How to tell if $query_var isset?

Question

I tired to use isset($queryvar) but that didnt work, so I implemented my own function qv_isset, but it runs into a problem when $ch is set to 0.

$cls = get_query_var('cls');
$ch = get_query_var('ch');

function qv_isset($var) {
    if($var == '') { return false; 
    } else { return true; }
}

if(qv_isset($cls) && qv_isset($ch)) {
    mcs_textbook_chapter($dialect, $cls, $ch);
} elseif(qv_isset($cls)) {              
    mcs_textbook_chapter($dialect, $cls);
} else {
    mcs_textbook($dialect);
}

Answer 1

use the indentical comparison operator:

if(get_query_var('cls') !== '' && get_query_var('ch') !== '') {
    mcs_textbook_chapter($dialect, $cls, $ch);
} elseif(get_query_var('cls') !== '') {              
    mcs_textbook_chapter($dialect, $cls);
} else {
    mcs_textbook($dialect);
}

Answer 2

You'll want to use empty, isset failed because you just set the variable. An empty value is still a value.

if ( empty($cls) && empty($ch) ){
    // Not set
}

Answer 3

If you really want to know wether a WordPress Query Var is set or not, you need to check directly for it.

All set query vars are stored into a global accessible array of the WP_Query class.

It has a default instance that is bound to the global $wp_query variable. With that in mind it is possible to create a qv_isset() function that is working precicesly:

function qv_isset($var_name) {
    $array = $GLOBALS['wp_query']->query_vars;
    return array_key_exists($var_name, $array);
}

What makes this so easy is that array_key_exists() returns true or false.

Normally to test any PHP variable if it is set or not, you can use isset(). But it has a shortcoming: If a variable is NULL, it will say that it is not set - even if it is. Comparable to what has been written about empty() here as well, it will say comparably for '' (empty string), NULL, 0 etc. .

Anyway, we do not need to rely on that function to check wether or not a queryvar has been set as we can make use of array_key_exists() here.

---

Now for your code:

function qv_get($var_name, $default = null) {
    return qv_isset($var_name) ? get_query_var($var_name) : $default;
}

mcs_textbook_chapter($dialect, qv_get('cls'), qv_get('ch'));

Or with other words: If your function already has (that many) optional parameters, take a look how you can best feed it. Unset variables are NULL (like said above with isset()), so this is useful to pass them as unset optional parameters as well.

Answer 4

Hi @imHavoc:

I might write that code like this (although there are several valid ways to write it):

$cls = get_query_var('cls');
$ch =  get_query_var('ch');

if (strlen("{$cls}{$ch}")==0) {
  mcs_textbook($dialect);
} if (strlen($ch)==0) {
  mcs_textbook_chapter($dialect, $cls);
} else {
  mcs_textbook_chapter($dialect, $cls, $ch);
}