c:394) ==733== by 0x4009FA: insert (table.c:108) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10C is 3 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) Adding 2, 200 to 301445384 ==733== ==733== Invalid read of size 4 ==733== at 0x400A41: insert (table.c:118) ==733== by 0x4007B0: main (public02.c:26) ==733== Address 0x11F7B10C is 3 bytes after a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) ==733== ==733== Invalid read of size 4 ==733== at 0x40124E: contains (table.c:413) ==733== by 0x400D21: delete (table.c:234) ==733== by 0x4007BE: main (public02.c:27) ==733== Address 0x11F7B108 is 0 bytes inside a block of size 1 alloc’d ==733== at 0x11B1B136: malloc (vg_replace_malloc.c:149) ==733== by 0x11B1C4C0: realloc (vg_replace_malloc.c:306) ==733== by 0x40099E: insert (table.c:91) ==733== by 0x4007B0: main (public02.c:26) Size: 1 table at 301445216 Items at 301445384

C Language, “memory clobbered before allocated block”…?

“memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Author Message Fredrik L?nnergre #1 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Greetings. Greetings. I have a program that among other things utilizes a large array of structs, which is frequently accessed throughout the program. However, when I try to free() or realloc() that array (in order to resize it), it says what I typed in the title…For now, I’m left with a known, substantial even though infrequent memory leak. I’ve run the program under gdb, but found nothing of real value there, either before the “allocated block” nor in the structs in the array I’ve looked into. I’ve also searched the ‘net for some info, but all I could find was some pretty vague reference to “char subscripting” whatever that means. I’ve also looked at the calloc(), memset() and malloc() calls that are used with this array and some of the structs in it. Still no luck. The structs in the array contain pointers (to strings, functions and other structs) as well… How can I find the source of this anomaly? What’s the best method here? Since the program is over 100 kloc and this array used throughout it, I’m afraid I can’t show any really good example here. TIA, Fredrik Sun, 23 Mar 2003 03:00:00 GMT Robert Stankowi #2 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Fredrik, “Fredrik L?nnergren” schrieb: Quote: > Greetings. > I have a program that among other things utilizes a large array of structs, > which is frequently accessed throughout the program. However, when I try to > free() or realloc() that array (in order to resize it), it says what I typed > in the title…For now, I’m left with a known, substantial even though > infrequent memory leak. > I’ve run the program under gdb, but found nothing of real value there, > either before the “allocated block” nor in the structs in the array I’ve > looked into. I’ve also searched the ‘net for some info, but all I could find > was some pretty vague reference to “char subscripting” whatever that means. > I’ve also looked at the calloc(), memset() and malloc() calls that are used > with this array and some of the structs in it. Still no luck. The structs in > the array contain pointers (to strings, functions and other structs) as > well… > How can I find the source of this anomaly? What’s the best method here? > Since the program is over 100 kloc and this array used throughout it, I’m > afraid I can’t show any really good example here. > TIA, > Fredrik freeing it later would cause exactly the problem you describe. just a thought – can it be that you are malloc()ing a zero size array somewhere?freeing it later would cause exactly the problem you describe. consider void foo() { char *cPtr; unsigned aSize=get_how_many_bytes_needed(); cPtr=malloc(aSize); free(cPtr); Quote: } the free() will fail (most likely crash) if get_how_many_bytes_needed() returns HTH Robert the free() will fail (most likely crash) if get_how_many_bytes_needed() returnsHTH Robert – Hide quoted text – – Show quoted text – Quote: } Sun, 23 Mar 2003 03:00:00 GMT Fredrik L?nnergre #3 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Quote: >Fredrik, >Fredrik, *snip* >just a thought – can it be that you are malloc()ing a zero size array somewhere? >freeing it later would cause exactly the problem you describe. >consider >void foo() >{ > char *cPtr; > unsigned aSize=get_how_many_bytes_needed(); > cPtr=malloc(aSize); > free(cPtr); >} >the free() will fail (most likely crash) if get_how_many_bytes_needed() returns >0 >HTH Robert But in the occasions when this happens the array is always allocated for and populated by about 12000 elements. Could it be that one of the structs in a struct in the array has been 0-malloc()ed? Is the behavior you describe recursive into “members” so to speak? Hmm…it’s possible, I’m not the only one coding on that…But in the occasions when this happens the array is always allocated for andpopulated by about 12000 elements. Could it be that one of the structs in astruct in the array has been 0-malloc()ed? Is the behavior you describerecursive into “members” so to speak? TIA, Fredrik Sun, 23 Mar 2003 03:00:00 GMT Dan P #4 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Quote: >freeing it later would cause exactly the problem you describe. >just a thought – can it be that you are malloc()ing a zero size array somewhere?