Question

i am trying a piece of code.

<?php
$tmp = ord('F'); //gives the decimal value of character F (equals 70)
$tmp = $tmp - 55; //gives 15 - decimal equivalent of 0x0F
$tmp = dechex($tmp); // converts 15 to 0x0F
$fp = fopen("testing.data","wb+");
fwrite($fp,$tmp);
fclose($fp);
?>

When i open the file called testing.data in a hex editor, i see 2 bytes written. The 2 bytes are 0x36 and 0x33.
I am expecting that only 1 byte i.e. 0x0f will be written to the file. This doesn’t happen.
Please help me out with this.

Answer 1

If you want to write the byte 0x0f to the file, simply write the character with that ASCII code. You effectively want to undo ord, and the reverse function is chr:

<?php
$tmp = ord('F'); //gives the decimal value of character F (equals 70)
$tmp = $tmp - 55; //gives 15 - decimal equivalent of 0x0F
$tmp = chr($tmp); // converts 15 to a character
$fp = fopen("testing.data","wb+");
fwrite($fp,$tmp);
fclose($fp);
?>