Thread: How to correct the problem?

  1. #1
    Registered User
    Join Date
    Jan 2008
    Posts
    7

    Angry How to correct the problem?

    In Linux, I have following instructions from main() function:
    Code:
    #include <stdio.h>
    char* testFn1(const char* sampleString)
    {
    
    }
    
    int main()
    {
                 char *inputString, *outString;
                 inputString = malloc(13*sizeof(char));   //line number 41
                inputString = "Sample Input";
                  outString = testFn1(inputString);
                free(inputString);
    }
    When I run this program in valgrind to check the memory leaks, it reports as follows:
    ==22554== 1 errors in context 1 of 1:
    ==22554== Invalid free() / delete / delete[]
    ==22554== at 0x4004EFA: free (vg_replace_malloc.c:235)
    ==22554== by 0x80486C5: main (ex54.c:50)
    ==22554== Address 0x80488CD is not stack'd, malloc'd or (recently) free'd
    --22554--
    --22554-- supp: 12 Ubuntu-stripped-ld.so
    ==22554==
    ==22554== IN SUMMARY: 1 errors from 1 contexts (suppressed: 12 from 1)
    ==22554==
    ==22554== malloc/free: in use at exit: 13 bytes in 1 blocks.
    ==22554== malloc/free: 3 allocs, 3 frees, 32 bytes allocated.
    ==22554==
    ==22554== searching for pointers to 1 not-freed blocks.
    ==22554== checked 47,188 bytes.
    ==22554==
    ==22554==
    ==22554== 13 bytes in 1 blocks are definitely lost in loss record 1 of 1
    ==22554== at 0x4004405: malloc (vg_replace_malloc.c:149)
    ==22554== by 0x8048660: main (ex54.c:41)
    ==22554==
    ==22554== LEAK SUMMARY:
    ==22554== definitely lost: 13 bytes in 1 blocks.
    ==22554== possibly lost: 0 bytes in 0 blocks.
    ==22554== still reachable: 0 bytes in 0 blocks.
    ==22554== suppressed: 0 bytes in 0 blocks.
    --22554-- memcheck: sanity checks: 0 cheap, 1 expensive

    I don't understand why the malloc and free of inputString are reported as problematic. What is wrong in those statements. How to correct them?

  2. #2
    Hurry Slowly vart's Avatar
    Join Date
    Oct 2006
    Location
    Rishon LeZion, Israel
    Posts
    6,794
    to copy strings in c you need to use strcpy function

    in your case - you loose the pointer to malloced memory - storing in the var address of the const string...
    All problems in computer science can be solved by another level of indirection,
    except for the problem of too many layers of indirection.
    David J. Wheeler

  3. #3
    Registered User
    Join Date
    Jan 2008
    Posts
    7

    Problem solved

    Thanks Vart,

    After using strcpy, that memory leak is not happening.

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