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PHP : Function Reference : URL Functions : http_build_query

http_build_query

Generate URL-encoded query string (PHP 5, PECL pecl_http:0.1.0-0.9.0)
string http_build_query ( array formdata [, string numeric_prefix [, string arg_separator]] )

Example 2568. Simple usage of http_build_query()

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<?php
$data = array('foo'=>'bar',
             'baz'=>'boom',
             'cow'=>'milk',
             'php'=>'hypertext processor');

echo http_build_query($data); // foo=bar&baz=boom&cow=milk&php=hypertext+processor
echo http_build_query($data, '', '&amp;'); // foo=bar&amp;baz=boom&amp;cow=milk&amp;php=hypertext+processor

?>

Example 2569. http_build_query() with numerically index elements.

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<?php
$data = array('foo', 'bar', 'baz', 'boom', 'cow' => 'milk', 'php' =>'hypertext processor');

echo http_build_query($data) . "\n";
echo http_build_query($data, 'myvar_');
?>

The above example will output:

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0=foo&1=bar&2=baz&3=boom&cow=milk&php=hypertext+processor
myvar_0=foo&myvar_1=bar&myvar_2=baz&myvar_3=boom&cow=milk&php=hypertext+processor

Example 2570. http_build_query() with complex arrays

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<?php
$data = array('user'=>array('name'=>'Bob Smith',
                           'age'=>47,
                           'sex'=>'M',
                           'dob'=>'5/12/1956'),
             'pastimes'=>array('golf', 'opera', 'poker', 'rap'),
             'children'=>array('bobby'=>array('age'=>12,
                                              'sex'=>'M'),
                               'sally'=>array('age'=>8,
                                              'sex'=>'F')),
             'CEO');

echo http_build_query($data, 'flags_');
?>

this will output : (word wrapped for readability)

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user%5Bname%5D=Bob+Smith&user%5Bage%5D=47&user%5Bsex%5D=M&
user%5Bdob%5D=5%2F12%2F1956&pastimes%5B0%5D=golf&pastimes%5B1%5D=opera&
pastimes%5B2%5D=poker&pastimes%5B3%5D=rap&children%5Bbobby%5D%5Bage%5D=12&
children%5Bbobby%5D%5Bsex%5D=M&children%5Bsally%5D%5Bage%5D=8&
children%5Bsally%5D%5Bsex%5D=F&flags_0=CEO
Note:

Only the numerically indexed element in the base array "CEO" received a prefix. The other numeric indices, found under pastimes, do not require a string prefix to be legal variable names.

Example 2571. Using http_build_query() with an object

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<?php
class myClass {
   var $foo;
   var $baz;

   function myClass() {
       $this->foo = 'bar';
       $this->baz = 'boom';
   }
}

$data = new myClass();

echo http_build_query($data); // foo=bar&baz=boom

?>

Code Examples / Notes » http_build_query

mqchen
To flyingmeteor,
Your function is pleasingly adequate, however, when comparing the results from your function with the results from the actual function, it has a minor defect. If one uses a special character (e.g. øæåöä) in a key in the $data array, it is not encoded by your function, but it is by the actual one.
This is easily solved by some minor edits:
<?php
if(!function_exists('http_build_query')) {
function http_build_query($data,$prefix=null,$sep='',$key='') {
$ret = array();
foreach((array)$data as $k => $v) {
$k = urlencode($k);
if(is_int($k) && $prefix != null) {
$k = $prefix.$k;
};
if(!empty($key)) {
$k = $key."[".$k."]";
};
if(is_array($v) || is_object($v)) {
array_push($ret,http_build_query($v,"",$sep,$k));
}
else {
array_push($ret,$k."=".urlencode($v));
};
};
if(empty($sep)) {
$sep = ini_get("arg_separator.output");
};
return implode($sep, $ret);
};
};
?>
Forgive my personal coding standard.

