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

    See Also

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    User Contributed Notes 34 notes

    up
    87
    brent
    17 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.
    up
    15
    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 $decval;
    }
    </pre>
    up
    8
    jrisken at mn dot rr dot com
    19 years ago
    A less elegant but (perhaps) faster way to pad is with substr with a negative length argument. I use it in this tiny function which formats computed rgb color codes for style sheets:
    <?
    function toColor($n)
    {
    return("#".substr("000000".dechex($n),-6));
    }
    ?>
    up
    4
    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);
    }
    ?>
    up
    1
    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
    ?>
    up
    4
    Anonymous
    19 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.
    up
    1
    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()
    up
    2
    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($hex);
    }
    ?>
    up
    1
    Mista-NiceGuy at web dot de
    18 years ago
    These are functions to convert roman numbers (e.g. MXC) into dec and vice versa.
    Note: romdec() does not check whether a string is really roman or not. To force a user-input into a real roman number use decrom(romdec($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"));
    ?>
    up
    4
    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
    up
    2
    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);
    up
    4
    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 . $h;
    }
    ?>
    up
    1
    delchodimi at gmail dot com
    9 years ago
    I like the example with the bitwise operations but if the value of color[0] is less than 16 it's not accurate:
    example:
    color[0]: 0;
    color[1]: 0;
    color[2]: 255;
    function hexColor($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));
    }
    ------------------------------------------------------
    up
    2
    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 ;)
    up
    3
    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
    up
    1
    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!';
    }
    ?>
    up
    1
    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'
    up
    1
    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.
    up
    1
    Anonymous
    19 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
    ?>
    up
    2
    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
    ?>
    up
    2
    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
    up
    2
    mailderemi at gmail dot com
    11 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);
    ?>
    up
    0
    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.
    up
    1
    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).
    up
    1
    wangster at darkcore dot net
    19 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;
    }
    up
    1
    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>"    .$RGB."</PRE></TD></TR>\n";
    }
    ?>
    </TABLE>
    up
    1
    thr at recide dot net
    20 years ago
    /*
    * RGB-Colorcodes(i.e: 255 0 255) to HEX-Colorcodes (i.e: FF00FF)
    */
    function rgb2hex($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)));
    up
    0
    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. :-)
    up
    1
    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;
    }
    up
    1
    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++;

    }

    ?>
    up
    0
    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());
    ?>
    up
    0
    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     $string;
    }
    ?>
    up
    -1
    9381904 at gmail dot com
    13 years ago
    for mac address
    <?php
    function dec2mac($mac) {
    $mac=preg_split("([.])", $mac, 6);
    $hexmac="";
    foreach (    $mac as $part)
    {
    $part=dechex($part);
    strlen($part)<2 ? $hexmac.="0$part" : $hexmac.=$part;
    }
    return     $hexmac;
    }
    echo     dec2mac("0.29.96.71.60.137"); // 001d60473c89
    ?>
    up
    -3
    Kory P.
    11 years ago
    Or you could use this for an RGBA color.
    function toAlphaColor($n,$a)
    {
    $rgb = substr("000000".dechex($n),-6);
    $alpha = substr("00".dechex($a),-2);
    return("#".$rgb.$alpha);
    }
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