In PHP 5.5 and above, getting the error message is as simple as:
<?php
echo array_flip(get_defined_constants(true)['pcre'])[preg_last_error()];
(PHP 5 >= 5.2.0, PHP 7)
preg_last_error — Returns the error code of the last PCRE regex execution
Returns the error code of the last PCRE regex execution.
Example #1 preg_last_error() example
<?php
preg_match('/(?:\D+|<\d+>)*[!?]/', 'foobar foobar foobar');
if (preg_last_error() == PREG_BACKTRACK_LIMIT_ERROR) {
print 'Backtrack limit was exhausted!';
}
?>
The above example will output:
Backtrack limit was exhausted!
Returns one of the following constants (explained on their own page):
PREG_NO_ERRORPREG_INTERNAL_ERRORPREG_BACKTRACK_LIMIT_ERROR (see also pcre.backtrack_limit)PREG_RECURSION_LIMIT_ERROR (see also pcre.recursion_limit)PREG_BAD_UTF8_ERRORPREG_BAD_UTF8_OFFSET_ERROR (since PHP 5.3.0)PREG_JIT_STACKLIMIT_ERROR (since PHP 7.0.0)
In PHP 5.5 and above, getting the error message is as simple as:
<?php
echo array_flip(get_defined_constants(true)['pcre'])[preg_last_error()];
Here is a more advanced function to convert an error code to text:
<?php
function preg_errtxt($errcode)
{
static $errtext;
if (!isset($errtxt))
{
$errtext = array();
$constants = get_defined_constants(true);
foreach ($constants['pcre'] as $c => $n) if (preg_match('/_ERROR$/', $c)) $errtext[$n] = $c;
}
return array_key_exists($errcode, $errtext)? $errtext[$errcode] : NULL;
}
?>
The above function pcre_error_deocde [sic] is not correct - not all of the used constants are errors constants. For example, when the error is actually PREG_BAD_UTF8_ERROR, the function outputs the text for PREG_SPLIT_OFFSET_CAPTURE.
Just an addition to my previous note: In unicode mode (with "u" modifier), PREG_BAD_UTF8_ERROR only reflects errors in the subject string. If the pattern itself contains invalid characters, preg_match() (or preg_match_all()) returns false but preg_last_error() returns 0 indicating PREG_NO_ERROR. Instead, php issues a warning: "preg_match(): Compilation failed: invalid UTF-8 string at offset 0"
here's the code to check for all errors
<?php
if (preg_last_error() == PREG_NO_ERROR) {
print 'There is no error.';
}
else if (preg_last_error() == PREG_INTERNAL_ERROR) {
print 'There is an internal error!';
}
else if (preg_last_error() == PREG_BACKTRACK_LIMIT_ERROR) {
print 'Backtrack limit was exhausted!';
}
else if (preg_last_error() == PREG_RECURSION_LIMIT_ERROR) {
print 'Recursion limit was exhausted!';
}
else if (preg_last_error() == PREG_BAD_UTF8_ERROR) {
print 'Bad UTF8 error!';
}
else if (preg_last_error() == PREG_BAD_UTF8_ERROR) {
print 'Bad UTF8 offset error!';
}
?>