>freeing it later would cause exactly the problem you describe. >consider >void foo() >{ > char *cPtr; > unsigned aSize=get_how_many_bytes_needed(); > cPtr=malloc(aSize); > free(cPtr); >} >the free() will fail (most likely crash) if get_how_many_bytes_needed() returns >0 >HTH Robert It doesn’t help because it’s pure bullshit! If the size of the space requested is zero, the behavior is implementation-defined; the value returned shall be either a null pointer or a unique pointer. … The free function causes the space pointed to by ptr to be deallocated, that is, made available for further allocation. If ptr is a null pointer, no action occurs. Otherwise, if the argument does not match a pointer earlier returned by the calloc, malloc, or realloc function, or if the space has been deallocated by a call to free or realloc , the behavior is undefined. So free(malloc(0)) has well defined behaviour, regardless of what malloc(0) returns. Dan — Dan Pop CERN, IT Division Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland Sun, 23 Mar 2003 03:00:00 GMT Mike Mccarty #5 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? )Greetings. ) )I have a program that among other things utilizes a large array of structs, )which is frequently accessed throughout the program. However, when I try to )free() or realloc() that array (in order to resize it), it says what I typed )in the title…For now, I’m left with a known, substantial even though )infrequent memory leak. )Greetings.)I have a program that among other things utilizes a large array of structs,)which is frequently accessed throughout the program. However, when I try to)free() or realloc() that array (in order to resize it), it says what I typed)in the title…For now, I’m left with a known, substantial even though)infrequent memory leak. If you are doing exactly what you said, then it is an illegal act. #include #define SOME_SIZE 27 /* or something */ typedef struct { /* stuff */ } Some_t; Some_t MyArray[SOME_SIZE]; Some_t *MyPointer; … MyPointer = realloc(MyArray,NewSize); is *illegal*. )I’ve run the program under gdb, but found nothing of real value there, )either before the “allocated block” nor in the structs in the array I’ve )looked into. I’ve also searched the ‘net for some info, but all I could find )was some pretty vague reference to “char subscripting” whatever that means. )I’ve also looked at the calloc(), memset() and malloc() calls that are used )with this array and some of the structs in it. Still no luck. The structs in )the array contain pointers (to strings, functions and other structs) as )well… )How can I find the source of this anomaly? What’s the best method here? Well, first make sure that whatever you pass to realloc() and free() came from malloc() or calloc(), and not somewhere else. If this is the case, then it appears that you are accessing your array with a negative subscript, or otherwise using invalid addresses in your program. )Since the program is over 100 kloc and this array used throughout it, I’m )afraid I can’t show any really good example here. ) )TIA, ) Fredrik ) ) — char *p=”char *p=%c%s%c;main(){printf(p,34,p,34);}”;main(){printf(p,34,p,34);} This message made from 100% recycled bits. I can explain it for you, but I can’t understand it for you. I don’t speak for Alcatel >just a thought – can it be that you are malloc()ing a zero size array somewhere? > >freeing it later would cause exactly the problem you describe. > >consider > >void foo() > >{ > > char *cPtr; > > unsigned aSize=get_how_many_bytes_needed(); > > cPtr=malloc(aSize); *cPtr=some_character; Of course, the fault in my prog was:*cPtr=some_character; Quote: > > free(cPtr); > >} > >the free() will fail (most likely crash) if get_how_many_bytes_needed() returns > >0 > >HTH Robert > It doesn’t help because it’s pure bullshit! > If the size of the space requested is zero, the behavior is > implementation-defined; the value returned shall be either a null > pointer or a unique pointer. > … > The free function causes the space pointed to by ptr to be > deallocated, that is, made available for further allocation. If ptr > is a null pointer, no action occurs. Otherwise, if the argument does > not match a pointer earlier returned by the calloc, malloc, or > realloc function, or if the space has been deallocated by a call to > free or realloc , the behavior is undefined. > So free(malloc(0)) has well defined behaviour, regardless of what > malloc(0) returns. > Dan > — > Dan Pop > CERN, IT Division > Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland Oops – you are right, of course, should have switched on my brain and read my own failing code before posting. Dan,Oops – you are right, of course, should have switched on my brain and read my ownfailing code before posting. My problem was of course caused by assigning something to the location pointed to by the returned pointer. Shame on me and thanks for correcting me. Anyway, I think it is easy to stumble into that trap. Some API calls return the amount of bufferspace they require for the structs where they fill in the requested information, then you have to malloc that amount and to set the size member of the first struct to sizeof(this struct) before you call the API again and alas, if the required size returned was zero — bang, either immidiately or later, when you free() Regards – Robert Mon, 24 Mar 2003 03:00:00 GMT Robert Stankowi #8 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Frederik, “Fredrik L?nnergren” schrieb: Quote: > >Fredrik, > >Fredrik, > *snip* > >just a thought – can it be that you are malloc()ing a zero size array > somewhere? correction: and someting assigned to it.. Quote: > >freeing it later would cause exactly the problem you describe. > >consider > >void foo() > >{ > > char *cPtr; > > unsigned aSize=get_how_many_bytes_needed(); > > cPtr=malloc(aSize); *cPtr=something; /*cPtr is OK, but….*/ assert(cPtr);*cPtr=something; /*cPtr is OK, but….*/ Quote: > > free(cPtr); > >} > >the free() will fail (most likely crash) if get_how_many_bytes_needed() > returns > >0 > >HTH Robert > Hmm…it’s possible, I’m not the only one coding on that… > But in the occasions when this happens the array is always allocated for and > populated by about 12000 elements. Could it be that one of the structs in a > struct in the array has been 0-malloc()ed? Is the behavior you describe > recursive into “members” so to speak? > TIA, > Fredrik above. To your question: yes, if one of the struct has a pointer to something in it and this pointer is malloc()ed and abused in the abovementioned way. Regards Robert Sorry, my posting was bu..hit as Dan Pop pointed out :(, pls see my correctionabove.To your question: yes, if one of the struct has a pointer to something in it andthis pointer is malloc()ed and abused in the abovementioned way.Regards Robert Mon, 24 Mar 2003 03:00:00 GMT Fredrik L?nnergre #9 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Quote: >Well, first make sure that whatever you pass to realloc() and free() >came from malloc() or calloc(), and not somewhere else. >Well, first make sure that whatever you pass to realloc() and free()>came from malloc() or calloc(), and not somewhere else. >If this is the case, then it appears that you are accessing your array >with a negative subscript, or otherwise using invalid addresses in your >program. Was afraid of that answer; was hoping I could weasel out of going over all that code, somehow… Oh well, thanks for the answers, everyone. Bneh…Was afraid of that answer; was hoping I could weasel out of going over allthat code, somehow… Oh well, thanks for the answers, everyone. /Fredrik Mon, 24 Mar 2003 03:00:00 GMT Dan P #10 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Quote: >Dan Pop schrieb: >> >just a thought – can it be that you are malloc()ing a zero size array somewhere? >> >freeing it later would cause exactly the problem you describe. >> >consider >> >void foo() >> >{ >> > char *cPtr; >> > unsigned aSize=get_how_many_bytes_needed(); >> > cPtr=malloc(aSize); >Of course, the fault in my prog was: >*cPtr=some_character; then you used 1 byte! That’s because you lied to malloc 🙂 You said that you need 0 bytes,then you used 1 byte! Dan — Dan Pop CERN, IT Division Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland Mon, 24 Mar 2003 03:00:00 GMT Robert Stankowi #11 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Dan Pop schrieb: Quote: > >Dan Pop schrieb: > >> >just a thought – can it be that you are malloc()ing a zero size array somewhere? > >> >freeing it later would cause exactly the problem you describe. > >> >consider > >> >void foo() > >> >{ > >> > char *cPtr; > >> > unsigned aSize=get_how_many_bytes_needed(); > >> > cPtr=malloc(aSize); > >Of course, the fault in my prog was: > >*cPtr=some_character; > That’s because you lied to malloc 🙂 You said that you need 0 bytes, > then you used 1 byte! > Dan > — > Dan Pop > CERN, IT Division > Mail: CERN – IT, Bat. 31 1-014, CH-1211 Geneve 23, Switzerland I was fooled by an !”