Page History

...

Wiki Markup

In this noncompliant code example, the function {{clear()}} zeros the elements in an array. The function has one parameter declared as {{int array\[\]}} and is passed a static array consisting of twelve12 {{int}} as the argument. The function {{clear()}} uses the idiom {{sizeof(array) / sizeof(array\[0\])}} to determine the number of elements in the array.  However, {{array}} has a pointer type because it is a parameter. As a result, {{sizeof(array)}} is {{sizeof(int \*)}}. For example, on an architecture (such as IA-32) where the {{sizeof(int) == 4}} and the {{sizeof(int *) == 4}}, the expression {{sizeof(array) / sizeof(array\[0\])}} evaluates to 1, regardless of the length of the array passed, leaving the rest of the array unaffected.

Code Block

bgColor	#FFcccc

void clear(int array[]) {
  for (size_t i;
  for (i = 0; i < sizeof(array) / sizeof(array[0]); ++i) {
     array[i] = 0;
   }
}

void dowork(void) {
  int dis[12];

  clear(dis);
  /* ... */
}

...

Code Block

bgColor	#ccccff

void clear(int array[], size_t len) {
  size_t i;
  for (size_t i = 0; i < len; i++) {
     array[i] = 0;
  }
}

void dowork(void) {
  int dis[12];

  clear(dis, sizeof(dis) / sizeof(dis[0]));
  /* ... */
}

...

Space shortcuts

Page tree

Versions Compared

Old Version 54

New Version 55

Key