PHP Web开发中常用的三个表单验证函数,这些都是一些经常用到的判断函数。
ISSET();——适合于检测是否存在这个参数。
定义和作用范围:用于测试一个变量是否具有值(包括0,FALSE,或者一个空字串,但不能是NULL),即:“http://localhost/?fo=”也是可以通过检测,因此不适用。但如果是“http://localhost/”参数中并不含fo参数,就可以用isset来检测,此时isset($_GET['fo'])返回false。
不适用于:该函数不适合于验证html表单中的文本的有效方式。要检查用户输入文本是否有效,可以用empty();
empty();——最好用的一个函数。
定义和作用范围:用于检查变量是否具有空值:包括:空字串,0,null 或false,即:“http://localhost/?fo=”或“http://localhost/?fo=0”时,empty检测出来的结果都是ture,不适用范围:不适用于检测可为0的参数。
is_numeric();——只适用于检测数字,但假如参数名不存在,会出错,因此不适合于第一层检测。
综合示例:
代码如下:
ini_set("display_errors",1);
//ini_set("error_reporting",E_ALL); print_r
error_reporting(E_ALL);
$a=NULL;
if(isset($a))echo '变量$a的isset为真';
echo '
isset的情形:
';if(isset($_GET['fo'])){
echo '变量\'fo\'的isset为真,变量可用';
}else{
echo '变量\'fo\'的isset为假,无变量设置';
}
echo '
empty的情形:
';if(empty($_GET['fo'])){
echo '变量\'fo\'的empty为真,即空值或无效值';
}else{
echo '变量\'fo\'的empty为假,有值';
}
echo '
is_numeric的情形:
';if(is_numeric($_GET['fo'])){ //在参数中无fo参数时,则出错。
echo '变量\'fo\'的is_numeric为真,是数字';
}else{
echo '变量\'fo\'的is_numeric为假,不是数字';
}
echo "
\$_GET['fo']=''的情形:
";if($_GET['fo']==''){ //在参数中无fo参数时,则出错。
echo 'fo无值,空的字符串';
}elseif($_GET['fo']!=''){
echo 'fo有值,不为\'\'.';
}
echo "
\$_GET['sex']='m'的情形:
";if($_GET['sex']=='m'){ //当参数中无sex变量时就会出错。
echo '男的';
}elseif($_GET['sex']=='f'){
echo '女的';
}
?>
代码如下:

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