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assert

(PHP 4, PHP 5)

assertChecks if assertion is FALSE

Description

bool assert ( mixed $assertion [, string $description ] )

assert() will check the given assertion and take appropriate action if its result is FALSE.

If the assertion is given as a string it will be evaluated as PHP code by assert(). The advantages of a string assertion are less overhead when assertion checking is off and messages containing the assertion expression when an assertion fails. This means that if you pass a boolean condition as assertion this condition will not show up as parameter to the assertion function which you may have defined with the assert_options() function, the condition is converted to a string before calling that handler function, and the boolean FALSE is converted as the empty string.

Assertions should be used as a debugging feature only. You may use them for sanity-checks that test for conditions that should always be TRUE and that indicate some programming errors if not or to check for the presence of certain features like extension functions or certain system limits and features.

Assertions should not be used for normal runtime operations like input parameter checks. As a rule of thumb your code should always be able to work correctly if assertion checking is not activated.

The behavior of assert() may be configured by assert_options() or by .ini-settings described in that functions manual page.

The assert_options() function and/or ASSERT_CALLBACK configuration directive allow a callback function to be set to handle failed assertions.

assert() callbacks are particularly useful for building automated test suites because they allow you to easily capture the code passed to the assertion, along with information on where the assertion was made. While this information can be captured via other methods, using assertions makes it much faster and easier!

The callback function should accept three arguments. The first argument will contain the file the assertion failed in. The second argument will contain the line the assertion failed on and the third argument will contain the expression that failed (if any — literal values such as 1 or "two" will not be passed via this argument). Users of PHP 5.4.8 and later may also provide a fourth optional argument, which will contain the description given to assert(), if it was set.

Parameters

assertion

The assertion.

description

An optional description that will be included in the failure message if the assertion fails.

Return Values

FALSE if the assertion is false, TRUE otherwise.

Changelog

Version Description
5.4.8 The description parameter was added. The description is also now provided to a callback function in ASSERT_CALLBACK mode as the fourth argument.

Examples

Example #1 Handle a failed assertion with a custom handler

<?php
// Active assert and make it quiet
assert_options(ASSERT_ACTIVE1);
assert_options(ASSERT_WARNING0);
assert_options(ASSERT_QUIET_EVAL1);

// Create a handler function
function my_assert_handler($file$line$code)
{
    echo 
"<hr>Assertion Failed:
        File '
$file'<br />
        Line '
$line'<br />
        Code '
$code'<br /><hr />";
}

// Set up the callback
assert_options(ASSERT_CALLBACK'my_assert_handler');

// Make an assertion that should fail
assert('mysql_query("")');
?>

Example #2 Using a custom handler to print a description

<?php
// Active assert and make it quiet
assert_options(ASSERT_ACTIVE1);
assert_options(ASSERT_WARNING0);
assert_options(ASSERT_QUIET_EVAL1);

// Create a handler function
function my_assert_handler($file$line$code$desc null)
{
    echo 
"Assertion failed at $file:$line$code";
    if (
$desc) {
        echo 
": $desc";
    }
    echo 
"\n";
}

// Set up the callback
assert_options(ASSERT_CALLBACK'my_assert_handler');

// Make an assertion that should fail
assert('2 < 1');
assert('2 < 1''Two is less than one');
?>

The above example will output:

Assertion failed at test.php:21: 2 < 1
Assertion failed at test.php:22: 2 < 1: Two is less than one

See Also

PHP Manual