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In this example, a file is opened for reading. If the file is opened successfully, memory is allocated by malloc() and referenced by str. A message indicating that the file was opened properly is copied into the dynamically-allocated memory referenced by str and printed. Afterwards, the memory is deallocted by calling free()}. If the file does not open correctly, however, {{str is set to a string literal. Because str now references memory that was not dynamically allocated, an error will occur when this memory is freed.

Code Block

  FILE *file = NULL;
  char *str  = NULL, *fname="~/config_file";
  size_t size = 100;

  file = fopen("~/config_file","r");
  if (file != NULL) {
    str = (char *)malloc(size);
  if (str == NULL) {  
    /* Handle Allocation Error */
  }
  snprintf(str, size, "File %s opened properly", fname);
    printf("LOG: %s\n", str);
  }
  else {
    str = "ERROR OPENING FILE";
    printf("LOG: %s\n", str);
  }
  free(str);

Compliant Solution 1

In the compliant solution, the call to free() has been moved inside the conditional statement to ensure that only dynamic memory is freed.

Code Block

  FILE *file = NULL;
  char *str  = NULL, *fname="~/config_file";
  size_t size = 100;

  file = fopen("~/config_file","r");
  if (file != NULL) {
    str = (char *)malloc(size);
   if (str == NULL) {  
     /* Handle Allocation Error */
   }
   snprintf(str, size, "File %s opened properly", fname);
    printf("LOG: %s\n", str);
    free(str);   /* only dynamic memory is freed */
  }
  else {
    str = "ERROR OPENING FILE";
    printf("LOG: %s\n", str);
  }

Non-compliant Code Example 2

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Compliant Solution 1

Non-compliant Code Example 2