How can I efficiently add a GET parameter with either a ? or & in PHP? -

i have add variable url. url might have variables. what's efficient way add new variable?

example urls:

http://domain.com/ http://domain.com/index.html?name=jones 

i need add: tag=xyz:

http://domain.com/?tag=xyz http://domain.com/index.html?name=jones&tag=xyz 

what's efficient way know whether prepend string ? or &?

here's version of function have far:

// arradditions looks array('key1'=>'value1','key2'=>'value2'); function appendurlquerystring($url, $arradditions) {     $arrquerystrings = array();     foreach ($arradditions $k=>$v) {         $arrquerystrings[] = $k . '=' . $v;     }     $strappend = implode('&',$arrquerystrings);     if (strpos($url, '?') !== false) {         $url .= '&' . $strappend;     } else {         $url = '?' . $strappend;     }     return $url; } 

but, looking ? in existing url problematic? example, possible url includes ? not actual queries, perhaps escaped character?

take @ php pecl's http_build_url. said doc page:

build url.

the parts of second url merged first according flags argument.

addition:

if don't have pecl installed, can jump through hoops. approach solid right until try rebuild new url. stock php (minus pecl) doesn't have reverse of parse_url(). making harder, parse_url() removes of grammar url in resulting parts array have put them in when reassemble. http_build_url() can take care of us, if available, wouldn't reading portion it's recommended. anyway, here's code:

<?php /**  * addqueryparam - given url , new params query string, return modified url  *   * @see http://us1.php.net/parse_url  * @see http://us1.php.net/parse_str  * @throws exception on bad input  * @param string $url parseable url add query params  * @param mixed $input_query_vars - string of & separated pairs of = separated key values or associative array of string keys => string values  * @return string new url  */ function addqueryparam ($url, $input_query_vars) {     // parse new parameters     if (is_string($input_query_vars)) {         parse_str($input_query_vars, $input_query_vars);     }      // ensure array of parameters available     if (!is_array($input_query_vars)) {         throw new exception(__function__ . ' expects associative array or query string second parameter.');     }      // break given url     $url_parts = parse_url($url);      // test proper url parse     if (!is_array($url_parts)) {         throw new exception(__function__ . ' expects parseable url first parameter');     }      // produce array of original query vars     $original_query_vars = array();     if (isset($url_parts['query']) && $url_parts['query'] !== '') {         parse_str($url_parts['query'], $original_query_vars);     }      // merge new params inot original     $new_query_vars = array_merge($original_query_vars, $input_query_vars);      // replace original query string     $url_parts['query'] = http_build_query($new_query_vars);      // put url grammar in place     if (!empty($url_parts['scheme'])) {         $url_parts['scheme'] .= '://';     }      if (!empty($url_parts['query'])) {         $url_parts['query'] = '?' . $url_parts['query'];     }      if (!empty($url_parts['fragment'])) {         $url_parts['fragment'] = '#' . $url_parts['fragment'];     }      // put , return     return implode('', $url_parts); }  // demo urls $url1 = 'http://domain.com/'; $url2 = 'http://domain.com/index.html?name=jones';  //some usage (i did cli) echo $url1, "\n"; echo addqueryparam($url1, 'tag=xyz'), "\n"; echo addqueryparam($url1, array('tag' => 'xyz')), "\n";  echo $url2, "\n"; echo addqueryparam($url2, 'tag=xyz'), "\n"; echo addqueryparam($url2, array('tag' => 'xyz')), "\n"; echo addqueryparam($url2, array('name' => 'foo', 'tag' => 'xyz')), "\n";