fabrizio
This is my own version that I was using for php <=4, hope that will help someone
this can accomplish a few things:
if called w/o parameters will return the current link
if called with the first parameter like:
 param1=a&param2=b
will return a link with the query string containing ONLY what is passed.
if called with the first parameter like:
 &param1=a&param2=b
will return a string with the current query string plus what is passed to the function
this function uses by default PHP_SELF, but if you pass the page will create the link with what you pass.
If pass secure(boolean), will create an https or http.
$url will be the actual domain.  This function will use a global variable if nothing is passed, but feel free to modify it to use the _SERVER variables.
$html is a boolean.  If true will create links with &amp; else just &
<?php
function create_link($query=NULL, $page=NULL, $secure=NULL, $html=NULL, $port=NULL, $url=NULL ){
if($html === NULL) $html = true;
if($url === NULL){
if($secure==true){
$url = $GLOBALS['_cfg']['secure_site'];
} else {
$url = $GLOBALS['_cfg']['url'];
}
}
if($query === NULL) $query = $_SERVER['QUERY_STRING'];
if($port === NULL && isset($_SERVER['BIBIVU-HTTPD'])){
$port === _SERVER_ADMIN_PORT;
}
if((isset($_SERVER['BIBIVU-HTTPD']) || !isset($_COOKIE[session_name()])) && $this->is_crawler()===false){
$query = $query.($query!=''?'&':'').session_name().'='.session_id();
}
if(substr($query,0,1) == '&'){
$query = $this->change_query(substr($query,1));
}
if($page === NULL) $page = $_SERVER['PHP_SELF'];
$page = str_replace('//','/',$page);
if(substr($page,0,1)=='/') $page = substr($page,1);
$newQry = array();
if($query!=''){
parse_str($query, $newQuery);
foreach($newQuery as $key => $item){
$newQry[] = $key.'='.$item;
}
}
if($html){
//I create the URL in HTML
$query = implode('&amp;', $newQry);
} else {
$query = implode('&', $newQry);
}
if(isset($_SERVER['BIBIVU-HTTPD'])){
$host = '';
} elseif(defined('_ADMIN_BIB') && _ADMIN_BIB==1){
if(isset($_SERVER['HTTPS']) && $_SERVER['HTTPS']=='on' && ($secure===NULL || $secure===true )){
$host = 'https://';
} else {
$host = 'http://';
}
if (strrpos($_SERVER['HTTP_HOST'], ':') > 0){
$host .= substr($_SERVER['HTTP_HOST'], 0, strrpos($_SERVER['HTTP_HOST'], ':'));
} else {
$host .= $_SERVER['HTTP_HOST'];
}
} else {
if($secure==true){
$host = 'https://'.$url;
} else {
$host = 'http://'.$url;
}
}
if($port==NULL){
//check the current port used
$port = $_SERVER['SERVER_PORT'];
if($port<=0) $port = 80;
}
if($port!=80 && $port!=443){
$host .=':'.$port;
}
if($page===''){
$ret = $query;
} else {
$ret = $host.'/'.$page.($query!=''?'?'.$query:'');
}
return $ret;
}
function change_query($addto_query, $queryOld = NULL){
// change the QUERY_STRING adding or changing the value passed
if ($queryOld === NULL){
$query1 = $_SERVER['QUERY_STRING'];
} else {
$query1 = $queryOld;
}
parse_str ($query1, $array1);
parse_str ($addto_query, $array2);
$newQuery = array_merge($array1, $array2);

foreach($newQuery as $key => $item){
$newQry[] = $key . '=' . $item;
}

return implode('&', $newQry);
}
?>

php dot net
This is a workaround for PHP versions < PHP5. It does not work with complex arrays, however.
<?
if (!function_exists('http_build_query')) {
function http_build_query($formdata, $numeric_prefix = "")
{
  $arr = array();
  foreach ($formdata as $key => $val)
    $arr[] = urlencode($numeric_prefix.$key)."=".urlencode($val);
  return implode($arr, "&");
}
}
?>

aidan
This functionality is now implemented in the PEAR package PHP_Compat.
More information about using this function without upgrading your version of PHP can be found on the below link:
http://pear.php.net/package/PHP_Compat

valdikss
This function is wrong for http!
arrays in http is like this:
files[]=1&files[]=2&...
but function makes like this
files[0]=1&files[1]=2&...
Here is normal function:
<?php
function cr_post($a,$b=\'\',$c=0){
if (!is_array($a)) return false;
foreach ((array)$a as $k=>$v){
if ($c) $k=$b.\"[]\"; elseif (is_int($k)) $k=$b.$k;
if (is_array($v)||is_object($v)) {$r[]=cr_post($v,$k,1);continue;}
$r[]=urlencode($k).\"=\".urlencode($v);}return implode(\"&\",$r);}
?>