$& OS” – i am sure you know that sequence: call an API function, it returns how much space you have to allocate and then you have to put something into the first element of the allocated array and call the API again. Of course you are checking the pointer returned by malloc() but (I, not you) forget to check the requested size. It is not _so_ obvious, is’nt it 🙁 I just thought, the OP might have that kind of problem thanks again for replying Robert Perfectly true, DanI was fooled by an !”$& OS” – i am sure you know that sequence: call an API function, it returns how muchspace you have to allocate and then you have to put something into the first element ofthe allocated array and call the API again. Of course you are checking the pointerreturned by malloc() but (I, not you) forget to check the requested size. It is not _so_obvious, is’nt it 🙁 I just thought, the OP might have that kind of problemthanks again for replyingRobert Mon, 24 Mar 2003 03:00:00 GMT k.. #12 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? Quote: > freeing it later would cause exactly the problem you describe. > just a thought – can it be that you are malloc()ing a zero size array somewhere?> freeing it later would cause exactly the problem you describe. > consider > void foo() > { > char *cPtr; > unsigned aSize=get_how_many_bytes_needed(); > cPtr=malloc(aSize); > free(cPtr); > } > the free() will fail (most likely crash) if get_how_many_bytes_needed() > returns 0 Not if it’s an ANSI C implementation of `free` it won’t. — Chris “electric hedgehog” Dollin C FAQs at: http://www.faqs.org/faqs/by-newsgroup/comp/comp.lang.c.html Mon, 24 Mar 2003 03:00:00 GMT Morris M. Kees #13 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? … On Thu, 05 Oct 2000 09:28:13 +0100, Robert Stankowic… Quote: >> > cPtr=malloc(aSize); >assert(cPtr); In C89, cPtr is not a valid argument for assert, which takes an int argument. (In C99, any scalar argument is okay). If you want to use assert to check that cPtr is not a null pointer, do that explicitly, with assert(cPtr != NULL) or assert(cPtr != 0). There are a few things wrong with this.In C89, cPtr is not a valid argument for assert, which takes anint argument. (In C99, any scalar argument is okay). If youwant to use assert to check that cPtr is not a null pointer, dothat explicitly, with assert(cPtr != NULL) or assert(cPtr != 0). But assert is a poor choice to use for run-time error checking. If NDEBUG is not #defined with the correct value, the check won’t even appear in your code. And if it does, reporting the source location of the error and then aborting the program is rather unfriendly to the end user. — Lucent Technologies Software Products Group Mon, 24 Mar 2003 03:00:00 GMT Robert Stankowi #14 / 14 “memory clobbered before allocated block”…? “memory clobbered before allocated block”…? “Morris M. Keesan” schrieb: Quote: > … > >> > cPtr=malloc(aSize); > On Thu, 05 Oct 2000 09:28:13 +0100, Robert Stankowic> …> >> > cPtr=malloc(aSize); > >assert(cPtr); > There are a few things wrong with this. > In C89, cPtr is not a valid argument for assert, which takes an > int argument. (In C99, any scalar argument is okay). If you > want to use assert to check that cPtr is not a null pointer, do > that explicitly, with assert(cPtr != NULL) or assert(cPtr != 0). > But assert is a poor choice to use for run-time error checking. > If NDEBUG is not #defined with the correct value, the check won’t > even appear in your code. And if it does, reporting the source > location of the error and then aborting the program is rather > unfriendly to the end user. > — > Lucent Technologies Software Products Group Robert True, Morris, thank youRobert Tue, 25 Mar 2003 14:20:13 GMT Page 1 of 1 [ 14 post ] Relevant Pages 1. char *ptr=”Is memory allocated here?” 2. Error “free”-ing “malloc”-ed memory 3. Allocating a memory block that doesn’t overlap physical memory 4. “No memory” while plenty of memory 5. Free a “2D dynamically allocated array” 6. Allocating “Space” 7. “Heap block” error 8. “Heap block” error 9. “duplicate insert block” message 10. UDP Win32 Socket: “recvfrom” completely blocks 11. “duplicate insert block” message 12. Allocating memory blocks

