strlen函数与多字节编码的字符串字节长度

Just to remember that strlen() return the number of characters of a string. Often the strlen() function is used to compute the length in bytes of a string. This is correct until string is single byte encoded. If multi-byte char-set is used this constraint i no more verified. So when you require the number of bytes of a ASCII or UTF-8 encoded string, it is better to use following function:

/**
* Count the number of bytes of a given string.
* Input string is expected to be ASCII or UTF-8 encoded.
* Warning: the function doesn't return the number of chars
* in the string, but the number of bytes.
*
* @param string $str The string to compute number of bytes
*
* @return The length in bytes of the given string.
*/
function strBytes($str)
{
// STRINGS ARE EXPECTED TO BE IN ASCII OR UTF-8 FORMAT

// Number of characters in string
$strlen_var = strlen($str);

// string bytes counter
$d = 0;

/*
* Iterate over every character in the string,
* escaping with a slash or encoding to UTF-8 where necessary
*/
for ($c = 0; $c < $strlen_var; ++$c) {

$ord_var_c = ord($str{$d});

switch (true) {
case (($ord_var_c >= 0x20) && ($ord_var_c <= 0x7F)):
// characters U-00000000 - U-0000007F (same as ASCII)
$d++;
break;

case (($ord_var_c & 0xE0) == 0xC0):
// characters U-00000080 - U-000007FF, mask 110XXXXX
// see http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8
$d+=2;
break;

case (($ord_var_c & 0xF0) == 0xE0):
// characters U-00000800 - U-0000FFFF, mask 1110XXXX
// see http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8
$d+=3;
break;

case (($ord_var_c & 0xF8) == 0xF0):
// characters U-00010000 - U-001FFFFF, mask 11110XXX
// see http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8
$d+=4;
break;

case (($ord_var_c & 0xFC) == 0xF8):
// characters U-00200000 - U-03FFFFFF, mask 111110XX
// see http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8
$d+=5;
break;

case (($ord_var_c & 0xFE) == 0xFC):
// characters U-04000000 - U-7FFFFFFF, mask 1111110X
// see http://www.cl.cam.ac.uk/~mgk25/unicode.html#utf-8
$d+=6;
break;
default:
$d++;
}
}

return $d;
}

This function has been adapted form the JSON function used to convert character in UTF-8 representation.

With this new function we solved problem in JSON and in PEAR/SOAP php libraries.