摘要：檢查字符串在指定的編碼里是否有效檢查指定的字節(jié)流在指定的編碼里是否有效。它能有效避免所謂的無效編碼攻擊。要檢查的字節(jié)流。成功時返回，或者在失敗時返回。輸出空輸出編碼的字符串設置文件編碼為博客園和。

(PHP 4 >= 4.4.3, PHP 5 >= 5.1.3, PHP 7)
mb_check_encoding — Check if the string is valid for the specified encoding
mb_check_encoding — 檢查字符串在指定的編碼里是否有效

bool mb_check_encoding ([ string $var = NULL [, string $encoding = mb_internal_encoding() ]] )
// Checks if the specified byte stream is valid for the specified encoding. 
// It is useful to prevent so-called "Invalid Encoding Attack".

// 檢查指定的字節(jié)流在指定的編碼里是否有效。它能有效避免所謂的“無效編碼攻擊（Invalid Encoding Attack）”。

The byte stream to check. If it is omitted, this function checks all the input from the beginning of the request.

要檢查的字節(jié)流。如果省略了這個參數，此函數會檢查所有來自最初請求所有的輸入。

The expected encoding.

期望的編碼。

Returns TRUE on success or FALSE on failure.

成功時返回 TRUE， 或者在失敗時返回 FALSE。

 設置文件編碼為gbk*/
$str = "博客園和github。";
echo mb_check_encoding( $str, "utf-8" ) . PHP_EOL;  //輸出空
echo mb_check_encoding( $str, "gbk" ) . PHP_EOL; //輸出1

/**utf-8編碼的字符串  --> 設置文件編碼為utf-8*/
$str = "博客園和github。";
echo mb_check_encoding( $str, "utf-8" ) . PHP_EOL;  //1
echo mb_check_encoding( $str, "gbk" ) . PHP_EOL; //輸出空

$utf8Str = "我abc是誰.";
echo mb_check_encoding( $utf8Str, "utf-8" ) . PHP_EOL;  //輸出1
//如果有中文標點符號則為空！??！
echo mb_check_encoding( $utf8Str, "gbk" ) . PHP_EOL; //輸出1

/**自定義檢測字符串編碼是否為utf-8*/
function is_utf8( $str ) {
    return (bool) preg_match( "http://u", serialize($str) );
}

echo "hello 中國!" .is_utf8( "hello 中國!" ) . PHP_EOL; //1

function check_utf8( $str ) {
    $len = strlen( $str );
    for ( $i = 0; $i < $len; $i ++ ) {
        $c = ord( $str[ $i ] );
        if ( $c > 128 ) {
            if ( ( $c > 247 ) ) {
                return false;
            } elseif ( $c > 239 ) {
                $bytes = 4;
            } elseif ( $c > 223 ) {
                $bytes = 3;
            } elseif ( $c > 191 ) {
                $bytes = 2;
            } else {
                return false;
            }
            if ( ( $i + $bytes ) > $len ) {
                return false;
            }
            while ( $bytes > 1 ) {
                $i ++;
                $b = ord( $str[ $i ] );
                if ( $b < 128 || $b > 191 ) {
                    return false;
                }
                $bytes --;
            }
        }
    }
    
    return true;
} // end of check_utf8

echo check_utf8("hello 中國").PHP_EOL; // 1
echo check_utf8( "x00xE3").PHP_EOL;  //空

/** check a strings encoded value */
function checkEncoding( $string, $string_encoding ) {
    $fs = $string_encoding == "UTF-8" ? "UTF-32" : $string_encoding;
    $ts = $string_encoding == "UTF-32" ? "UTF-8" : $string_encoding;
    
    return $string === mb_convert_encoding( mb_convert_encoding( $string, $fs, $ts ), $ts, $fs );
}

/* test 1 variables */
$string   = "x00x81";
$encoding = "Shift_JIS";

/* test 1 mb_check_encoding (test for bad byte stream) */
if ( true === mb_check_encoding( $string, $encoding ) ) {
    echo "valid (" . $encoding . ") encoded byte stream!" . PHP_EOL;
} else {
    echo "invalid (" . $encoding . ") encoded byte stream!" . PHP_EOL;
}

/* test 1 checkEncoding (test for bad byte sequence(s)) */
if ( true === checkEncoding( $string, $encoding ) ) {
    echo "valid (" . $encoding . ") encoded byte sequence!" . PHP_EOL;
} else {
    echo "invalid (" . $encoding . ") encoded byte sequence!" . PHP_EOL;
}

/* test 2 */
/* test 2 variables */
$string   = "x00xE3";
$encoding = "UTF-8";
/* test 2 mb_check_encoding (test for bad byte stream) */
if ( true === mb_check_encoding( $string, $encoding ) ) {
    echo "valid (" . $encoding . ") encoded byte stream!" . PHP_EOL;
} else {
    echo "invalid (" . $encoding . ") encoded byte stream!" . PHP_EOL;
}

/* test 2 checkEncoding (test for bad byte sequence(s)) */
if ( true === checkEncoding( $string, $encoding ) ) {
    echo "valid (" . $encoding . ") encoded byte sequence!" . PHP_EOL;
} else {
    echo "invalid (" . $encoding . ") encoded byte sequence!" . PHP_EOL;
}

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