Use size_t for all integer values representing the size of an object

The size_t type is the unsigned integer type of the result of the sizeof operator. The underlying representation of variables of type size_t are guaranteed to be of sufficient precision to represent the size of an object. The limit of size_t is specified by the SIZE_MAXmacro. 

Any variable which is used to represent the size of an object including, but not limited to, integer values used as sizes, indices, loop counters, and lengths should be declared as size_t.

Non-compliant Code Example 1

In the following example, the dynamically allocated buffer referenced by p will overflow for values of n > INT_MAX.

char *copy(size_t n, char *str) {
  int i;
  char *p = malloc(n);
  for ( i = 0; i < n; ++i ) {
    p[i] = *str++;
  }
  return p;
}

char *p = copy(20, "hi there");

Compliant Code Example 1

Declaring i to be of type size_teliminates the possible integer overflow condition.

char *copy(size_t n, char *str) {
  size_t i;
  char *p = malloc(n);
  for ( i = 0; i < n; ++i ) {
    p[i] = *str++;
  }
  return p;
}

char *p = copy(20, "hi there");

References

• ISO/IEC 9899:1999 Section 7.17 Common definitions <stddef.h>