Hello!!

A Memory leak occurs when we did not manage the memory allocation in the programs, it is the type of resource leak. Memory leak reduces the performance because it reduces the memory of the system. It is common in those languages which have no automatic garbage collection(like, c). It occurs due to the dynamic memory allocation in the program which is not reachable. As we know that the system has a finite amount of the memory, if the memory leaks occurs then it causes the big problem.

Reference: https://en.wikipedia.org/wiki/Memory_leak

A lot of tools are available in the market for detecting the memory leaks and many organization is working on this issue.

Here is the code for detecting memory leaks.

CODE:-

Header file:-findLeak.h

#define   uint                  
#define   cchar                const char                     
#define   OutFile             "/home/mani/test/MemLeakInfo.txt"   // Just Suppose
#define  MAX_FILENAME_LENGTH   256
#define  calloc(objs, nSize) 	      MyCalloc (objs, nSize, __FILE__, __LINE__)
#define  malloc(nSize) 	    	         MyMalloc (nSize, __FILE__, __LINE__)
#define  free(rMem) 		          MyFree(rMem)

// This structure is keeping info about memory leak

struct InfoMem
{
      //starting address of memory where pointer points 
    void *addr; 
      //Total size of memory in bytes which By malloc 
      //allocates  memory dynamically */
	uint nSize; 
      //Source File Name which you want
      //to  find memory leak information 
	char fileName[MAX_FILENAME_LENGTH]; 
        //Line number of source File due to                                                                             
       // which User forget to deallocate   memory 
	uint lineNumber; 
};
typedef struct InfoMem infoMem;

//This is link list of InfoMem which keeps a List of memory Leak in a source file

struct LeakMem

{
	infoMem memData;     
	struct LeakMem *nxt;   // Next Memory leak Block
};
typedef struct LeakMem leakMem;

// This function is used for writing into file to see the memory leaks summary
void WriteMemLeak(void);

// These two function add information of memory leak information when user 
// calls malloc or calloc
void SubAddMemInfo(void *rMem, uint nSize,  cchar  *file, uint lno);
void SubAdd(infoMem alloc_info);

// These two function remove and deallocated  memory and remove the leak 
//  information when user calls free function
void ResetInfo(uint pos); //erase
void DeleteAll(void); //clear(void);

// This is hidden to user , This function will call when user call malloc function
void *MyMalloc(uint size, cchar *file, uint line);
// This is hidden to user , This function will call when user call calloc function
void *MyCalloc(uint elements, uint size, cchar * file, uint lno);
// This is hidden to user , This function will call when user call free function
void  MyFree(void * mem_ref);

Source File:-findLeak.c

#include	<stdio.h>
#include	<malloc.h>
#include	<string.h>
#include	"findLeak.h"

#undef		malloc
#undef		calloc
#undef 		free


static leakMem * ptr_start = NULL;
static leakMem * ptr_next =  NULL;




// -----------------------------------------------------------
// Name: MyMalloc
// Desc: This is hidden to user. when user call malloc function then 
//       this function will be called.


void *MyMalloc (uint nSize, cchar* file, uint lineNumber)
{
	void * ptr = malloc (nSize);
	if (ptr != NULL) 
	{
		SubAddMemInfo(ptr, nSize, file, lineNumber);
	}
	return ptr;
}

// -----------------------------------------------------------
// Name: MyCalloc
// Desc: This is hidden to user. when user call calloc function then 
//       this function will be called.


void * MyCalloc (uint elements, uint nSize, const char * file, uint lineNumber)
{
	uint tSize;
	void * ptr = calloc(elements , nSize);
	if(ptr != NULL)
	{
		tSize = elements * nSize;
		SubAddMemInfo (ptr, tSize, file, lineNumber);
	}
	return ptr;
}

// -----------------------------------------------------------
// Name: SubAdd
// Desc: It's actually  Adding the Info.


void SubAdd(infoMem alloc_info)
{
	leakMem * mem_leak_info = NULL;
	mem_leak_info = (leakMem *) malloc (sizeof(leakMem));
	mem_leak_info->memData.addr = alloc_info.addr;
	mem_leak_info->memData.nSize = alloc_info.nSize;
	strcpy(mem_leak_info->memData.fileName, alloc_info.fileName); 
	mem_leak_info->memData.lineNumber = alloc_info.lineNumber;
	mem_leak_info->nxt = NULL;

	if (ptr_start == NULL)	
	{
		ptr_start = mem_leak_info;
		ptr_next = ptr_start;
	}
	else {
		ptr_next->nxt = mem_leak_info;
		ptr_next = ptr_next->nxt;				
	}

