Visual Studio 6 (sp6) producing memory leaks?
Author
Greetings!
I was playing arround with memory leak detection in Visual C++ 6. Micro$oft has build in a memory leak detector which can be included as:
#include <crtdbg.h>
int main(void)
{
_CrtDumpMemoryLeaks();
return 0;
}
It only works in debug mode. When running that program in visual C++ 7 or 7.1 it works fine, but in Visual C++ 6 it throws me memory leak report?! Why?! The program is empty!!! Another demo:
int main(void)
{
//sorry error:int new;
new int;
_CrtDumpMemoryLeaks();
return 0;
}
In Visual C++ 7/7.1 it produces 4 byte memory leak (one int) but in visual C 6 (on all available service packs) it throws a report. What is going on? Does anoyne have a clue?
[Edited by - Samurai Jack on May 25, 2005 4:56:20 AM]
I think you are mistaken somewhere. The first example gives no memory leaks at all in MSVC 6.0. The second example will not compile because 'new' is a reserved keyword. If declared with a different name it does not give a memory leak (correctly) because the memory is allocated statically and released immediately when main() ends.
Greetz,
Illco
Greetz,
Illco
Author
I get memory leaks all the time in Visual C++ 6 Enterprise with SP6 with souch simple programs. Maybe someone else could try too?
It works fine in VS 7 or VS 7.1 (all licensed and updated).
There was an error:
int new;
should be:
new int; //memory leak
You should run the samples with (Start Debug->GO)=F5 not CTRL+F5!
It works fine in VS 7 or VS 7.1 (all licensed and updated).
There was an error:
int new;
should be:
new int; //memory leak
You should run the samples with (Start Debug->GO)=F5 not CTRL+F5!
Quote:
should be:
new int; //memory leak
With this it reports the memory leak in MSVC 6.0 like it should.
Quote:
You should run the samples with (Start Debug->GO)=F5 not CTRL+F5!
Trust me, I know. Yes, maybe someone else can try.
Ilco is quite right. I tried, too. And, as he says, the MSVC leak detector works as it should.
Author
This was just a demonstration to produce a 4 byte memory leak.
So "new int;" should produce 4 byte memory leak which was supposed to be reported.
I get a report like this:
The first block is 4 bytes long, which is ok, because i forced it to be there. But what about the 33 bytes long chunk, which appears in both applications?
The version I'm using is: Visual Studio 6 Enterprise Edition (SP6).
So "new int;" should produce 4 byte memory leak which was supposed to be reported.
I get a report like this:
int main() { _CrtDumpMemoryLeaks(); return 0; } :Quote:
Loaded 'ntdll.dll', no matching symbolic information found.
Loaded 'C:\WINDOWS\system32\kernel32.dll', no matching symbolic information found.
Detected memory leaks!
Dumping objects ->
{41} normal block at 0x003208E8, 33 bytes long.
Data: < C > 00 43 00 CD CD CD CD CD CD CD CD CD CD CD CD CD
{40} normal block at 0x00320880, 40 bytes long.
Data: < C > EC 11 43 00 16 00 00 00 00 00 00 00 00 00 00 00
Object dump complete.
The thread 0x2DC has exited with code 0 (0x0).
The program 'c:\brisito7\Debug\brisito7.exe' has exited with code 0 (0x0).
int main() { new int; _CrtDumpMemoryLeaks(); return 0; } :Quote:
Loaded 'ntdll.dll', no matching symbolic information found.
Loaded 'C:\WINDOWS\system32\kernel32.dll', no matching symbolic information found.
Detected memory leaks!
Dumping objects ->
{42} normal block at 0x00320950, 4 bytes long.
Data: < > CD CD CD CD
{41} normal block at 0x003208E8, 33 bytes long.
Data: < C > 00 43 00 CD CD CD CD CD CD CD CD CD CD CD CD CD
{40} normal block at 0x00320880, 40 bytes long.
Data: < C > EC 11 43 00 16 00 00 00 00 00 00 00 00 00 00 00
Object dump complete.
