UMBC CS 201, Fall 02
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
<![CDATA[
int StartSocialSecurity(int age, int ssn)
{
assert( age == 65 );
.
.
.
}
]]>
will produce the error message:
<![CDATA[
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() :
<![CDATA[
/* 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:
<![CDATA[
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.
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Monday, 11-Nov-2002 17:40:24 EST