dechex

(PHP 4, PHP 5, PHP 7, PHP 8)

dechex — 10 進数を 16 進数に変換する

説明

dechex(int $num): string

num で指定した符号なし整数値を 16 進数表現した文字列を返します。

変換できる最大の数字は、32 ビットプラットフォームの場合は PHP_INT_MAX * 2 + 1 (-1) です。これは 10 進数で表すと 4294967295 であり、 dechex() が返す結果は ffffffff になります。

パラメータ

num

変換したい 10 進数値。

PHP の int は符号付き整数ですが、 dechex() ではこれを符号なし整数として扱います。つまり、負の整数を渡しても、それを符号なし整数として処理します。

戻り値

num を 16 進文字列で表した値を返します。

例

例1 dechex() の例

<?php
echo dechex(10) . "\n";
echo dechex(47);
?>

上の例の出力は以下となります。

a
2f

例2 dechex() での大きな整数の例

<?php
// 以下の出力例は 32 ビットプラットフォームでのものです。
// すべての結果が同じになることに注目しましょう。
echo dechex(-1)."\n";
echo dechex(PHP_INT_MAX * 2 + 1)."\n";
echo dechex(pow(2, 32) - 1)."\n";
?>

上の例の出力は以下となります。

ffffffff
ffffffff
ffffffff

参考

hexdec() - 16 進数を 10 進数に変換する
decbin() - 10 進数を 2 進数に変換する
decoct() - 10 進数を 8 進数に変換する
base_convert() - 数値の基数を任意に変換する

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User Contributed Notes 17 notes

down

brent ¶

18 years ago

Be very careful calling dechex on a number if it's stored in a string.

For instance:

The max number it can handle is 4294967295 which in hex is FFFFFFFF, as it says in the documentation.

dechex(4294967295) => FFFFFFFF //CORRECT

BUT, if you call it on a string of a number, it casts to int, and automatically gives you the largest int it can handle.

dechex('4294967295') => 7FFFFFFF //WRONG!

so you'll need to cast to a float:

dechex((float) '4294967295') => FFFFFFFF //CORRECT

This took me FOREVER to figure out, so hopefully I just saved someone some time.

down

joost at bingopaleis dot com ¶

23 years ago

Here are two functions that will convert large dec numbers to hex and vice versa. And I really mean LARGE, much larger than any function posted earlier.

<pre>
// Input: A decimal number as a String.
// Output: The equivalent hexadecimal number as a String.
function dec2hex($number)
{
    $hexvalues = array('0','1','2','3','4','5','6','7',
               '8','9','A','B','C','D','E','F');
    $hexval = '';
     while($number != '0')
     {
        $hexval = $hexvalues[bcmod($number,'16')].$hexval;
        $number = bcdiv($number,'16',0);
    }
    return $hexval;
}

// Input: A hexadecimal number as a String.
// Output: The equivalent decimal number as a String.
function hex2dec($number)
{
    $decvalues = array('0' => '0', '1' => '1', '2' => '2',
               '3' => '3', '4' => '4', '5' => '5',
               '6' => '6', '7' => '7', '8' => '8',
               '9' => '9', 'A' => '10', 'B' => '11',
               'C' => '12', 'D' => '13', 'E' => '14',
               'F' => '15');
    $decval = '0';
    $number = strrev($number);
    for($i = 0; $i < strlen($number); $i++)
    {
        $decval = bcadd(bcmul(bcpow('16',$i,0),$decvalues[$number{$i}]), $decval);
    }
    return $decval;
}
</pre>

down

jrisken at mn dot rr dot com ¶

20 years ago

A less elegant but (perhaps) faster way to pad is with substr with a negative length argument. I use it in this tiny function which formats computed rgb color codes for style sheets:
<?
function toColor($n)
{
return("#".substr("000000".dechex($n),-6));
}
?>

down

mina86 at tlen dot pl ¶

21 years ago

Easiest :P way to create random hex color:

<?php
function rand_color() {
    return substr('00000' . dechex(mt_rand(0, 0xffffff)), -6);
}
?>

down

Anonymous ¶

20 years ago

If you need to generate random HEX-color, use this:
<?php
function random_hex_color(){
    return sprintf("%02X%02X%02X", mt_rand(0, 255), mt_rand(0, 255), mt_rand(0, 255));
}
$hex = random_hex_color(); // 09B826
?>

Enjoy.

down

baoquyen804 at gmail dot com ¶

11 years ago

this base function convert string rgb to color
<?php
    function rgb_to_color($rgb, $symbols=' '){
        $color = '';
        $arr = explode($symbols, $rgb);
        $count = count($arr);
        for($i=0; $i<$count; $i++){
            $color .= dechex($arr[$i]);
        }
        return '#'.$color;
    }
       echo rgb_to_color('186 186 18');  // #baba12
    echo rgb_to_color('186-186-18', '-');  // #baba12
?>

down

sneskid at hotmail dot com ¶

13 years ago

If you want to create or parse signed Hex values:

<?php
// $d should be an int
function sdechex($d) { return ($d<0) ? ('-' . dechex(-$d)) : dechex($d); }

// $h should be a string
function shexdec($h) { return ($h[0] === '-') ? -('0x' . substr($h,1) + 0) : ('0x' . $h + 0); }

// test

$v = sdechex(-123); // string(3) "-7b"
$i = shexdec($v);   // int(-123)
var_dump($v, $i);
?>

Also note that ('0x' . $str + 0) is faster than hexdec()

down

Mista-NiceGuy at web dot de ¶

19 years ago

These are functions to convert roman numbers (e.g. MXC) into dec and vice versa.
Note: romdec() does not check whether a string is really roman or not. To force a user-input into a real roman number use decrom(romdec($input)). This will turn XXXX into XL for example.

<?php
    function decrom($dec){
        $digits=array(
            1 => "I",
            4 => "IV",
            5 => "V",
            9 => "IX",
            10 => "X",
            40 => "XL",
            50 => "L",
            90 => "XC",
            100 => "C",
            400 => "CD",
            500 => "D",
            900 => "CM",
            1000 => "M"
        );
        krsort($digits);
        $retval="";
        foreach($digits as $key => $value){
            while($dec>=$key){
                $dec-=$key;
                $retval.=$value;
            }
        }
        return $retval;
    }

    function romdec($rom){
        $digits=array(
            "I" => 1,
            "V" => 5,
            "X" => 10,
            "L" => 50,
            "C" => 100,
            "D" => 500,
            "M" => 1000
        );
        $retval="";
        $chars=array();
        for($i=1;$i<=strlen($rom);$i++){
            $chars[]=substr($rom,$i-1,1);
        }
        $step=1;
        for($i=count($chars)-1;$i>=0;$i--){
            if(!isset($digits[$chars[$i]])){ return "Error!"; }
            if($step<=$digits[$chars[$i]]){
                $step=$digits[$chars[$i]];
                $retval+=$digits[$chars[$i]];
            }
            else{
                $retval-=$digits[$chars[$i]];
            }
        }
        return $retval;
    }

    echo decrom(romdec("XXXX"));
?>

down

admin AT bobfrank DOT org ¶

20 years ago

Here is a very small zeropadding that you can use for numbers:

function zeropad($num, $lim)
{
   return (strlen($num) >= $lim) ? $num : zeropad("0" . $num);
}

zeropad("234",6);

will produce:
000234

zeropad("234",1);

will produce:
234

down

monkyNOSPAM at phpfi dot org dot invalid ¶

23 years ago

Here's how to use bitwise operations for RGB2hex conversion. This function returns hexadesimal rgb value just like one submitted by gurke@bigfoot.com above.

function hexColor($color) {
  return dechex(($color[0]<<16)|($color[1]<<8)|$color[2]);
}

example:

$col[0] = 25;
$col[1] = 255;
$col[2] = 55;

print hexColor($col);

down

jbleau at gmail dot com ¶

17 years ago

I was confused by dechex's size limitation. Here is my solution to the problem. It supports much bigger values, as well as signs.