The Art of Debugging with GDB, DDD, and Eclipse

0 Bąi đįnh giį Google khōng xįc minh bąi đįnh giį nhưng có kiểm tra để tģm nội dung giả vą xoį nội dung đó khi tģm thấy Viết bąi đįnh giį The Art of Debugging with GDB, DDD, and Eclipse Bởi Norman Matloff, Peter Jay Salzman

Misaddressing

OK, how did my program misaddress memory? There are many wonderful ways to misaddress memory. Here are some of the most popular ones: Overflowing an array by miscalculating an array subscript. Remember that a C/C++ array of size N is subscripted from 0 to N-1; subscripting with N is an easy error to make. Using a negative subscript happens sometimes also. For reasons of efficiency, C/C++ does not check array subscript values for validity! Using an uninitialized pointer. If a pointer variable has garbage in it, and you store into memory using the pointer, then you clobbered some random place in memory. Often you will get a warning from the compiler if you use a pointer variable without initializing it, but there are plenty of loopholes. Incrementing a pointer past the end of a block of allocated memory. This is similar to the array subscript problem. Nothing stops your code from using a pointer to access memory that isn’t yours. Not allocating memory. You certainly refer to allocated memory with a pointer variable, but just declaring a pointer variable doesn’t allocate any memory (except for pointer variable itself). A common beginner’s error is to write: char * input_buffer; cin >> input_buffer; Your program compiles and may even run. But the input is being stored into memory at whatever random address happened to be lying around in the pointer variable. Chances are you will be storing the input on top of something, and eventually you will come to grief. Try this instead: char input_buffer[200]; cin >> input_buffer; Now there is a 200-byte space allocated to store the input into. The array name “input_buffer” acts like a constant pointer to that space. This would also work – the space is allocated from the free store (or “heap”) instead of the function call stack: char * input_buffer = new char[200]; … cin >> input_buffer; Not allocating enough memory. This is really easy to do with strings. Suppose you have a char array containing a string that you want to copy into an allocated block of memory. Your code should look something like: word_pointer = new char[strlen(buffer) +1]; See the +1? The strlen function counts the number of characters in the C string in the buffer, and returns the count. BUT the null byte (‘\0’) that marks the end of the string is NOT counted. So “foo” has length 3. But to store “foo” in memory takes 4 bytes! You have to add one to get enough space for the null byte. Leaving off the +1 is a very common mistake. Overflowing an input buffer. In the above example, we have left space for an input string 199 bytes in length, reserve one for the null byte terminator. But what if your demented user types in too much? You can’t stop it! This is a form of the bugs of array overflow or incrementing a pointer past the end. This is unlikely with a buffer of size 200, but a high probability with one of, say, size 20. Dereferencing a zero pointer. The pointer value of 0 is used to mean “this pointer points at nothing.” Address 0 on almost every computer is reserved for use by the hardware or OS (e.g. for interrupt handling) . So it can never be the address of anything your program could validly create or process. For this reason, a pointer value of 0 is customarily used as a code to mean it didn’t work, it isn’t valid, don’t use, etc. But nothing stops your program from trying to use it anyway! If you try to access or store using address 0, you are again trashing memory or reading garbage. Storing at address 0 is a guaranteed crash or catastrophe, because most OS’s have vital organs in the low memory addresses. Using memory that is no longer yours. If you have returned a piece of allocated memory to the system with free or delete, you are making it available for recycling. So you should NEVER refer to it again. Nothing stops you – C/C++ assumes you know what you are doing! But if you access or store at that address again, some other part of the program or the system may be using it, and you will either get garbage or trash somebody else’s data. Some programmers set the pointer variable to 0 after free or delete to make it definite that the address of the freed memory can’t be used again, and to make the attempt to do so more obvious. A related error: A function returns a pointer to a local variable. The local variable is on the stack, and its memory is available for recycling as soon as the function returns and the stack is popped. You access the pointed-to memory, but a later function call may also use the same space! Talk about confusing! How can I find misaddressing bugs?

