how to trace memory leaks in c++: windows source code example

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How to trace memory leaks C++ with a few lines of code:
free source code for instant use in windows projects.

starting point: let's say we have a simple C++ program like this:

#include <stdio.h>
#include <string.h>

char *joinStrings(char *p1, char *p2)
{
   int nlen1 = strlen(p1);
   int nlen2 = strlen(p2);
   char *pres = new char[nlen1+nlen2+10];
   strcpy(pres, p1);
   strcat(pres, p2);
   return pres;
}

int main(int argc, char *argv[])
{
   printf("string concatenation test:\n");
   char *psz1 = "hello";
   char *psz2 = "world";
   char *pszj = joinStrings(psz1, psz2);
   printf("result: %s\n", pszj);
   return 0;
}

this program seems to run without problems, producing this output:

   string concatenation test:
   result: helloworld

however we don't really know if all memory has been freed.

to find out, download memdeb.cpp from here and extend the example like this:

#include <stdio.h>
#include <string.h>

#include "memdeb.cpp"

char *joinStrings(char *p1, char *p2)
{
   int nlen1 = strlen(p1);
   int nlen2 = strlen(p2);
   char *pres = new char[nlen1+nlen2+10];
   strcpy(pres, p1);
   strcat(pres, p2);
   return pres;
}

int main(int argc, char *argv[])
{
   printf("string concatenation test:\n");
   char *psz1 = "hello";
   char *psz2 = "world";
   char *pszj = joinStrings(psz1, psz2);
   printf("result: %s\n", pszj);

   listMemoryLeaks();

   return 0;
}

now, the program produces this output:

string concatenation test:
result: helloworld
MEM LEAK: adr 32075ch, size 20, alloc'ed in test.cpp 10
[SMEMDEBUG: 1 new's, 0 delete's, 0 errors, 1 leaks]

if you want to integrate the memory tracing into a project with several .cpp files, include it everywhere, defining in most files

#define MEMDEB_JUST_DECLARE

before the include. only in one .cpp file, leave out this define. it should also be easy to split memdeb.cpp into a .hpp and .cpp, as the code is rather short.

NOTE:

as all free stuff, SFK memory tracing comes without any warranty
it eats some performance when used with many memory objects
it is not thread safe

and if you integrate this into a project, always do it in a way which allows (de)activation through a define, e.g.

   #ifdef WITH_MEMORY_TRACING
     #include "memdeb.cpp"
   #endif

SFK memory tracing is used to track memory leaks in the text file processor swiss file knife. read more about sfk here.

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