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I'm aware that asprintf() allocates memory and this needs to be freed after it's called. I added free statements for the pointers provided to asprintf (after they're used), yet valgrind reports that I still have memory leaks:

==2697== HEAP SUMMARY:
==2697==     in use at exit: 0 bytes in 12 blocks
==2697==   total heap usage: 401 allocs, 389 frees, 15,015 bytes allocated
==2697== 
==2697== 0 bytes in 6 blocks are definitely lost in loss record 1 of 2
==2697==    at 0x4C2DB2F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2697==    by 0x1094BB: experiment (hw2pt2.c:235)
==2697==    by 0x4E416C9: start_thread (pthread_create.c:333)
==2697== 
==2697== 0 bytes in 6 blocks are definitely lost in loss record 2 of 2
==2697==    at 0x4C2DB2F: malloc (in /usr/lib/valgrind/vgpreload_memcheck-amd64-linux.so)
==2697==    by 0x1094CC: experiment (hw2pt2.c:236)
==2697==    by 0x4E416C9: start_thread (pthread_create.c:333)
==2697== 
==2697== LEAK SUMMARY:
==2697==    definitely lost: 0 bytes in 12 blocks
==2697==    indirectly lost: 0 bytes in 0 blocks
==2697==      possibly lost: 0 bytes in 0 blocks
==2697==    still reachable: 0 bytes in 0 blocks
==2697==         suppressed: 0 bytes in 0 blocks

...so now all the bytes are freed but I still have allocated blocks? How do I fix this. Also here's the section of code where this is going on (including hw2pt2.c:235 & 236, which are the asprintf lines).

char *results = (char *)malloc(0);
  for (int i = 0; i < NUM_THREADS; i++) {
    char *str1 = (char *)malloc(0);
    char *str2 = (char *)malloc(0);
    asprintf(&str1, "\tProducer Thread %d slept %d times\n", i, r_vals[i]);
    asprintf(&str2, "\tConsumer Thread %d slept %d times\n", i, r_vals[i+2]);
    int len = strlen(str1)+strlen(str2)+strlen(results);
    results = (char *)realloc(results, len*sizeof(char));
    strcat(results, str1);
    strcat(results, str2);
    free(str1);
    free(str2);
  }

PS - "*results" is freed later in the program

Austin Rosenberg
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  • Off by 1. `results = (char *)realloc(results, len*sizeof(char));` --> `results = realloc(results, len+1u);` Code did not account for the _null character_, so the later `strcat()` over-wrote memory. – chux - Reinstate Monica Oct 11 '17 at 18:05
  • asprintf allocate the string, it will ignore and erase value in str1 and str2 – Stargateur Oct 11 '17 at 18:08
  • First call to `strlen(results)` is a problem too. `results` does not point to a _string_. – chux - Reinstate Monica Oct 11 '17 at 18:09
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    Do not `malloc(0)` to initialize `str1` and `str2`. You need not initialize them at all because `asprintf()` will assign values to them on success, but if you do initialize them then initialize them to `NULL`. Very likely those `malloc()`s are responsible for the zero-byte blocks. – John Bollinger Oct 11 '17 at 18:09
  • Note: `asprintf()` returns the number of bytes printed (or -1). Code could use `len1 = int asprintf(&str1, ...); ... int len = len1 + ...` rather than calling `strlen(str1)` unnecessarily. – chux - Reinstate Monica Oct 11 '17 at 18:19

0 Answers0