Synopsis

Do not compare padding data.

Enabled by default

Yes

Severity/Certainty

Medium/High

Full description

Padding values are unspecified, attempting a byte-by-byte comparison between structures can lead to incorrect results.

Coding standards

Code examples

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

#include <string.h>

struct s {
  char c;
  int i;
  char buffer[13];
};

void compare(const struct s *left, const struct s *right) { 
  if ((left && right) &&
      (0 == memcmp(left, right, sizeof(struct s)))) {
    /* ... */
  }
}

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

#include <string.h>

struct s {
  char c;
  int i;
  char buffer[13];
};

void compare(const struct s *left, const struct s *right) { 
  if ((left && right) &&
      (left->c == right->c) &&
      (left->i == right->i) &&
      (0 == memcmp(left->buffer, right->buffer, 13))) {
    /* ... */
  }
}