<?php

function dec_to_hex($dec)

{

    $sign = ""; // suppress errors

    if( $dec < 0){ $sign = "-"; $dec = abs($dec); }



    $hex = Array( 0 => 0, 1 => 1, 2 => 2, 3 => 3, 4 => 4, 5 => 5,

                  6 => 6, 7 => 7, 8 => 8, 9 => 9, 10 => 'a',

                  11 => 'b', 12 => 'c', 13 => 'd', 14 => 'e',    

                  15 => 'f' );

        

    do

    {

        $h = $hex[($dec%16)] . $h;

        $dec /= 16;

    }

    while( $dec >= 1 );

    

    return $sign . $h;

}

?>

down

delchodimi at gmail dot com ¶

10 years ago

I like the example with the bitwise operations but if the value of color[0] is less than 16 it's not accurate:
example:
color[0]: 0;
color[1]: 0;
color[2]: 255;
 function hexColor($color) {
  return dechex(($color[0]<<16)|($color[1]<<8)|$color[2]);
}
It returns "ff", which is not legit RGB color...
so my solution is to combine the function above with: 
function toColor($n)
{
return("#".substr("000000".dechex($n),-6));
}

If you gotta deal with array of rgb values this is my solution:
------------------------------------------------------
function hexColor($color) {
    $rgb = dechex(($color[0]<<16)|($color[1]<<8)|$color[2]);
    return("#".substr("000000".$rgb, -6));
}
------------------------------------------------------

down

huda m elmatsani <justhuda at netscape dot net> ¶

22 years ago

Create Random Hex Color:

function make_seed() { 
   list($usec, $sec) = explode(' ', microtime()); 
   return (float) $sec + ((double) $usec * 100000); 
} 

function rand_hex() {
   mt_srand(make_seed()); 
   $randval = mt_rand(0,255);
   //convert to hex
   return sprintf("%02X",$randval);
}

function random_color(){
   return "#".rand_hex().rand_hex().rand_hex();
}

hme ;)

down

andries at centim dot be ¶

13 years ago

If you need to convert a large number (> PHP_MAX_INT) to a hex value, simply use base_convert. For example:

base_convert('2190964402', 10, 16); // 829776b2

down

mountarreat at gmail dot com ¶

17 years ago

I was challenged by a problem with large number calculations and conversion to hex within php. The calculation exceeded unsigned integer and even float range. You can easily change it for your needs but it is, thanks to bcmath, capable of handling big numbers via string. This function will convert them to hex.



In this specific example though, since I use it for game internals that can only handle 32 bit numbers, it will truncate calculations at 8 digits. If the input is 1 for example it will be filled up with zeros. Output 00000001h.



Of course I don't claim it to be a good one, but it works for me and my purpose. Suggestions on faster code welcome!



<?php

// Turns numbers into 32-bit hex string; Fills up zeros

function lrgDec2Hex($number)

{

    $i = 0;

    $hex = array();



    while($i < 8) {

        if($number == 0) {

            array_push($hex, '0');

        }

        else {

            array_push($hex, strtoupper(dechex(bcmod($number, '16'))));

            $number = bcdiv($number, '16', 0);

        }

        $i++;

    }

    krsort($hex);

    return implode($hex);

}

?>

down

Anonymous ¶

20 years ago

If you need to convert RGB-color into HEX-color, use this:
<?php
function rgb2hex($rgb){
    return sprintf("%06X", $rgb);
}
$hex = rgb2hex(65280); // 00FF00
?>

down

mahdiyari ¶

3 years ago

Zero padded hex strings as a pair of 2 (8bit).

<?php 
function dec2hex($int) {
  $hex = dechex($int);
  if (strlen($hex)%2 != 0) {
    $hex = str_pad($hex, strlen($hex) + 1, '0', STR_PAD_LEFT);
  }
  return $hex;
}

dec2hex(2); // 02
dec2hex(10); // 0a
dec2hex(256); // 0100
?>

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