dechex

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

dechex — Decimal to hexadecimal

Description

dechex(int $num): string

Returns a string containing a hexadecimal representation of the given unsigned num argument.

The largest number that can be converted is PHP_INT_MAX * 2 + 1 (or -1): on 32-bit platforms, this will be 4294967295 in decimal, which results in dechex() returning ffffffff.

Parameters

num

The decimal value to convert.

As PHP's int type is signed, but dechex() deals with unsigned integers, negative integers will be treated as though they were unsigned.

Return Values

Hexadecimal string representation of num.

Examples

Example #1 dechex() example

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

The above example will output:

a
2f

Example #2 dechex() example with large integers

<?php
// The output below assumes a 32-bit platform.
// Note that the output is the same for all values.
echo dechex(-1)."\n";
echo dechex(PHP_INT_MAX * 2 + 1)."\n";
echo dechex(pow(2, 32) - 1)."\n";
?>

The above example will output:

ffffffff
ffffffff
ffffffff

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User Contributed Notes 34 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 ¶

22 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 ¶

19 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 ¶

20 years ago

Easiest :P way to create random hex color:

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

down

baoquyen804 at gmail dot com ¶

10 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

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

sneskid at hotmail dot com ¶

12 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

mountarreat at gmail dot com ¶

16 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

Mista-NiceGuy at web dot de ¶

18 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 ¶

19 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 ¶

22 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 ¶

16 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 ¶

9 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> ¶

21 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 ¶

12 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

hmlinks at gmail dot com ¶

12 years ago

I wrote this to convert hex into signed int, hope this helps someone out there... peace :)



<?php

$hex = dechex(-32767);

$dec = shexdex($hex);



function shexdex($hex){

    $dec = hexdec($hex);

    

    // Negative number (in binary if the msb is 1 then it is neg)

    // since one hex is 4bits, the value 8 and up contain msb of 1, hence negative number    

    if ($hex[0] >= '8'){    // Note: if you use the digit 8 it is not the same as '8'

        $dec -= 1;

        $dec = ~$dec;

        

        return -$dec;

    }

    

    return $dec;

}



if ($dec == -32767){

    echo 'Yay!';

}

?>

down

sjaak at spoilerfreaks dot com ¶

17 years ago

To force the correct usage of 32-bit unsigned integer in some functions, just add '+0'  just before processing them.



for example 

<?php echo(dechex("2724838310")); ?>

will print '7FFFFFFF'

but it should print 'A269BBA6'



When adding '+0' php will handle the 32bit unsigned integer

correctly

<?php echo(dechex("2724838310"+0)); ?>

will print 'A269BBA6'

down

allan-wegan at allan-wegan dot de ¶

21 years ago

now, here is a nice and small function to convert integers to hex strings and it avoids use of the DECHEX funtion because that function changed it's behavior too often in the past (now, in PHP version 4.3.2 it works with numbers bigger than 0x7FFFFFFF correctly, but i need to be backward compatible).

function &formatIntegerForOutput($value) {
    $text = "00000000";
    $transString = "0123456789ABCDEF";
    // handle highest nibble (nibble 7):
        $nibble = $value & 0x70000000;
        $nibble >>= 28;
        if ($value < 0) {
            $nibble = $nibble | 0x00000008;
        }
        $text[0] = $transString[$nibble];
        $value &= 0x0FFFFFFF;
    // nibbles 0 to 6:
        for ($a = 7; $a > 0; $a --) {
            $nibble = $value & 0x0000000F;
            $text[$a] = $transString[$nibble];
            $value >>= 4;
        }
    return $text
}

this function should be not too slow and is really simple.
I don't know, if the DECHEX function in the future will pad it's output to ever be 8 characters in length - so for backward compatibility reasons even in future PHP versions i avoided to use it.

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 ¶

2 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
?>

down

hugo ¶

7 years ago

warning jbleau dec_to_hex method is buggy, avoid it.

dec_to_hex('9900000397')-->24e16048f
dec_to_hex('9900000398')-->24e16048f
dec_to_hex('9900000399')-->24e16048f

down

mailderemi at gmail dot com ¶

12 years ago

Javascript Crypt:

<?php
function jsCrypt($script,$level=1){
    for ($j=0;$j<$level;$j++){
        $asc='';
        for ($i=0;$i<strlen($script);$i++)
            $asc.='%'.dechex(ord($script[$i]));
        $script='<SCRIPT LANGUAGE="JavaScript">document.write(unescape(\''.$asc.'\'));</SCRIPT>';
    }
    return $script;
}

echo jsCrypt('<script>alert(123);</script>',1);
?>

down

jenny-schubert87 dot 1 at web dot de ¶

10 years ago

I figured out another way to do this:
if you have a very long decimal number in gmp format (you can always create a gmp number with gmp_init($numberstring), you can simply do gmp_strval($gmpnumber, 16), where $gmpnumber is your gmp number, and the 16 is the base you want to transform it to. Worked for me like a charm, also works for other bases.

down

oliver at realtsp dot com ¶

19 years ago

Warning for use on 64 bit machines! The Extra length matters!

