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dl> <assert_options
[edit] Last updated: Sat, 12 May 2012

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(PHP 4, PHP 5)

assertChecks if assertion is FALSE


bool assert ( mixed $assertion )

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)



The assertion.

Return Values

FALSE if the assertion is false, TRUE otherwise.


Example #1 Handle a failed assertion with a custom handler

// Active assert and make it quiet

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

// Set up the callback

// Make an assertion that should fail

See Also

dl> <assert_options
[edit] Last updated: Sat, 12 May 2012
add a note add a note User Contributed Notes assert
uramihsayibok, gmail, com 20-Jun-2010 08:48
There's a nice advantage to giving assert() some code to execute, as a string, rather than a simple true/false value: commenting.


('is_int($int) /* $int parameter must be an int, not just numeric */');

// and my personal favorite
assert('false /* not yet implemented */');


The comment will show up in the output (or in your assertion handler) and doesn't require someone debugging to go through your code trying to figure out why the assertion happened. That's no excuse to not comment your code, of course.

You need to use a block comment (/*...*/) because a line comment (//...) creates an "unexpected $end" parse error in the evaluated code. Bug? Could be.
(You can get around it with "false // not yet implemented\n" but that screws up the message)
hodgman at ali dot com dot au 28-Jul-2008 04:19
As noted on Wikipedia - "assertions are primarily a development tool, they are often disabled when a program is released to the public." and "Assertions should be used to document logically impossible situations and discover programming errors— if the 'impossible' occurs, then something fundamental is clearly wrong. This is distinct from error handling: most error conditions are possible, although some may be extremely unlikely to occur in practice. Using assertions as a general-purpose error handling mechanism is usually unwise: assertions do not allow for graceful recovery from errors, and an assertion failure will often halt the program's execution abruptly. Assertions also do not display a user-friendly error message."

This means that the advice given by "gk at proliberty dot com" to force assertions to be enabled, even when they have been disabled manually, goes against best practices of only using them as a development tool.
Krzysztof &#39;ChanibaL&#39; Bociurko 01-Oct-2007 01:13
Note that func_get_args() should be used carefully and never in a string! For example:

function asserted_normal($a, $b) {
asserted_string($a, $b) {

<?php asserted_normal(1,2) ?> prints
array(2) {

but <?php asserted_string(3,4) ?> prints
array(1) {
  string(25) "var_dump(func_get_args())"

This is because of that the string passed to assert() is being evaled inside assert, and not your function. Also, note that this works correctly, because of the eval scope:

function asserted_evaled_string($a, $b) {
array(2) {

(oh, and for simplicity's sake the evaled code doesn't return true, so  don't worry that it fails assertion...)
mail<at> 13-Sep-2006 05:51
Here is a simple demonstration of Design By Contract with PHP


assert_options(ASSERT_WARNING, 0);
assert_options(ASSERT_BAIL, 1);
assert_options(ASSERT_CALLBACK, 'dcb_callback');

dcb_callback($script, $line, $message) {
"<h1>Condition failed!</h1><br />
        Script: <strong>
$script</strong><br />
        Line: <strong>
$line</strong><br />
        Condition: <br /><pre>

// Parameters
$a = 5;
$b = 'Simple DCB with PHP';

// Pre-Condition
    is_integer($a) &&
    ($a > 0) &&
    ($a < 20) &&
    is_string($b) &&
    (strlen($b) > 5);

// Function
function combine($a, $b) {
"Kombined: " . $b . $a;

$result = combine($a, $b);

// Post-Condition
    is_string($result) &&
    (strlen($result) > 0);

// All right, the Function works fine

gk at proliberty dot com 26-Aug-2005 02:35
If you expect your code to be able to work well with other code, then you should not make any assumptions about the current state of assert_options() flags, prior to calling assert(): other code may disable ASSERT_ACTIVE, without you knowing it - this would render assert() useless!

To avoid this, ALWAYS set assert_options() IMMEDIATELY before calling assert(), per the C++ paradigm for assertion usage:

In one C++ source file, you can define and undefine NDEBUG multiple times, each time followed by #include <cassert>, to enable or disable the assert macro multiple times in the same source file.

Here is how I workaround this issue in my PHP code:

/// phpxAssertHandler_f
 * @desc     Handler which also sets up assert options if not being called as handler
                 Always fatal when assertion fails
                 Always make sure assertion is enabled
                 Cannot depend on other code not using assert or using its own assert handler!
            // customize error level of assertion (php assert_options() only allows E_WARNING or nothing at all):
            // control assertion active state: not dependent on anything another piece of code might do with ASSERT_ACTIVE
            // use alternate assertion callback function:
            // NOTE: pass null as custom options parameter to use default options
            // NOTE: pass no values for assert options parameter array elements to use default options
 * @param   mixed = file or options
 * @param   line
 * @param   code
 * @return   void
function phpxAssertHandler_f($file_or_custom_options=null, $line_or_assert_options=null, $code=null){

$debug = false;

    if (
// set default assert_options
$assert_options[]=0;//ASSERT_WARNING -

        // set default custom_options
$custom_options[]=E_USER_ERROR;// error level           

if (!is_null($line_or_assert_options)){
// assert_options are passed in
if (!is_array($line_or_assert_options)){
            foreach (
$line_or_assert_options as $i=>$assert_option){
                if (
$assert_option===true) $assert_option=1;
                if (
$assert_option===false) $assert_option=0;
$debug) echo ("assert_options[$i]=$assert_option\n");

        if (!
// custom_options are passed in
if (!is_array($file_or_custom_options)){
            foreach (
$file_or_custom_options as $i=>$custom_option){
                if (
$custom_option===true) $custom_option=1;
                if (
$custom_option===false) $custom_option=0;
$debug) echo ("custom_options[$i]=$custom_option\n");

// set assert options
@assert_options (ASSERT_ACTIVE, $assert_options[0]);
assert_options (ASSERT_WARNING, $assert_options[1]);
assert_options (ASSERT_QUIET_EVAL, $assert_options[2]);
assert_options (ASSERT_CALLBACK, $assert_options[3]);        

    } else {
// we are acting as a callback function
$file = $file_or_custom_options;
$line = $line_or_assert_options;
$msg="ASSERTION FAILED: $code";
phpxErrorHandler_f ($custom_options[0],$msg,$file,$line);
nyk at forumone dot com 26-Aug-2002 01:56
Assertion is a useful debugging feature, but for building unit tests and automated regression tests you should seriously consider using the PHPtest in the PEAR archive ( that is based on the JUnit framework for Java. There is also another unit testing framework, also based on JUnit and also called PHPunit on SourceForge ( I believe it is an independent effort from that on PEAR.

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