Number Systems and Base Conversion

Computers think in binary, and programmers often read numbers in hexadecimal. PHP can convert between the common number systems.

Converting from decimal

1
2
3
4

<?php
echo decbin(10) . "\n";    // binary
echo decoct(64) . "\n";    // octal
echo dechex(255);          // hexadecimal

1
2
3

1010
100
ff

Converting to decimal

1
2
3
4

<?php
echo bindec("1010") . "\n";
echo octdec("100") . "\n";
echo hexdec("ff");

1
2
3

10
64
255

Between any bases

base_convert($number, $from, $to) works for bases 2 to 36. The number is passed as a string.

1
2
3

<?php
echo base_convert("ff", 16, 2) . "\n";
echo base_convert("z", 36, 10);

1
2

11111111
35

Where you meet these

• Colours: #D95D39 is three hex numbers, one each for red, green and blue.
• File permissions: chmod("file.txt", 0644) uses octal.
• Bit flags: binary shows which options are on.

1
2
3
4
5
6

<?php
$hex = "D95D39";

[$r, $g, $b] = [hexdec(substr($hex, 0, 2)), hexdec(substr($hex, 2, 2)), hexdec(substr($hex, 4, 2))];

echo "rgb($r, $g, $b)";

1

rgb(217, 93, 57)