32bit machine:
php -r 'echo dechex(4294967295);'
output: ffffffff

64bit machine:
php -r 'echo dechex(4294967295);'
output: ffffffff

so far it is ok. But for slightly bigger numbers:

32bit machine:
php -r 'echo dechex(4294967296);'
output: 0

64bit machine:
php -r 'echo dechex(4294967296);'
output: 100000000

note the difference!

This is particularly important when converting negative numbers:

64bit machine:
php -r 'echo dechex(-1);'
output: ffffffffffffffff

32bit machine:
php -r 'echo dechex(-1);'
output: ffffffff

If you want your code to be portable to amd64 or xeons (which are now quite popular with hosting companies) then you must ensure that your code copes with the different length of the result for negative numbers (and the max value, although that is probably less critical).

down

wangster at darkcore dot net ¶

20 years ago

This function will take a string and convert it into a hexdump.

e.g.

3c666f6e 74207369 7a653d22 33223e4c  <font.size."3">L
6561726e 20686f77 20746f20 62652061  earn.how.to.be.a

function hexdump($string) {
   $hex="";
   $substr = "";
   for ($i=0; $i < strlen($string) ;$i++) {
     if(!($i % 4) && $i != 0) {
       $hex .= " ";
     }
     if(!($i % 16) && $i != 0) {
       $clean = preg_replace("/[^a-zA-Z0-9!-.<>\/]/",".",$substr);
       $hex .= " ".htmlentities($clean)."\n";
       $substr = "";
     }
     $substr .=  $string[$i];
     $hex .= dechex(ord($string[$i]));
   }
   return $hex;
}

down

daevid at daevid dot com ¶

20 years ago

Here's my version of a red->yellow->green gradient:

<?php
function colorMeter($percent, $invert = false)
{
    //$percent is in the range 0.0 <= percent <= 1.0
    //    integers are assumed to be 0% - 100%
             // and are converted to a float 0.0 - 1.0
    //     0.0 = red, 0.5 = yellow, 1.0 = green
    //$invert will make the color scale reversed
    //     0.0 = green, 0.5 = yellow, 1.0 = red 
    
    //convert (int)% values to (float)
    if (is_int($percent)) $percent = $percent * 0.01;
    
    $R = min((2.0 * (1.0-$percent)), 1.0) * 255.0;
    $G = min((2.0 * $percent), 1.0) * 255.0;
    $B = 0.0;
    
    return (($invert) ? 
sprintf("%02X%02X%02X",$G,$R,$B) 
: sprintf("%02X%02X%02X",$R,$G,$B)); 
} //colorMeter
?>

and use it like this:

<TABLE BORDER=1 WIDTH="300">
<?php
for ($i = 0.0; $i <= 1.0; $i += 0.10)
{
    $RGB = colorMeter($i);
    print "<TR><TD BGCOLOR='".$RGB."'>".$i."</TD><TD>
<PRE>".$RGB."</PRE></TD></TR>\n";
}
?>
</TABLE>

<P>

<TABLE BORDER=1 WIDTH="300">
<?php
for ($i = 0; $i <= 100; $i += 10)
{
    $RGB = colorMeter(intval($i), true);
    print "<TR><TD BGCOLOR='".$RGB."'>".$i."</TD><TD>
<PRE>".$RGB."</PRE></TD></TR>\n";
}
?>
</TABLE>

down

thr at recide dot net ¶

20 years ago

/*
* RGB-Colorcodes(i.e: 255 0 255) to HEX-Colorcodes (i.e: FF00FF)
*/
function rgb2hex($rgb){
    if(!is_array($rgb) || count($rgb) != 3){
        echo "Argument must be an array with 3 integer elements";
        return false;
    }
    for($i=0;$i<count($rgb);$i++){
        if(strlen($hex[$i] = dechex($rgb[$i])) == 1){
            $hex[$i] = "0".$hex[$i];
        }
    }
    return $hex;
}
/* Example */
print_r(rgb2hex(array(10,255,255)));

down

cory at lavacube dot com ¶

19 years ago

A handy little function to convert HEX colour codes to "web safe" colours...

