Empty ();--The best use of a function.
Definition and scope: used to check if a variable has a null value: include: empty string, 0,null or FALSE, that is: "http://localhost/?fo=" or "http://localhost/?fo=0", the result of empty detection is is ture, not applicable: does not apply to the detection of a parameter that can be 0.
Is_numeric ();--only for the detection of numbers, but if the parameter name does not exist, it will be wrong, so it is not suitable for the first layer detection.
Comprehensive Example:
<?php
Ini_set ("Display_errors", 1);
Ini_set ("error_reporting", E_all); Print_r
Error_reporting (E_all);
$a =null;
if (Isset ($a)) echo ' variable $ A ' isset is true ';
Echo ' if (Isset ($_get[' fo ')) {
echo ' variable/' fo/' isset is true, variable available ';
}else{
echo ' variable/' fo/' Isset is false, no variable set ';
}
Echo ' if (Empty ($_get[' fo '))) {
echo ' variable/' fo/' empty is true, that is, null or invalid value ';
}else{
echo ' variable/' fo/' of empty is false, has value ';
}
Echo ' if (Is_numeric ($_get[' fo '))) {//There is no fo parameter in the parameter, there is an error.
echo ' variable/' fo/' is_numeric is true, is the number ';
}else{
echo ' variable/' fo/' Is_numeric is false, not a number ';
}
echo "echo ' fo no value, empty string ';
}elseif ($_get[' fo ']!= ') {
Echo ' fo has value, not for/'. ';
}
echo "if ($_get[' sex ']== ' m ') {//error occurs when there is no sex variable in the parameter.
Echo ' The man ';
}elseif ($_get[' sex ']== ' f ') {
echo ' female ';
}
?>
<! DOCTYPE HTML PUBLIC "-//W3C//DTD XHTML 1.0 transitional//en" "Http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd ">
<meta http-equiv= "Content-type" content= "text/html; charset=gb2312 "/>
<title> Untitled Document </title>
<body>
</body>
<p>
<a href= "? fo=jack" > RMS </a> <a href= "? fo=" > Null value </a> <a href= "? fo=0" > Pass 0 value </a>
<br/><br/>
<a href= "? sex=m" > Gender: Male </a> <a href= "? sex=f" > Gender: Women </a>
<br/><br/>
<a href= "/" > Empty </a>
<br/><br/>
<input type= "text" value= "<?php echo $_get[' fo ']!= '? $_get[' fo ']: ';? > "size=" 155 "/>
</p>
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