在PHP中用Hex字符串写二进制数据

Question

I'm trying to write a binary file from hex string. For example, if my hex string is C27EF0EC, then the hex file should contain ASCII characters for C2, 7E, F0 and EC.
How do I do this in PHP?

Here's what I've tried:

$s="";
for ($i=0; $i<count($h); $i++) {
    $s+=pack("C*", "0x".$h[$i]);
}
$f2=fopen("codes0", "wb+");
fwrite($f2, $s);

Answer 1

So the first thing you need to do is turn your single string into an array of two-character strings with str_split.

$hex_bytes = str_split($h, 2);

Then you want to convert each of those values from a hexadecimal string to the corresponding number with hexdec.

$code_array = array_map(hexdec, $hex_bytes);

Then you want the byte value corresponding to each of those character codes, which you can get with chr:

$char_array = array_map(chr, $code_array);

Finally, you want to join all those bytes together into a single string, which you can do with implode.

$s = implode($char_array);

You can use the steps above in that order, or you can put it all together into one expression like this:

$s = implode(array_map(chr, array_map(hexdec, str_split($h,2))));

Note that as soon as you get a value above 0x7F it's no longer "ASCII".