ilya rudenko
Params with null value do not present in result string.
<?
$arr = array('test' => null, 'test2' => 1);
echo http_build_query($arr);
?>
will produce:
test2=1

donovan jimenez
Other languages (in my case Java) allow access to multiple values for the same GET/POST parameter without the use of the brace ([]) notation.  I wanted to use this function because it was faster than my own PHP implementation that urlencoded each part of a parameter array, but I needed to be able to send something like this to a service:
...?q=foo&q=bar
obviously http_build_query() by itself would have given me:
...?q[0]=foo&q[1]=bar
So, preg_replace to the rescue:
...
$query_string = http_build_query($params);
$query_string = preg_replace('/%5B(?:[0-9]|[1-9][0-9]+)%5D=/', '=', $query_string);
...
And I get single dimension arrays encoded how I need them. This works because the '=' character can't appear non-urlencoded except for exactly where I expect it to appear (between key / value pairs).
DISCLAIMER: this workaround was only intended for getting rid of the array notation when a parameter had multiple "simple" values. More complex structures will probably be mangled.

vlad_mustafin
My example of this function for PHP versions < PHP5 without any regular expressions, just cycles, recursion and standard functions. It can work with complex arrays or objects or both combined.
<?php
if(!function_exists('http_build_query')) {
   function http_build_query( $formdata, $numeric_prefix = null, $key = null ) {
       $res = array();
       foreach ((array)$formdata as $k=>$v) {
           $tmp_key = urlencode(is_int($k) ? $numeric_prefix.$k : $k);
           if ($key) {
               $tmp_key = $key.'['.$tmp_key.']';
           }
           if ( is_array($v) || is_object($v) ) {
               $res[] = http_build_query($v, null, $tmp_key);
           } else {
               $res[] = $tmp_key."=".urlencode($v);
           }
       }
       return implode("&", $res);
   }
}
?>

havelka
I think it doesnt :( when processing array let say from MySQL db, where array is list of rows (column - value), it generates the first "row" without indexes (post_subject=xxx&post_detail=yyy) while the other rows are indexed well ( 1[post_subject]=xxx&1[post_details]=yyy )
this causes confusion when the array is read back from this string (because the first line, without index is ignored (put to another variable than rest of the array), also count of this array says n+x (N = amount of rows in the array, X = amount of columns in the first row) which is wrong. The correct way should look like
0[post_subject]=xxx&0[post_detail]=yyy
for the first entry and then to continue with the rest

03-oct-2005 09:33
I made my very own http_build_query function quite some time ago for php 4 and below. Works exactly like the function below; but its just a bit shorter. :P
<?
function http_build_query($a,$b='',$c=0){
if (!is_array($a)) return false;
foreach ((array)$a as $k=>$v){
if ($c) $k=$b."[".$k."]"; elseif (is_int($k)) $k=$b.$k;
if (is_array($v)||is_object($v)) {$r[]=http_build_query($v,$k,1);continue;}
$r[]=$k."=".urlencode($v);
}
return implode("&",$r);
}
?>

colin guthrie
I am concerned about this function's generation of [ and ] in the variable names.
From what I can gather from http://www.faqs.org/rfcs/rfc3986.html (which I believe to be the most recent RFC on the matter), the use of square brackets is illegal here.
To be sure, always use the following:
str_replace(array('[',']'), array('%5B','%5D'), http_build_query($data));
I will also submit a bug, but thought it important to inform users.

