UMBC CMSC 201

UMBC CS 201, Fall 06

Assert() statements

Assert() statements can help you narrow down where your problems are happening. An assert() statement contains a condition as a parameter. If the condition is false, assert() prints out a helpful message telling you what file and what line number is causing the problem, and then quits your program. For example, the code int StartSocialSecurity(int age, int ssn) { assert( age == 65 ); . . . } will produce the error message: Assertion failed: age == 65, file security.c, line xx if, at that point in your code, the variable age wasn't 65.

Here's an example of using assert() :


/* assert.c:  This program demonstrates
 * the use of the assert() utility
 */
#include <assert.h>
#include <stdio.h>

main()
{
   int i, num_lines = 0;

   /* Count to 100 by 2's */
   for(i = 0; i != 100; i += 2)
   {
      /* print a pattern*/
      printf("~\\/~\\/");
      if(i % 15 == 0)
      {
         printf("~\n");
         /* count the number of lines*/
         i++;
      }
      /* something's wrong: make sure  */
      /* it's doing what I think it is */
      assert(i < 101);
   }

   return 0;
}

Output:

linux3[83] % a.out ~\/~\/~ ~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~ ~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~ ~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~ ~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~ ~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~ ~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/~ a.out: sample.c:24: main: Assertion `i < 101' failed. ~\/~\/~\/~\/~\/~\/~\/~\/~\/~\/Abort linux3[84] % Assert statements should never be left in code. They should only be used for debugging. There are much more graceful ways to exit a program than this.

Tuesday, 22-Aug-2006 07:14:16 EDT