The type {{size_t}} generally covers the entire address space.  \[[TR 24731-1|AA. C References#ISO/IEC TR 24731-1-2007]\] introduces a new type {{rsize_t}}, defined to be {{size_t}} but explicitly used to hold the size of a single object.  In code that documents this purpose by using the type {{rsize_t}}, the size of an object can be checked to verify that it is no larger than {{RSIZE_MAX}}, the maximum size of a normal single object, which provides additional input validation for library functions.  See \[[STR00-A. Use TR 24731 for remediation of existing string manipulation code]\] for additional discussion of TR 24731-1.

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

char *p = copy(9, "hi there");

The {{size_t}} type is typically represented by the same number of bits as {{int}}, that is, {{sizeof(size_t) == sizeof(int))}}.  In this case, {{n}} might be greater than {{INT_MAX}}.  The loop, however, will executes {{n}} times because the comparison {{i < n}} is an unsigned comparison. Once {{i > INT_MAX}}, {{i}} takes on negative values starting with ({{INT_MIN}}).  Consequently, the memory locations referenced by {{p\[i\]}} precede the memory referenced by {{p}} and a write-outside-array bounds occurs.

If {{size_t}} is represented by a greater number of bits than {{int}}, {{that is sizeof(size_t) > sizeof(int)}}, the same behavior occurs for values of {{n <= UINT_MAX}}. For values of {{n > UINT_MAX}} all of memory within {{\[INT_MIN, INT_MAX\]}} from the beginning of the output buffer are overwritten in an infinite loop.  This is because the expression {{\++i}} will wrap around to zero before the condition {{i < n}} ever evaluates to false.

char *copy(rsize_t n, const char *str) {
  rsize_t i;
  char *p;
  if (n > RSIZE_MAX) {
    /* Handle unreasonable object size error */
  }
  p = (char *)malloc(n);
  if (p == NULL) {
    /* Handle malloc failure */
  }
  for ( i = 0; i < n; ++i ) {
    p[i] = *str++;
  }
  return p;
}

char *p = copy(9, "hi there");

\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 7.17, "Common definitions <stddef.h>"
\[[ISO/IEC 9899-1999|AA. C References#ISO/IEC 9899-1999]\] Section 7.20.3, "Memory management functions"
\[[ISO/IEC TR 24731-1-2007|AA. C References#ISO/IEC TR 24731-1-2007]\]