ord()

(PHP 4, PHP 5, PHP 7)

转换字符串第一个字节为 0-255 之间的值

说明

ord (string $string ) : int

解析 $string 二进制值第一个字节为 0 到 255 范围的无符号整型类型。

如果字符串是 ASCII、 ISO-8859、Windows 1252之类单字节编码，就等于返回该字符在字符集编码表中的位置。 但请注意，本函数不会去检测字符串的编码，尤其是不会识别类似 UTF-8 或 UTF-16 这种多字节字符的 Unicode 代码点（code point）。

该函数是 chr() 的互补函数。

参数

$string

一个字符。

返回值

返回 0 - 255 的整型值。

范例

ord() 范例

 <?php
$str = "\n";
if (ord($str) == 10) {
    echo "The first character of \$str is a line feed.\n";
}
?>  

检查 UTF-8 字符串的每一个字节

 <?php
declare(encoding='UTF-8');
$str = "";
for ( $pos=0; $pos < strlen($str); $pos ++ ) {
 $byte = substr($str, $pos);
 echo 'Byte ' . $pos . ' of $str has value ' . ord($byte) . PHP_EOL;
}
?>  

以上例程会输出：

参见

• chr()返回指定的字符
• » ASCII 码表

 As ord() doesn't work with utf-8, and if you do not have access to mb_* functions, the following function will work well:
<?php
function ordutf8($string, &$offset) {
  $code = ord(substr($string, $offset,1)); 
  if ($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;
}
?>
$offset is a reference, as it is not easy to split a utf-8 char-by-char. Useful to iterate on a string:
<?php
$text = "abcàê߀abc";
$offset = 0;
while ($offset >= 0) {
  echo $offset.": ".ordutf8($text, $offset)."\n";
}
/* returns:
0: 97
1: 98
2: 99
3: 224
5: 234
7: 223
9: 8364
12: 97
13: 98
14: 99
*/
?>
Feel free to adapt my code to fit your needs. 

 Regarding character sets, and whether or not this is "ASCII". Firstly, there is no such thing as "8-bit ASCII", so if it were ASCII it would only ever return integers up to 127. 8-bit ASCII-compatible encodings include the ISO 8859 family of encodings, which map various common characters to the values from 128 to 255. UTF-8 is also designed so that characters representable in 7-bit ASCII are coded the same; byte values higher than 127 in a UTF-8 string represent the beginning of a multi-byte character.
In fact, like most of PHP's string functions, this function isn't doing anything to do with character encoding at all - it is just interpreting a binary byte from a string as an unsigned integer. That is, ord(chr(200)) will always return 200, but what character chr(200) *means* will vary depending on what character encoding it is *interpreted* as part of (e.g. during display).
A technically correct description would be "Returns an integer representation of the first byte of a string, from 0 to 255. For single-byte encodings such as (7-bit) ASCII and the ISO 8859 family, this will correspond to the first character, and will be the position of that character in the encoding's mapping table. For multi-byte encodings, such as UTF-8 or UTF-16, the byte may not represent a complete character."
The link to asciitable.com should also be replaced by one which explains what character encoding it is displaying, as "Extended ASCII" is an ambiguous and misleading name.