The thread 0x48C has exited with code 0 (0x0).
The program 'c:\brisito7\Debug\brisito7.exe' has exited with code 0 (0x0).
The first block is 4 bytes long, which is ok, because i forced it to be there. But what about the 33 bytes long chunk, which appears in both applications?
The version I'm using is: Visual Studio 6 Enterprise Edition (SP6).
Quote:Original post by Samurai Jack
This was just a demonstration to produce a 4 byte memory leak.
So "new int;" should produce 4 byte memory leak which was supposed to be reported.
I get a report like this:int main() { _CrtDumpMemoryLeaks(); return 0; } :Quote:
Loaded 'ntdll.dll', no matching symbolic information found.
Loaded 'C:\WINDOWS\system32\kernel32.dll', no matching symbolic information found.
Detected memory leaks!
Dumping objects ->
{41} normal block at 0x003208E8, 33 bytes long.
Data: < C > 00 43 00 CD CD CD CD CD CD CD CD CD CD CD CD CD
{40} normal block at 0x00320880, 40 bytes long.
Data: < C > EC 11 43 00 16 00 00 00 00 00 00 00 00 00 00 00
Object dump complete.
The thread 0x2DC has exited with code 0 (0x0).
The program 'c:\brisito7\Debug\brisito7.exe' has exited with code 0 (0x0).int main() { new int; _CrtDumpMemoryLeaks(); return 0; } :Quote:
Loaded 'ntdll.dll', no matching symbolic information found.
Loaded 'C:\WINDOWS\system32\kernel32.dll', no matching symbolic information found.
Detected memory leaks!
Dumping objects ->
{42} normal block at 0x00320950, 4 bytes long.
Data: < > CD CD CD CD
{41} normal block at 0x003208E8, 33 bytes long.
Data: < C > 00 43 00 CD CD CD CD CD CD CD CD CD CD CD CD CD
{40} normal block at 0x00320880, 40 bytes long.
Data: < C > EC 11 43 00 16 00 00 00 00 00 00 00 00 00 00 00
Object dump complete.
The thread 0x48C has exited with code 0 (0x0).
The program 'c:\brisito7\Debug\brisito7.exe' has exited with code 0 (0x0).
The first block is 4 bytes long, which is ok, because i forced it to be there. But what about the 33 bytes long chunk, which appears in both applications?
The version I'm using is: Visual Studio 6 Enterprise Edition (SP6).
Its probably just global memory that you're not responsible for. Calling _CrtDumpMemoryLeaks() at the end of main() only gets you so far. As I recall [its been a while since I used this], the following code is a better solution:
int main(){_CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG) | _CRTDBG_LEAK_CHECK_DF);new int;}That'll cause the report to be after all the global memory has been released, so all you've got left is actual leaks.
*edit:
Got my test running right...it seems to work as intended. Note, I never see the stuff you report, possibly due to my use of a later version of the compiler/libraries.
class NoLeak{public: NoLeak() {p = new int;} ~NoLeak() {delete p;} int* p;};int main(){ NoLeak this_wont_leak; int* this_will_leak = new int; _CrtSetDbgFlag(_CrtSetDbgFlag(_CRTDBG_REPORT_FLAG) | _CRTDBG_LEAK_CHECK_DF); _CrtDumpMemoryLeaks();}Result:
Detected memory leaks!Dumping objects ->{46} normal block at 0x00322D60, 4 bytes long. Data: < > CD CD CD CD {45} normal block at 0x00322D20, 4 bytes long. Data: < > CD CD CD CD Object dump complete.Detected memory leaks!Dumping objects ->{46} normal block at 0x00322D60, 4 bytes long. Data: < > CD CD CD CD Object dump complete.CM
Using a memory leak detector tool, something happened to me once. I opened an application which I knew didn't leak. And there was always a couple of bytes leak reported. I wsa wondering what it is, since there was no usable information. Then , I retried the same test later, and the leak was gone. So, it may just mean that sometimes, something that is external to your application might interfere with the detection.
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