空文字とかfalseとかnullとか確認

truthy_falsy.php

<?php
echo "target\tif  \tisset\tempty\tis_num\t''  \t'0' \t0   \n";
array_map(function($var){
    static $i =  0;
    $type = array("''", "0", "'0'", "false", "null");
    echo sprintf('% 6s',$type[$i++]) ."\t";
    echo (($var) ? 'true' : 'false') ."\t";
    echo (isset($var) ? 'true' : 'false') ."\t";
    echo (empty($var) ? 'true' : 'false') ."\t";
    echo (is_numeric($var) ? 'true' : 'false') ."\t";
    echo (($var == '') ? 'true' : 'false') ."\t";
    echo (($var == '0') ? 'true' : 'false') ."\t";
    echo (($var == 0) ? 'true' : 'false') ."\n";
}, array('', 0, '0', false, null));