<?php

function color_mkwebsafe ( $in )
{
    // put values into an easy-to-use array
    $vals['r'] = hexdec( substr($in, 0, 2) );
    $vals['g'] = hexdec( substr($in, 2, 2) );
    $vals['b'] = hexdec( substr($in, 4, 2) );

    // loop through
    foreach( $vals as $val )
    {
        // convert value
        $val = ( round($val/51) * 51 );
        // convert to HEX
        $out .= str_pad(dechex($val), 2, '0', STR_PAD_LEFT);
    }

    return $out;
}

?>

Example: color_mkwebsafe('0e5c94');
Produces: 006699

Hope this helps someone out... Happy coding. :-)

down

jfren484 at hotmail dot com ¶

22 years ago

Here's a function which works for decimal values up to 9007199254740992 (hex 20000000000000).

function dec2hex($dec)
{
  $hex = ($dec == 0 ? '0' : '');

  while ($dec > 0)
  {
    $hex = dechex($dec - floor($dec / 16) * 16) . $hex;
    $dec = floor($dec / 16);
  }

  return $hex;
}

down

kristoffer at caveo dot se ¶

22 years ago

Heres a example of dec to html hex gradient. Have fun :)

//Amount of gradients
$l = 20;

//Start color
$start[0] = "255";     //red
$start[1] = "0";     //green
$start[2] = "255";     //blue

//End color
$end[0] = "255";     //red
$end[1] = "255";    //green
$end[2] = "255";    //blue

for ($t = 1; $t < $l;) {

    $x = $x * $t;

    for ($i = 0; $i < 3;) {

        $buffer[$i] = $start[$i] - $end[$i];
        $buffer[$i] = floor($buffer[$i] / $l);
        $rgb[$i] = $start[$i] - ($buffer[$i] * $t);

        if ($rgb[$i] > 255) {

            $rgb[$i] = 255;

        }

        $rgb[$i] = dechex($rgb[$i]);
        $rgb[$i] = strtoupper($rgb[$i]);

        if (strlen($rgb[$i]) < 2) {

            $rgb[$i] = "0$rgb[$i]";

        }

        $i++;

    }

    $color = "$rgb[0]$rgb[1]$rgb[2]";
    echo "$color";
        $t++;

}

?>

down

morten at nilsen dot com ¶

19 years ago

I see a lot of less-than-optimal functions posted on this page, so I feel I have to give some better examples... 
due to the sheer size of this collection, I have made it available on my server, rather than copy/paste it into these comments.

http://ryo-ohki.4th-age.com/demos/able.php
and
http://ryo-ohki.4th-age.com/demos/able.phps

dechex replacement function from above source:
<?php
  define('BIT_BYTE', 8); // bits per byte
  define('HEX_BYTE', BIT_BYTE/4); // hex digits in a byte

  define('BIT_INT',  32); // sizeof(int)
  define('HEX_INT',  BIT_INT / (BIT_BYTE/HEX_BYTE)); // hex digits in an int

  function i2h($int, $group=HEX_BYTE, $size=HEX_INT, $sep=' ') {
    $ret = '';
    while($size--) {
      $n=($int>>($size*4)) & 0xf;
      $ret .= $n>9?chr(55 + $n):$n;
      if($size && $size%$group == 0) $ret .= $sep;
    }
    return $ret;
  }

  echo i2h(rand(1,2)==1?-mt_rand():mt_rand());
?>

down

admin[TAKETHISOUT] at torsoft dot no-ip dot com ¶

20 years ago

<?php
/*
here are two functions, some might find them useful (maybe for encoding) 
converting string to hex and hex to string:
*/

function strhex($string)
{
    $hex="";
    for ($i=0;$i<strlen($string);$i++)
        $hex.=(strlen(dechex(ord($string[$i])))<2)? "0".dechex(ord($string[$i])): dechex(ord($string[$i]));
    return $hex;
}
function hexstr($hex)
{
    $string="";
    for ($i=0;$i<strlen($hex)-1;$i+=2)
        $string.=chr(hexdec($hex[$i].$hex[$i+1]));
    return $string;
}
?>

down

-1

9381904 at gmail dot com ¶

13 years ago

for mac address

<?php

function dec2mac($mac) {

   $mac=preg_split("([.])", $mac, 6);

   $hexmac="";

   foreach ($mac as $part) 

   {

   $part=dechex($part);

   strlen($part)<2 ? $hexmac.="0$part" : $hexmac.=$part;

   }

   return $hexmac;

} 

echo dec2mac("0.29.96.71.60.137"); // 001d60473c89

?>

down

-3

Kory P. ¶

11 years ago

Or you could use this for an RGBA color.
    function toAlphaColor($n,$a)
    {
        $rgb = substr("000000".dechex($n),-6);
        $alpha = substr("00".dechex($a),-2);
        return("#".$rgb.$alpha);
    }

＋add a note

dechex

Description

Parameters

Return Values

Examples

See Also

Found A Problem?

User Contributed Notes 34 notes