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(Created page with "{{DISPLAYTITLE: assert macro - <assert.h> - C}} The '''assert''' macro can be used to insert diagnostic tests into a program.")
 
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{{DISPLAYTITLE: assert macro - <assert.h> - C}}
 
{{DISPLAYTITLE: assert macro - <assert.h> - C}}
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The '''assert''' macro can be used to insert diagnostic tests into a program.
+
The '''assert''' macro, which is part of <[[assert.h - C|assert.h]]> can be used to insert diagnostic tests into a program.
 +
 
 +
<source lang="c">#include <assert.h>
 +
void assert(scalar expression);</source>
 +
 
 +
== Description ==
 +
When executed, if the expression is false (I.E. compares to zero), a diagnostic message is printed in an implementation-defined format to the standard error stream. Assert then calls the abort function.
 +
 
 +
The diagnostic message includes:
 +
 
 +
* The text of the argument
 +
* The name of the source file ([[__FILE__ - C|__FILE__]])
 +
* The source line number ([[__LINE__ - C|__LINE__]])
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* The name of the enclosing function ([[__func__ - C|__func__]]) ([[C99]])
 +
 
 +
If '''NDEBUG''' is defined as a macro name prior to the inclusion of <[[assert.h - C|assert.h]]>, assert gets defined as:
 +
 
 +
<source lang="c">#define assert(ignore) ((void)0)</source>
 +
 
 +
== Parameters ==
 +
{| class="wikitable"
 +
|-
 +
! Parameter !! Description
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|-
 +
| expression || The expression to be evaluated
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|}
 +
 
 +
== Returns ==
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The assert macro returns no value.
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 +
== Example ==
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<source lang="c">#include <assert.h>
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#include <stdio.h>
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int main(void)
 +
{
 +
    int i;
 +
 
 +
    for (i = 0; i < 10; i++)
 +
    {
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        printf("i = %d\n", i);
 +
        assert(i < 5);
 +
    }
 +
 
 +
    return 0;
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}</source>
 +
 
 +
Example Output:
 +
 
 +
<pre>i = 0
 +
i = 1
 +
i = 2
 +
i = 3
 +
i = 4
 +
i = 5
 +
example: example.c:11: main: Assertion `i < 5' failed.
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Aborted (core dumped)</pre>
 +
 
 +
Starting at variable i being set to zero, the loop continues until the assertion fails when i reaches 5. The program terminates by calling [[Stdlib.h/abort|abort()]] after printing the diagnostic message.
 +
 
 +
== See also ==
 +
* [[Assert.h/static_assert - C|static_assert macro]]
 +
* [[assert.h - C|<assert.h> header]]
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* [[C standard library]]
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* [[C Programming Language]]
 +
 
 +
{{DEFAULTSORT:assert - assert.h - C}}
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[[Category:C standard library]]
 +
[[Category:assert.h - C]]

Revision as of 06:42, 1 December 2013

The assert macro, which is part of <assert.h> can be used to insert diagnostic tests into a program. 

#include <assert.h>
void assert(scalar expression);

Description

When executed, if the expression is false (I.E. compares to zero), a diagnostic message is printed in an implementation-defined format to the standard error stream. Assert then calls the abort function.

The diagnostic message includes:

  • The text of the argument
  • The name of the source file (__FILE__)
  • The source line number (__LINE__)
  • The name of the enclosing function (__func__) (C99)

If NDEBUG is defined as a macro name prior to the inclusion of <assert.h>, assert gets defined as: 

#define assert(ignore) ((void)0)

Parameters

Parameter Description
expression The expression to be evaluated

Returns

The assert macro returns no value.

Example

#include <assert.h>
#include <stdio.h>

int main(void)
{
    int i;

    for (i = 0; i < 10; i++)
    {
        printf("i = %d\n", i);
        assert(i < 5);
    }

    return 0;
}

Example Output: 

i = 0
i = 1
i = 2
i = 3
i = 4
i = 5
example: example.c:11: main: Assertion `i < 5' failed.
Aborted (core dumped)

Starting at variable i being set to zero, the loop continues until the assertion fails when i reaches 5. The program terminates by calling abort() after printing the diagnostic message.

See also

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