Synopsis

Do not dereference null pointers.

Enabled by default

Yes

Severity/Certainty

High/High

Full description

Dereferencing a null pointer is undefined behavior. On many platforms, dereferencing a null pointer results in abnormal program termination, but this is not required by the standard.

Coding standards

Code examples

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

#include <stdlib.h>
#include <string.h>

void * maybe_return_null(int num, void *p) {
  if (num % 2) {
    return NULL;
  }
  return p;
}

void example(void *usr_data, int length) {
  int *ptr = malloc(sizeof(int));
  ptr = maybe_return_null(length, ptr);
  memcpy(ptr, usr_data, length);
}

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

#include <stdlib.h>
#include <string.h>

void * maybe_return_null(int num, void *p) {
  if (num % 2) {
    return NULL;
  }
  return p;
}

void example(void *usr_data, int length) {
  int *ptr = malloc(sizeof(int));
  ptr = maybe_return_null(length, ptr);
  if (ptr != NULL) {
    memcpy(ptr, usr_data, length);
  }
}