Program crashes only in Release mode outside debugger

Asked 2010-02-27T13:59:10.493

I have quite massive program (>10k lines of C++ code). It works perfectly in debug mode or in release mode when launched from within Visual Studio, but the release mode binary usually crashes when launched manually from the command line (not always!!!).

The line with delete causes the crash:

bool Save(const short* data, unsigned int width, unsigned int height, 
          const wstring* implicit_path, const wstring* name = NULL, 
          bool enable_overlay = false)
{
    char* buf = new char[17];
    delete [] buf;
}

EDIT: Upon request expanded the example.

The "len" has length 16 in my test case. It doesn't matter, if I do something with the buf or not, it crashes on the delete.

EDIT: The application works fine without the delete [] line, but I suppose it leaks memory then (since the block is never unallocated). The buf in never used after the delete line. It also seems it does not crash with any other type than char. Now I am really confused.

The crash message is very unspecific (typical Windows "xyz.exe has stopped working"). When I click the "Debug the program" option, it enters VS, where the error is specified to be "Access violation writing location xxxxxxxx". It is unable to locate the place of the error though "No symbols were loaded for any stack frame".

I guess it is some pretty serious case of heap corruption, but how to debug this? What should I look for?

Thanks for help.

Edit Report

3 Answers

You probably have a memory overwrite somewhere and the delete[] is simply the first time it causes a problem. But the overwrite itself can be located in a totally different part of your program. The difficulty is finding the overwrite.

Add the following function

#include <malloc.h>

#define CHKHEAP()  (check_heap(__FILE__, __LINE__))

void check_heap(char *file, int line)
{
    static char *lastOkFile = "here";
    static int lastOkLine = 0;
    static int heapOK = 1;

    if (!heapOK) return;

    if (_heapchk() == _HEAPOK)
    {
        lastOkFile = file;
        lastOkLine = line;
       return;
    }

    heapOK = 0;
    printf("Heap corruption detected at %s (%d)\n", file, line);
    printf("Last OK at %s (%d)\n", lastOkFile, lastOkLine);
}

Now call CHKHEAP() frequently throughout your program and run again. It should show you the source file and line where the heap becomes corrupted and where it was OK for the last time.

answered 2010-02-27T14:36:13.133

Have you tried simply isolating this with the same build file but code based just on what you've put above? Something like:

int main(int argc, char* argv[] )
{
    const int len( 16 );
    char* buf = new char[len + 1]; 

    delete [] buf;
}

The code you've given is absolutely fine and, on it's own, should run with no problems either in debug or optimised. So if the problem isn't down to specifics of your code, then it must be down to specifics of the project (i.e. compilation / linkage)

Have you tried creating a brand new project and placing the 10K+ lines of C++ into it? Might not take too long to prove the point. Especially if the existing project has either been imported in or heavily altered.

answered 2010-02-27T14:33:12.767

I was having the same issue, and I figured out that my program was only crashing when I went to delete[] char pointers with a string length of 1.

void DeleteCharArray(char* array){
 if(strlen(array)>1){delete [] array;}
 else{delete array;}
}

This fixed the issue, but it is still error prone, but could be modified to be otherwise. Anyhow the reason this happens I suspect is that to C++ char* str=new char[1] and char* str=new char; are the same thing, and that means that when you're trying to delete a pointer with delete[] which is made for arrays only then results are unexpected, and often fatal.

answered 2011-09-17T21:17:18.630

Program crashes only in Release mode outside debugger

3 Answers

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