Memory clobber situations

Memory clobber situations For applications that allocate memory for variable sized dynamicdata structures, memory clobber problems are bugs that occur. These can be extremelydifficult to diagnose since the source of the bug is most likely completely unrelatedto the instance of the program buggy behavior. First the bug must be repeatable. If this clobber is due to anuninitialized variable bug, then the following method will probably not work. Withthat said… You first need to determine what data has been clobbered. Thisis usually not overly difficult since the program is probably acting badly due tothe clobbered data item(s). Now you need to write down the memory address of the clobbereddata. The variable name is not likely to be useful since the clobbered data is likelyto be in an allocated data structure. The data window gives you the address of alldata items. You want to set a When memory is written breakpoint onthis address. The trick here is that you will need to enter the breakpoint memorylocation as a raw address, which has no type. You do not care about the type, youjust care about the size of the type. Choose one the of the basic internal data typesthe debugger supports and coerce the raw address expression to this data type. Forexample: [12345678h]:UDWORD. This has a real address of 12345678h and the data typeis 4 bytes in size which works for integers and pointers. Now that you have your memory breakpoint set, Restart your program. You are probably going to have an annoying problem here. Thememory address you are referring to probably does not yet exist because it existsin allocated memory. Allocated memory addresses are not valid until the memory isallocated from the operating system, and when your program starts no memory has yetbeen allocated. You are probably going to need a breakpoint set somewhere in yourprogram to get you beyond the point where the memory you referencing in the memorybreakpoint has been allocated by the operating system, but everything is the programstill operating correctly. It can be tricky to find a good breakpoint location forthis since this chunk of memory may be legitimately deallocated and allocated multipletimes before the erroneous situation. Once you have this breakpoint location youwill want to disable the memory breakpoint, execute your program to the stoppingbreakpoint just discussed, and then enable the memory breakpoint. The debugger shouldnot complain about a bad expression if the memory address is valid. Note: Do not insert any memory allocation calls to makegetting a valid address easier, because it will likely change the address of yourclobbered memory location and it probably took you some time to find this location. Now run your program. Every time the memory breakpoint locationis written to by any piece of code anywhere the debugger will stop your programsexecution at that instruction. It could, and very well likely be, that most of thesewrites are correct code. Check each one and if it is okay then continue running theprogram by single stepping off the memory write and then letting the program run. If the memory block with the clobbered data is allocated anddeallocated multiple times between your stopping breakpoint and the bad memory writeyou are probably going to stop inside the memory manager of runtime system. Thisis a pain and you are just going to have to analyze if everything is still runningokay. The point here is try to get the best stopping breakpoint you can before usingthe memory breakpoint to minimize the false stops.

pointer initialization in assignment operator

Problem 1: is at lines 45 and 48. You are passing pointers to objects that are on the stack but your class assumes that the objects are on the heap and treats the pointer accordingly. Calling delete on a pointer to a stack object is always going to fail. In fact you could make your class safer by not passing a pointer in the constructor at all, if it needs to use a pointer internally that is fine, pass an int by value and have the constructor allocate the memory for it internally, that is keep all the memory management hidden inside the class. If in reality the code is using something a little more complex that an int then pass a const reference, leave the calling code resonsible for its memory and you class responsible for its internal memory. If the design requires that the pointer is passed in then use a smart pointer and let the pointer handle the memory deallocation. Problem 2: You have no copy constructor. The posted code makes no use of it so it has shown up as a problem, however best practice is if you need an assignment operator then you need a copy constructor and vice versa as generally they do very similar operations.

키워드에 대한 정보 memory clobbered before allocated block

다음은 Bing에서 memory clobbered before allocated block 주제에 대한 검색 결과입니다. 필요한 경우 더 읽을 수 있습니다.

이 기사는 인터넷의 다양한 출처에서 편집되었습니다. 이 기사가 유용했기를 바랍니다. 이 기사가 유용하다고 생각되면 공유하십시오. 매우 감사합니다!

사람들이 주제에 대해 자주 검색하는 키워드 Pointers and dynamic memory – stack vs heap

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Pointers #and #dynamic #memory #- #stack #vs #heap

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주제에 대한 기사를 시청해 주셔서 감사합니다 Pointers and dynamic memory – stack vs heap | memory clobbered before allocated block, 이 기사가 유용하다고 생각되면 공유하십시오, 매우 감사합니다.

gearmand fails with “memory clobbered before allocated block” exception, if built with –enable-debug · Issue #177 · gearman/gearmand

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t-double.c (memory clobbered before allocated block)

t-double.c (memory clobbered before allocated block)

On Wed, 27 Feb 2013, Niels Möller wrote: > I think both problems have been fixed in the gmp development repo. > Maybe you can try that version (see instructions at > http://gmplib.org/devel/repo-usage.html), and check if it works better > on your machine. The daily snapshots may be easier to use: ftp://ftp.gmplib.org/pub/snapshot/ — Marc Glisse

Misaddressing

OK, how did my program misaddress memory?

There are many wonderful ways to misaddress memory. Here are some of the most popular ones:

Overflowing an array by miscalculating an array subscript.

