The 5th Annual China PHP Conference

# dechex

(PHP 4, PHP 5)

### Description

string dechex ( int \$number )

Returns a string containing a hexadecimal representation of the given number argument. The largest number that can be converted is 4294967295 in decimal resulting to "ffffffff".

### Parameters

number

Decimal value to convert

### Examples

Example #1 dechex() example

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

The above example will output:

```a
2f
```

### User Contributed Notes 33 notes

53
brent
10 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 //CORRECTBUT, 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 //CORRECTThis took me FOREVER to figure out, so hopefully I just saved someone some time. ```
jbleau at gmail dot com
8 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; } ?> ```
jrisken at mn dot rr dot com
11 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));}?> ```
joost at bingopaleis dot com
15 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> ```
12 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:000234zeropad("234",1);will produce:234 ```
andries at centim dot be
5 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 ```
monkyNOSPAM at phpfi dot org dot invalid
14 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); ```
allan-wegan at allan-wegan dot de
13 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. ```
mina86 at tlen dot pl
13 years ago
``` Easiest :P way to create random hex color:<?phpfunction rand_color() {    return substr('00000' . dechex(mt_rand(0, 0xffffff)), -6);}?> ```
sjaak at spoilerfreaks dot com
10 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' ```
Anonymous
12 years ago
``` If you need to generate random HEX-color, use this:<?phpfunction 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. ```
huda m elmatsani <justhuda at netscape dot net>
13 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 ;) ```
Anonymous
12 years ago
``` If you need to convert RGB-color into HEX-color, use this:<?phpfunction rgb2hex(\$rgb){    return sprintf("%06X", \$rgb);}\$hex = rgb2hex(65280); // 00FF00?> ```
delchodimi at gmail dot com
2 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));}------------------------------------------------------ ```
hugo
1 month ago
``` warning jbleau dec_to_hex method is buggy, avoid it.dec_to_hex('9900000397')-->24e16048fdec_to_hex('9900000398')-->24e16048fdec_to_hex('9900000399')-->24e16048f ```
mailderemi at gmail dot com
4 years ago
``` Javascript Crypt:<?phpfunction 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);?> ```
4 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!'; } ?> ```
Kory P.
3 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);    } ```
sneskid at hotmail dot com
5 years ago
``` If you want to create or parse signed Hex values:<?php// \$d should be an intfunction sdechex(\$d) { return (\$d<0) ? ('-' . dechex(-\$d)) : dechex(\$d); }// \$h should be a stringfunction 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() ```
9381904 at gmail dot com
5 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 ?> ```
-1
baoquyen804 at gmail dot com
2 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?> ```
-1
jenny-schubert87 dot 1 at web dot de
2 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. ```
Mista-NiceGuy at web dot de
11 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"));?> ```
mountarreat at gmail dot com
9 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); } ?> ```
cory at lavacube dot com
11 years ago
``` A handy little function to convert HEX colour codes to "web safe" colours...<?phpfunction 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: 006699Hope this helps someone out... Happy coding. :-) ```
oliver at realtsp dot com
11 years ago
``` Warning for use on 64 bit machines! The Extra length matters!32bit machine:php -r 'echo dechex(4294967295);'output: ffffffff64bit machine:php -r 'echo dechex(4294967295);'output: ffffffffso far it is ok. But for slightly bigger numbers:32bit machine:php -r 'echo dechex(4294967296);'output: 064bit machine:php -r 'echo dechex(4294967296);'output: 100000000note the difference!This is particularly important when converting negative numbers:64bit machine:php -r 'echo dechex(-1);'output: ffffffffffffffff32bit machine:php -r 'echo dechex(-1);'output: ffffffffIf 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). ```
morten at nilsen dot com
12 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.phpandhttp://ryo-ohki.4th-age.com/demos/able.phpsdechex 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());?> ```
wangster at darkcore dot net
12 years ago
``` This function will take a string and convert it into a hexdump.e.g.3c666f6e 74207369 7a653d22 33223e4c  <font.size."3">L6561726e 20686f77 20746f20 62652061  earn.how.to.be.afunction 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;} ```
admin[TAKETHISOUT] at torsoft dot no-ip dot com
13 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;}?> ```
daevid at daevid dot com
13 years ago
``` Here's my version of a red->yellow->green gradient:<?phpfunction 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"><?phpfor (\$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"><?phpfor (\$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> ```
thr at recide dot net
13 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))); ```
jfren484 at hotmail dot com
15 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;} ```
kristoffer at caveo dot se
15 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";    //bluefor (\$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++;}?> ```