}



// -----------------------------------------------------------
// Name: ResetInfo
// Desc: It erasing the memory using by List on the basis of info( pos)


void ResetInfo(uint pos)
{

	uint index = 0;
	leakMem * alloc_info, * temp;
	
	if(pos == 0)
	{
		leakMem * temp = ptr_start;
		ptr_start = ptr_start->nxt;
		free(temp);
	}
	else 
	{
		for(index = 0, alloc_info = ptr_start; index < pos; 
			alloc_info = alloc_info->nxt, ++index)
		{
			if(pos == index + 1)
			{
				temp = alloc_info->nxt;
				alloc_info->nxt =  temp->nxt;
				free(temp);
				break;
			}
		}
	}
}

// -----------------------------------------------------------
// Name: DeleteAll
// Desc: It deletes the all elements which resides on List

void DeleteAll()
{
	leakMem * temp = ptr_start;
	leakMem * alloc_info = ptr_start;

	while(alloc_info != NULL) 
	{
		alloc_info = alloc_info->nxt;
		free(temp);
		temp = alloc_info;
	}
}


// -----------------------------------------------------------
// Name: MyFree
// Desc: 


void MyFree(void * mem_ref)
{
		uint loop;
   // if the allocated memory info is part of the list, removes it
	leakMem  *leak_info = ptr_start;
	/* check if allocate memory is in our list */
	for(loop = 0; leak_info != NULL; ++loop, leak_info = leak_info->nxt)
	{
		if ( leak_info->memData.addr == mem_ref )
		{
			ResetInfo(loop);
			break;
		}
	}
	free(mem_ref);
}


// -----------------------------------------------------------
// Name: SubAddMemInfo
// Desc: it also fill the the Info


void SubAddMemInfo (void * mem_ref, uint nSize, cchar * file, uint lineNumber)
{
	infoMem AllocInfo;

	/* fill up the structure with all info */
	memset( &AllocInfo, 0, sizeof ( AllocInfo ) );
	AllocInfo.addr 	= mem_ref;
	AllocInfo.nSize = nSize;
	strncpy(AllocInfo.fileName, file, MAX_FILENAME_LENGTH);
	AllocInfo.lineNumber = lineNumber;
	
	/* SubAdd the above info to a list */
	SubAdd(AllocInfo);
}

// -----------------------------------------------------------
// Name: WriteMemLeak
// Desc: It writes information about Memory leaks in a file 
//       Example: File is as : "/home/asadulla/test/MemLeakInfo.txt"



void WriteMemLeak(void)
{
	uint index;
	leakMem *leak_info;

	FILE * fp_write = fopen(OutFile, "wt");
	char info[1024];

	if(fp_write != NULL)
	{
		sprintf(info, "%s\n", "SUMMARY ABOUT MEMORY LEAKS OF YOUR SOURCE FILE ");
		fwrite(info, (strlen(info) + 1) , 1, fp_write);
		sprintf(info, "%s\n", "-----------------------------------");	
		fwrite(info, (strlen(info) + 1) , 1, fp_write);
		
		for(leak_info = ptr_start; leak_info != NULL; leak_info = leak_info->nxt)
		{

			sprintf(info, "Name of your Source File                 : %s\n", leak_info->memData.fileName);
			fwrite(info, (strlen(info) + 1) , 1, fp_write);

			sprintf(info, "Starting Address                         : %d\n", leak_info->memData.addr);
			fwrite(info, (strlen(info) + 1) , 1, fp_write);

			sprintf(info, " Total size Of memory Leak               : %d bytes\n", leak_info->memData.nSize);			
			fwrite(info, (strlen(info) + 1) , 1, fp_write);

			sprintf(info, "Line Number for which no DeAllocation    : %d\n", leak_info->memData.lineNumber);
			fwrite(info, (strlen(info) + 1) , 1, fp_write);

			sprintf(info, "%s\n", "-----------------------------------");	
			fwrite(info, (strlen(info) + 1) , 1, fp_write);
      fwrite(info, (strlen(info) + 1) , 1, fp_write);
		}
	}	

DeleteAll();
}

The user has to include these two files in their program to find the memory leaks.

Source File : test.c -  Here is an example.

#include<malloc.h>
#include"findLeak.h"

int main()
{
	int *p1 = (int *)malloc(10);  
	int *p2 = (int *)calloc(10, sizeof(int));
    char *p3 = (char *) calloc(15, sizeof(float));
    float *p4 = (float*) malloc(16);
	free(p2);
    WriteMemLeak();
	return 0;
 }

Output of the test program is:-

SUMMARY ABOUT MEMORY LEAKS OF YOUR SOURCE FILE 
-----------------------------------
Name of your Source File                 : test.c
Starting Address                         : 184960
 Total size Of memory Leak               : 10 bytes
Line Number for which no DeAllocation    : 7
-----------------------------------
-----------------------------------
Name of your Source File                 : test.c
Starting Address                         : 187104
 Total size Of memory Leak               : 60 bytes
Line Number for which no DeAllocation    : 9
-----------------------------------
-----------------------------------
Name of your Source File                 : test.c
Starting Address                         : 184984
 Total size Of memory Leak               : 16 bytes
Line Number for which no DeAllocation    : 10
-----------------------------------
-----------------------------------