Synopsis

A variable assigned using a library function that can return -1 as an error value is subsequently used where the value must be non-negative.

Enabled by default

Yes

Severity/Certainty

Medium/Medium

Full description

A variable assigned using a library function which can return -1 as an error value is subsequently used as a subscript or a size, both of which require the value to be non-negative. This might cause a crash or unpredictable behavior. These functions are inspected: ftell(), clock(), time(), mktime(), fprintf(), printf(), sprintf(), vfprintf(), vprintf(), vsprintf(), mblen(), mbstowcs(), mbstowc(), wcstombs(), and wctomb().

Coding standards

Code examples

The following code example fails the check and will give a warning:

#include <time.h>
#include <stdlib.h>

void example(void) {
  time_t time = clock();
  int *block = malloc(time); // time is used in a
                 // situation requiring it to be non-
                 // negative, but clock() may return -1
}

The following code example passes the check and will not give a warning about this issue:

#include <time.h>
#include <stdlib.h>

void example(void) {
  time_t time = clock();
  if (time>0){
    int *block = malloc(time); // OK - time is checked
  }
}