memory leaking from stdin in C

Question

I have got into a problem of memory leak in my code. I believe it is from stdin . I tried to close(0), did not work. Below is my code

 char line[MAX_BUFFER] = {};
    char *commands;
    while(!feof(stdin)) {
         fputs("? ",stdout);

        if(fgets(line, MAX_BUFFER , stdin))
        {
            Command cmd = {};
            commands =  parse(&cmd, line);
            printf("%s",commands);
           free(commands);

         }

    }

    return 0;

my parse.c basically do this

    char result[250] = "some text string here";
    char *target  = malloc(sizeof(char) * 250);
    target = strdup(result);
    return target

and my valgrind output looks like this

==26303== FILE DESCRIPTORS: 3 open at exit.
==26303== Open file descriptor 2: /dev/pts/4
==26303==    <inherited from parent>
==26303== 
==26303== Open file descriptor 1: /dev/pts/4
==26303==    <inherited from parent>
==26303== 
==26303== Open file descriptor 0: /dev/pts/4
==26303==    <inherited from parent>
==26303== 
==26303== 
==26303== HEAP SUMMARY:  
==26303==     in use at exit: 500 bytes in 2 blocks
==26303==   total heap usage: 4 allocs, 2 frees, 545 bytes allocated
==26303== 
==26303== 500 bytes in 2 blocks are definitely lost in loss record 1 of 1

The `parse` source code is *necessary* to post to analyze this. Also see [Why is “while ( !feof (file) )” always wrong?](https://stackoverflow.com/questions/5431941/why-is-while-feof-file-always-wrong) — Eugene Sh., May 25 '18 at 14:28
What pointer are you returning in your parse method (what is return *) ? Can you post the method signature of parse also. — auburg, May 25 '18 at 14:39
`malloc()` followed by `strdup()` allocates two lots of memory. Then only one of them is released in the calling code. So it's your allocations of memory that present the memory leak, not usage of `stdin`. — Peter, May 25 '18 at 14:40
You allocated the memory twice . Strdup() does mem allocation and copy. You don’t have to do malloc if you use strdup() to copy the string. — danglingpointer, May 25 '18 at 14:41

score 0 · Accepted Answer · answered May 25 '18 at 18:12

Both strdup() and malloc() are allocating memory! You can get rid of the second line in your parse.c and edit the third to say

char * target = strdup(result);

and it would work fine.

Also don't forget to free the memory once you're done with it using free(pointerToMemoryAllocated)

memory leaking from stdin in C

1 Answers1