ISSET ();--suitable for detecting the existence of this parameter.
Definition and scope: used to test whether a variable has a value (including 0,false, or an empty string, but not null), that is, "http://localhost/?fo=" can also be detected and therefore does not apply. However, if the "http://localhost/" parameter does not contain the FO parameter, it can be detected with isset, at which point Isset ($_get[' fo ') returns false.
does not apply to: This function is not suitable for validating text in an HTML form. To check whether the user input text is valid, you can use empty ();
Empty ();-a function that is best used.
Definition and scope: used to check whether a variable has a null value: include: null string, 0,null or FALSE, namely: "http://localhost/?fo=" or "http://localhost/?fo=0", Empty detected results are ture, do not apply to the scope: does not apply to detect can be 0 parameters.
Is_numeric ();--Applies only to the number of detections, but if the parameter name does not exist, there will be an error, so it is not suitable for first-level detection.
Comprehensive Example:
Copy Code code as follows:
<?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 for true, variable available ';
}else{
echo ' variable/' fo/' isset is false, without variable setting ';
}
Echo ' if (Empty ($_get[' fo ')) {
The empty of the echo ' variable/' fo/' is true, i.e. null or void value ';
}else{
echo ' variable/' fo/' empty is false, has value ';
}
Echo ' if (Is_numeric ($_get[' fo ')) {///If there is no fo parameter in the argument, an error occurs.
The echo ' variable/' fo/' is_numeric is true, is the number ';
}else{
The echo ' variable/' fo/' Is_numeric is false, not a number ';
}
The case:echo ' fo no value, empty string ';
}elseif ($_get[' fo ']!= ') {
Echo ' fo has value, not for/'/'. '
}
The case of echo "if ($_get[' sex ']== ' m ') {///when there is no sex variable in the argument, an error occurs.
echo ' man ';
}elseif ($_get[' sex ']== ' f ') {
echo ' woman ';
}
?>
<! 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" > Valid value </a> <a href= "? fo=" > Null value </a> <a href= "? fo=0" > 0 value </a>
<br/><br/>
<a href= "sex=m" > Sex: Male </a> <a href= "sex=f" > Gender: Female </a>
<br/><br/>
<a href= "/" > Empty </a>
<br/><br/>
<input type= "text" value= "<?php echo $_get[' fo ']!= '" $_get[' fo ']: ';? > "size="/>
</p>