Remember that a C/C++ array of size N is subscripted from 0 to N-1; subscripting with N is an easy error to make. Using a negative subscript happens sometimes also. For reasons of efficiency, C/C++ does not check array subscript values for validity!

Using an uninitialized pointer.

If a pointer variable has garbage in it, and you store into memory using the pointer, then you clobbered some random place in memory. Often you will get a warning from the compiler if you use a pointer variable without initializing it, but there are plenty of loopholes.

Incrementing a pointer past the end of a block of allocated memory.

This is similar to the array subscript problem. Nothing stops your code from using a pointer to access memory that isn’t yours.

Not allocating memory.

You certainly refer to allocated memory with a pointer variable, but just declaring a pointer variable doesn’t allocate any memory (except for pointer variable itself). A common beginner’s error is to write:

char * input_buffer;

cin >> input_buffer;

Your program compiles and may even run. But the input is being stored into memory at whatever random address happened to be lying around in the pointer variable. Chances are you will be storing the input on top of something, and eventually you will come to grief.

Try this instead:

char input_buffer[200];

cin >> input_buffer;

Now there is a 200-byte space allocated to store the input into. The array name “input_buffer” acts like a constant pointer to that space.

This would also work – the space is allocated from the free store (or “heap”) instead of the function call stack:

char * input_buffer = new char[200];

…

cin >> input_buffer;

Not allocating enough memory.

This is really easy to do with strings. Suppose you have a char array containing a string that you want to copy into an allocated block of memory. Your code should look something like:

word_pointer = new char[strlen(buffer) +1];

See the +1? The strlen function counts the number of characters in the C string in the buffer, and returns the count. BUT the null byte (‘\0’) that marks the end of the string is NOT counted. So “foo” has length 3. But to store “foo” in memory takes 4 bytes! You have to add one to get enough space for the null byte. Leaving off the +1 is a very common mistake.

Overflowing an input buffer.

In the above example, we have left space for an input string 199 bytes in length, reserve one for the null byte terminator. But what if your demented user types in too much? You can’t stop it! This is a form of the bugs of array overflow or incrementing a pointer past the end. This is unlikely with a buffer of size 200, but a high probability with one of, say, size 20.

Dereferencing a zero pointer.

The pointer value of 0 is used to mean “this pointer points at nothing.” Address 0 on almost every computer is reserved for use by the hardware or OS (e.g. for interrupt handling) . So it can never be the address of anything your program could validly create or process. For this reason, a pointer value of 0 is customarily used as a code to mean it didn’t work, it isn’t valid, don’t use, etc. But nothing stops your program from trying to use it anyway! If you try to access or store using address 0, you are again trashing memory or reading garbage. Storing at address 0 is a guaranteed crash or catastrophe, because most OS’s have vital organs in the low memory addresses.

Using memory that is no longer yours.

If you have returned a piece of allocated memory to the system with free or delete, you are making it available for recycling. So you should NEVER refer to it again. Nothing stops you – C/C++ assumes you know what you are doing! But if you access or store at that address again, some other part of the program or the system may be using it, and you will either get garbage or trash somebody else’s data. Some programmers set the pointer variable to 0 after free or delete to make it definite that the address of the freed memory can’t be used again, and to make the attempt to do so more obvious.

A related error: A function returns a pointer to a local variable. The local variable is on the stack, and its memory is available for recycling as soon as the function returns and the stack is popped. You access the pointed-to memory, but a later function call may also use the same space! Talk about confusing!

How can I find misaddressing bugs?

키워드에 대한 정보 memory clobbered before allocated block

다음은 Bing에서 memory clobbered before allocated block 주제에 대한 검색 결과입니다. 필요한 경우 더 읽을 수 있습니다.

이 기사는 인터넷의 다양한 출처에서 편집되었습니다. 이 기사가 유용했기를 바랍니다. 이 기사가 유용하다고 생각되면 공유하십시오. 매우 감사합니다!

사람들이 주제에 대해 자주 검색하는 키워드 Code for Game Developers – Anatomy of a Memory Allocation

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Code #for #Game #Developers #- #Anatomy #of #a #Memory #Allocation

YouTube에서 memory clobbered before allocated block 주제의 다른 동영상 보기

주제에 대한 기사를 시청해 주셔서 감사합니다 Code for Game Developers – Anatomy of a Memory Allocation | memory clobbered before allocated block, 이 기사가 유용하다고 생각되면 공유하십시오, 매우 감사합니다.