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(shè)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(shù)，此函數(shù)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(shè)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(shè)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...