PHP之mb_substr使用

摘要：获取部分字符串根据字符数执行一个多字节安全的操作。位置是从的开始位置进行计数。第一个字符的位置是。从该中提取子字符串。中要使用的最大字符数。如果省略，则使用内部字符编码。函数根据和参数返回中指定的部分。

(PHP 4 >= 4.0.6, PHP 5, PHP 7)
mb_substr — Get part of string
mb_substr — 获取部分字符串

string mb_substr ( 
    string $str ,
    int $start [,
    int $length = NULL [, 
    string $encoding = mb_internal_encoding() ]] 
    )
// Performs a multi-byte safe substr() operation based on number of characters. Position is counted from 
// the beginning of str. First character"s position is 0. Second character position is 1, and so on.
//根据字符数执行一个多字节安全的 substr() 操作。 位置是从 str 的开始位置进行计数。 第一个字符的位置是 0。第二个字符的位置是 1，以此类推。

The string to extract the substring from.

从该 string 中提取子字符串。

If start is non-negative, the returned string will start at the start"th position in str, counting from zero. For instance, in the string "abcdef", the character at position 0 is "a", the character at position 2 is "c", and so forth.

如果 start 不是负数，返回的字符串会从 str 第 start 的位置开始，从 0 开始计数。举个例子，字符串 "abcdef"，位置 0 的字符是 "a"，位置 2 的字符是 "c"，以此类推。

If start is negative, the returned string will start at the start"th character from the end of str.

如果 start 是负数，返回的字符串是从 str 末尾处第 start 个字符开始的。

Maximum number of characters to use from str. If omitted or NULL is passed, extract all characters to the end of the string.

str 中要使用的最大字符数。如果省略了此参数或者传入了 NULL，则会提取到字符串的尾部。

The encoding parameter is the character encoding. If it is omitted, the internal character encoding value will be used.

encoding 参数为字符编码。如果省略，则使用内部字符编码。

mb_substr() returns the portion of str specified by the start and length parameters.

mb_substr() 函数根据 start 和 length 参数返回 str 中指定的部分。

5.4.8 - Passing NULL as length extracts all characters to the end of the string. Prior to this version NULL was treated the same as 0.

 0  length > 0*/
$mystring = mb_substr( $string, 5, 1 );
echo $mystring . PHP_EOL; // 5
$mystring = mb_substr( $string, 5, 2 );
echo $mystring . PHP_EOL; // 56
$mystring = mb_substr( $string, 10, 2 );
echo $mystring . PHP_EOL; // 你好

/** start < 0  length > 0*/
$mystring = mb_substr( $string, - 2, 2 );
echo $mystring . PHP_EOL; // 你好
echo "mb_strlen : " . mb_strlen( $string ) . PHP_EOL;//12
$mystring = mb_substr( $string, - mb_strlen( $string ), 2 );
echo $mystring . PHP_EOL; // 01
$mystring = mb_substr( $string, - 3, 2 );
echo $mystring . PHP_EOL; // 9你

/** start > 0  length <  0*/
$mystring = mb_substr( $string, 5, - 1 );
echo $mystring . PHP_EOL; // 56789你
$mystring = mb_substr( $string, 0, - mb_strlen( $string ) + 1 );
echo $mystring . PHP_EOL; // 0
$mystring = mb_substr( $string, 5, - 5 );
echo $mystring . PHP_EOL; // 56

/** start < 0  length <  0*/
$mystring = mb_substr( $string, - 10, - 1 );
echo $mystring . PHP_EOL; // 23456789你
$mystring = mb_substr( $string, - 5, - 1 );
echo $mystring . PHP_EOL; // 789你

function mb_ucfirst( $str, $enc = "utf-8" ) {
    return mb_strtoupper( mb_substr( $str, 0, 1, $enc ), $enc ) . mb_substr( $str, 1, mb_strlen( $str, $enc ), $enc );
}

echo mb_ucfirst( "hello world 你好 中国" ) . PHP_EOL; //Hello world 你好 中国

/**
 * @param $string
 * @param string $encoding
 *
 * @return array
 */
function get_character_classes( $string, $encoding = "UTF-8" ) {
    $current_encoding = mb_internal_encoding();
    mb_internal_encoding( $encoding );
    $has          = array();
    $stringlength = mb_strlen( $string, $encoding );
    for ( $i = 0; $i < $stringlength; $i ++ ) {
        $c = mb_substr( $string, $i, 1 );
        if ( ( $c >= "0" ) && ( $c <= "9" ) ) {
            $has["numeric"] = "numeric";
        } else if ( ( $c >= "a" ) && ( $c <= "z" ) ) {
            $has["alpha"]      = "alpha";
            $has["alphalower"] = "alphalower";
        } else if ( ( $c >= "A" ) && ( $c <= "Z" ) ) {
            $has["alpha"]      = "alpha";
            $has["alphaupper"] = "alphaupper";
        } else if ( ( $c == "$" ) || ( $c == "£" ) ) {
            $has["currency"] = "currency";
        } else if ( ( $c == "." ) && ( $has["decimal"] ) ) {
            $has["decimals"] = "decimals";
        } else if ( $c == "." ) {
            $has["decimal"] = "decimal";
        } else if ( $c == "," ) {
            $has["comma"] = "comma";
        } else if ( $c == "-" ) {
            $has["dash"] = "dash";
        } else if ( $c == " " ) {
            $has["space"] = "space";
        } else if ( $c == "/" ) {
            $has["slash"] = "slash";
        } else if ( $c == ":" ) {
            $has["colon"] = "colon";
        } else if ( ( $c >= " " ) && ( $c <= "~" ) ) {
            $has["ascii"] = "ascii";
        } else {
            $has["binary"] = "binary";
        }
    }
    mb_internal_encoding( $current_encoding );
    
    return $has;
}

$string = "1234asdfA£^_{}|}~žščř";
foreach ( get_character_classes( $string ) as $k => $v ) {
    echo $k . " : " . $v . PHP_EOL;
}
//numeric : numeric
//alpha : alpha
//alphalower : alphalower
//alphaupper : alphaupper
//currency : currency
//ascii : ascii
//binary : binary

http://php.net/manual/en/func...