int ord ( string $string )
//Returns the ASCII value of the first character of string.
//返回字符串 string 第一个字符的 ASCII 码值。
//This function complements chr().
//该函数是 chr() 的互补函数。

<?php
/**
 * Created by PhpStorm.
 * User: zhangrongxiang
 * Date: 2018/2/18
 * Time: 下午9:43
 */
$str = 'abcdef';

for ( $i = 0; $i < strlen( $str ); $i ++ ) {
    echo $str[ $i ] . ' : ' . ord( $str{$i} ) . PHP_EOL;
}
/*
 * a : 97
 * b : 98
 * c : 99
 * d : 100
 * e : 101
 * f : 102
 */

echo ord( 'a' ) . PHP_EOL;//97
echo ord( 'b' ) . PHP_EOL;//98

function ordutf8( $string, &$offset ) {
    $code        = ord( substr( $string, $offset, 1 ) );
    $bytesnumber = 0;
    if ( $code >= 128 ) {        //otherwise 0xxxxxxx
        if ( $code < 224 ) {
            $bytesnumber = 2;
        }                //110xxxxx
        else if ( $code < 240 ) {
            $bytesnumber = 3;
        }        //1110xxxx
        else if ( $code < 248 ) {
            $bytesnumber = 4;
        }    //11110xxx
        $codetemp = $code - 192 - ( $bytesnumber > 2 ? 32 : 0 ) - ( $bytesnumber > 3 ? 16 : 0 );
        for ( $i = 2; $i <= $bytesnumber; $i ++ ) {
            $offset ++;
            $code2    = ord( substr( $string, $offset, 1 ) ) - 128;        //10xxxxxx
            $codetemp = $codetemp * 64 + $code2;
        }
        $code = $codetemp;
    }
    $offset += 1;
    if ( $offset >= strlen( $string ) ) {
        $offset = - 1;
    }
    
    return $code;
}

$text   = "中国??";
$offset = 0;
while ( $offset >= 0 ) {
    //0: 20013
    //3: 22269
    //6: 128516
    echo $offset . ": " . ordutf8( $text, $offset ) . PHP_EOL;
}

function uniord( $u ) {
    $k  = mb_convert_encoding( $u, 'UCS-2LE', 'UTF-8' );
    $k1 = ord( substr( $k, 0, 1 ) );
    $k2 = ord( substr( $k, 1, 1 ) );
    
    return $k2 * 256 + $k1;
}

echo uniord( "中" ) . PHP_EOL;//20013
echo uniord( "国" ) . PHP_EOL;//22269
//error
echo uniord( '??' ) . PHP_EOL;//63