(C) Memory leak

When a program dynamically creates new ?instances by malloc without ?freeing it in the end.

A common beginner's error is forgetting to call ?free

{
  char * myString = malloc(sizeof(char)*10); //Allocate memory for 10 chars
  //Forget to write 'free (myString)'
}

Generate a memory leak

To see what ?errors might occur.

include <stdlib.h>

int main()
{
  while(1)
  {
    int * i = malloc(10000000);
  }
}

Note: I did not get noticed of an ?error under C++ Builder 6.0. The program just leaked in silence.

Visual Studio

To prevent memory leaks in Visual Studio, when working in console application, add the lines below to your code.

include <crtdbg.h>


int main()
{
  void* leak = malloc(1234);
  _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
  return 0;
}

To find out the allocation that causes the leak, elaborate with:

int __cdecl MyAllocHook(
  int      nAllocType,
  void   * pvData,
  size_t   nSize,
  int      nBlockUse,
  long     lRequest,
  const unsigned char * szFileName,
  int      nLine
  )
{
  //Set a conditional breakpoint to break on the leaking 'lRequest'
  return true; // Allow the memory operation to proceed
}
void* leak()
{
	return malloc(1234);
}
int main()
{
  _CrtSetDbgFlag(_CRTDBG_ALLOC_MEM_DF | _CRTDBG_LEAK_CHECK_DF);
  _CrtSetAllocHook( MyAllocHook );
  leak();
}

'Memory leak' links

last edited (February 7, 2007) by bilderbikkel, Number of views: 1702, Current Rev: 4 (Diff)

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