原型
_mb_substr( $str, $start, $length = null, $encoding = null )
源文件
路径:wp-includes/compat.php
<?php
...
* @param int|null $length Optional. Maximum number of characters to extract from `$str`.
* Default null.
* @param string|null $encoding Optional. Character encoding to use. Default null.
* @return string Extracted substring.
*/
function mb_substr( $str, $start, $length = null, $encoding = null ) {
return _mb_substr( $str, $start, $length, $encoding );
}
endif;
/**
* Internal compat function to mimic mb_substr().
*
* Only understands UTF-8 and 8bit. All other character sets will be treated as 8bit.
* For $encoding === UTF-8, the $str input is expected to be a valid UTF-8 byte sequence.
* The behavior of this function for invalid inputs is undefined.
*
* @ignore
* @since 3.2.0
*
* @param string $str The string to extract the substring from.
* @param int $start Position to being extraction from in `$str`.
* @param int|null $length Optional. Maximum number of characters to extract from `$str`.
* Default null.
* @param string|null $encoding Optional. Character encoding to use. Default null.
* @return string Extracted substring.
*/
function _mb_substr( $str, $start, $length = null, $encoding = null ) {
if ( null === $encoding ) {
$encoding = get_option( 'blog_charset' );
}
/*
* The solution below works only for UTF-8, so in case of a different
* charset just use built-in substr().
*/
if ( ! in_array( $encoding, array( 'utf8', 'utf-8', 'UTF8', 'UTF-8' ) ) ) {
return is_null( $length ) ? substr( $str, $start ) : substr( $str, $start, $length );
}
if ( _wp_can_use_pcre_u() ) {
// Use the regex unicode support to separate the UTF-8 characters into an array.
preg_match_all( '/./us', $str, $match );
...
?>
其他
英文文档:https://developer.wordpress.org/reference/functions/_mb_substr/