How to convert byte array to GBK encoded string in php

When developing web applications, we often need to convert between different character encodings. In PHP, we can use the iconv() function and the mb_convert_encoding() function to complete character encoding conversion. However, if we need to convert a byte array to a GBK encoded string, these two functions may not work properly.

In this article, we will explain how to convert a byte array into a GBK encoded string using a special trick in PHP. This technique may not seem intuitive, but it's very effective.

First, let’s take a look at the basic methods of handling byte arrays in PHP. In PHP, we can use the pack() function to convert an array to a byte array, and the unpack() function to convert a byte array to an array. The following is an example:

$ary = array(0x41, 0x42, 0x43, 0x44);
$bin = pack('C*', ...$ary);
// $bin = "ABCD"

$ary2 = unpack('C*', $bin);
// $ary2 = array(1 => 65, 2 => 66, 3 => 67, 4 => 68)

Here, we use the pack() function to convert an array containing 4 bytes into a string of length 4, using The unpack() function converts a string into an array containing 4 elements. This is a very basic example, but this method can be used to handle byte arrays of arbitrary lengths.

However, you may encounter some difficulties when trying to convert a byte array directly to a GBK encoded string. This is because GBK encoding uses double-byte characters, and the pack() function can only handle single-byte characters. So we need to convert each byte in the byte array to a character in GBK encoding.

To achieve this, we can use another built-in function in PHP chr(). This function converts an integer to the corresponding ASCII character. However, for double-byte characters in GBK encoding, we need to treat each byte specially. Specifically, we need to combine one byte and the next byte into a double-byte character, and then convert the double-byte character into a string in GBK encoding. Here is a sample code:

function bin2gbk($bin) {
    $len = strlen($bin);
    if ($len % 2 != 0) {
        return false;
    }
    $str = '';
    for ($i = 0; $i < $len; $i += 2) {
        $byte1 = ord($bin[$i]);
        $byte2 = ord($bin[$i+1]);
        if ($byte1 < 0x81 || $byte1 > 0xfe || $byte2 < 0x40 || $byte2 > 0xfe || $byte2 == 0x7f) {
            return false;
        }
        $char = chr($byte1) . chr($byte2);
        $str .= iconv('GBK', 'UTF-8', $char);
    }
    return $str;
}

This function accepts a byte array and converts it to a GBK encoded string. Specifically, the function first checks whether the length of the byte array is even. If not, it means that there is a single byte in the byte array and cannot be converted to GBK encoding, and the function returns false.

We then loop through each byte in the byte array, combine them into a double-byte character, and convert the double-byte character into a GBK-encoded string. Here, we need to pay attention to two points. First, we need to check whether each byte is within the GBK encoding range. Second, we need to use the iconv() function to convert double-byte characters to GBK encoded strings. This is because most characters in the GBK encoding are not ASCII characters and require special handling.

Finally, we return the converted GBK encoded string.

To summarize, converting a byte array to a GBK encoded string can sometimes be difficult. However, using the pack() function and the chr() function in PHP, we can convert each byte in the byte array into characters in GBK encoding, and Concatenate them into a string. This method may be a bit convoluted, but it is very effective and can solve many character encoding conversion problems.

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