curl POST format for CURLOPT_POSTFIELDS

In case you are sending a string, urlencode() it. Otherwise if array, it should be key=>value paired and the Content-type header is automatically set to multipart/form-data.

Also, you don't have to create extra functions to build the query for your arrays, you already have that:

$query = http_build_query($data, '', '&');

EDIT: From php5 upwards, usage of http_build_query is recommended:

string http_build_query ( mixed $query_data [, string $numeric_prefix [,                           string $arg_separator [, int $enc_type = PHP_QUERY_RFC1738 ]]] )

Simple example from the manual:

<?php$data = array('foo'=>'bar',              'baz'=>'boom',              'cow'=>'milk',              'php'=>'hypertext processor');echo http_build_query($data) . "\n";/* output:foo=bar&baz=boom&cow=milk&php=hypertext+processor*/?>

before php5:

From the manual:

CURLOPT_POSTFIELDS

The full data to post in a HTTP "POST" operation. To post a file, prepend a filename with @ and use the full path. The filetype can be explicitly specified by following the filename with the type in the format ';type=mimetype'. This parameter can either be passed as a urlencoded string like 'para1=val1&para2=val2&...' or as an array with the field name as key and field data as value. If value is an array, the Content-Type header will be set to multipart/form-data. As of PHP 5.2.0, files thats passed to this option with the @ prefix must be in array form to work.

So something like this should work perfectly (with parameters passed in a associative array):

function preparePostFields($array) {  $params = array();  foreach ($array as $key => $value) {    $params[] = $key . '=' . urlencode($value);  }  return implode('&', $params);}

Do not pass a string at all!

You can pass an array and let php/curl do the dirty work of encoding etc.