Synopsis

A pointer is dereferenced, then compared with NULL.

Enabled by default

Yes

Severity/Certainty

High/Medium

Full description

A pointer is dereferenced, then compared with NULL. Dereferencing a pointer implicitly asserts that it is not NULL. Comparing it with NULL after this suggests that it might have been NULL when it was dereferenced. This check is identical to CERT-EXP34-C_e.

Coding standards

Code examples

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

#include <stdlib.h>

int example(void) {
  int *p;
  *p = 4;  //line 8 asserts that p may be NULL  
  if (p != NULL) {
    return 0;
  }
  return 1;
}

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

#include <stdlib.h>

void example(int *p) {
  if (p == NULL) {
    return;
  }
  *p = 4;
}