flyingmeteor
Here is another equivalent function for users that don't have PHP5 yet, it behaves the same way as the PHP5 counterpart and has one extra parameter for added functionality.
<?php
if (!function_exists('http_build_query')) {
function http_build_query($data, $prefix='', $sep='', $key='') {
$ret = array();
foreach ((array)$data as $k => $v) {
if (is_int($k) && $prefix != null) $k = urlencode($prefix . $k);
if (!empty($key)) $k = $key.'['.urlencode($k).']';

if (is_array($v) || is_object($v))
array_push($ret, http_build_query($v, '', $sep, $k));
else array_push($ret, $k.'='.urlencode($v));
}
if (empty($sep)) $sep = ini_get('arg_separator.output');
return implode($sep, $ret);
}}
?>

vlad_mustafin
Dear anonymous, i think that your example is incorrect in some places (or at least is not flexible) and shortly only in names of variables (as $c, $k, etc.) and some spaces and line foldings  :), i can explain:
1. I think that next part of code is not wanted here:
<?if (!is_array($a)) return false;?>
because you have (array)$a in foreach! It is possible but not obligatory. Or maybe better to use trigger_error for this situation.
2. You don't use urlencode on key! It's wrong because it can have also unsafe value!
<?if ($c) $k=$b."[".$k."]"; elseif (is_int($k)) $k=$b.$k;?>
this part is wrong because $k can be integer even if $c is not empty. I can want to add numeric_prefix to all indexes in array, but your example will not allow to make it. Here using of elseif is excluded, these both conditions should exist simultaneously.
3. <?http_build_query($v,$k,1);?> - In my opinion it's a very rough error. You use second parameter (as "numeric_prefix" in my example and php manual for this function) for transfer of the current key into next iteration step of recursion. Certainly it's possible and is not of principle, but very not professionally, in my opinion. I use implicit rule: one ought not to violate function logic even inside of the same function one may only expand logic. And my <?http_build_query($v, null, $tmp_key);?> allows to add numeric_prefix to all indexes in array (see point 2), i need just to put $numeric_prefix instead of null into second parameter.
Also i want to extend my previous example because we must use ini_get('arg_separator.output') instead of '&' separator!
<?
if(!function_exists('http_build_query')) {
   function http_build_query( $formdata, $numeric_prefix = null, $key = null ) {
       $res = array();
       foreach ((array)$formdata as $k=>$v) {
           $tmp_key = urlencode(is_int($k) ? $numeric_prefix.$k : $k);
           if ($key) $tmp_key = $key.'['.$tmp_key.']';
           if ( is_array($v) || is_object($v) ) {
               $res[] = http_build_query($v, null /* or $numeric_prefix if you want to add numeric_prefix to all indexes in array*/, $tmp_key);
           } else {
               $res[] = $tmp_key."=".urlencode($v);
           }
           /*
           If you want, you can write this as one string:
           $res[] = ( ( is_array($v) || is_object($v) ) ? http_build_query($v, null, $tmp_key) : $tmp_key."=".urlencode($v) );
           */
      }
      $separator = ini_get('arg_separator.output');
      return implode($separator, $res);
  }
}
?>
All best!

pinkgothic
Be careful if you're assuming that arg_separator defaults to "&".
For me, with my xampp installation and PHP 5.2.1, this was scary:
[php.ini]
; The separator used in PHP generated URLs to separate arguments.
; Default is "&".
arg_separator.output = "&amp;"
... as it gave me a complete headache debugging something, as I expected the string length to be the length of the string my browser was displaying. I was so certain arg_separator was "&" because I'd never changed my php.ini that it took me seemingly forever to consider looking at the source code.
D'oh.
This may seem irrelevant at first (and I realise my case is an unusual way of stumbling into this issue), but since, if you run htmlspecialchars() over "&amp;", the result will be "&amp;amp;", DON'T expect a one- or two-parameter http_build_query() to return a query you still have to run through htmlspecialchars().
I suggest using the third parameter to retain your sanity.

colin guthrie
@ xangelusx
You said that "It is actually illegal to set arg_separator.output to &amp; ("and amp ;") as every character is considered a seperator according to the documentation."
I don't think this is correct. arg_separator.input maybe, but not the output. How can PHP encode my URLs (that is what this setting is used for, e.g. on URL rewriting etc.) with more than one separator?  It doesn't make sence for that variable.
I have personally used &amp; as a separate for output for years in order to create valid XHTML output via PHP.
I long ago wrote a function to do this for me, but depending on where I use the output, I sometimes want &amp; and sometimes just a plain old & (think putting the value in a href="" versus using it in a Location: header). Unfortunatly, I can see no way to deprecate my function just yet, as this built in function is lacking that distinction (an optional argument would be perfect IMO)

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