如何判断变量为空,话不多说,直接代码
$testisset ="赋值了"; $results = array(); array_push($results,["state"=>"变量被赋值","testfun"=>"isset()","result"=>isset($testisset),"resultdes"=>"isset返回true"]); array_push($results,["state"=>"变量被赋值","testfun"=>"empty()","result"=>empty($testisset),"resultdes"=>"empty返回false"]); array_push($results,["state"=>"变量被赋值","testfun"=>"is_null()","result"=>is_null($testisset),"resultdes"=>"is_null返回false"]); array_push($results,["state"=>"变量被赋值","testfun"=>"var == null","result"=>$testisset==null,"resultdes"=>"var == null返回false"]); array_push($results,["state"=>"变量被赋值","testfun"=>"var === null","result"=>$testisset===null,"resultdes"=>"var === null返回false"]); unset($testisset); array_push($results,["state"=>"变量unset后","testfun"=>"isset()","result"=>isset($testisset),"resultdes"=>"isset返回false"]); array_push($results,["state"=>"变量unset后","testfun"=>"empty()","result"=>empty($testisset),"resultdes"=>"empty返回true"]); array_push($results,["state"=>"变量unset后","testfun"=>"is_null()","result"=>"","resultdes"=>"函数调用时报错"]); array_push($results,["state"=>"变量unset后","testfun"=>"var == null","result"=>"","resultdes"=>"函数调用时报错"]); array_push($results,["state"=>"变量unset后","testfun"=>"var === null","result"=>"","resultdes"=>"函数调用时报错"]); $testisset = null; array_push($results,["state"=>"变量被设置为null","testfun"=>"isset()","result"=>isset($testisset),"resultdes"=>"isset返回false"]); array_push($results,["state"=>"变量被设置为null","testfun"=>"empty()","result"=>empty($testisset),"resultdes"=>"empty返回true"]); array_push($results,["state"=>"变量被设置为null","testfun"=>"is_null()","result"=>is_null($testisset),"resultdes"=>"is_null返回true"]); array_push($results,["state"=>"变量被设置为null","testfun"=>"var == null","result"=>$testisset==null,"resultdes"=>"var == null返回true"]); array_push($results,["state"=>"变量被设置为null","testfun"=>"var === null","result"=>$testisset===null,"resultdes"=>"var === null返回true"]); $testisset = 0; array_push($results,["state"=>"变量被设置为数字0","testfun"=>"isset()","result"=>isset($testisset),"resultdes"=>"isset返回true"]); array_push($results,["state"=>"变量被设置为数字0","testfun"=>"empty()","result"=>empty($testisset),"resultdes"=>"empty返回true"]); array_push($results,["state"=>"变量被设置为数字0","testfun"=>"is_null()","result"=>is_null($testisset),"resultdes"=>"is_null返回false"]); array_push($results,["state"=>"变量被设置为数字0","testfun"=>"var == null","result"=>$testisset==null,"resultdes"=>"var == null返回true"]); array_push($results,["state"=>"变量被设置为数字0","testfun"=>"var === null","result"=>$testisset===null,"resultdes"=>"var === null返回false"]); $testisset = "0"; array_push($results,["state"=>"变量被设置为字符串0","testfun"=>"isset()","result"=>isset($testisset),"resultdes"=>"isset返回true"]); array_push($results,["state"=>"变量被设置为字符串0","testfun"=>"empty()","result"=>empty($testisset),"resultdes"=>"empty返回true"]); array_push($results,["state"=>"变量被设置为字符串0","testfun"=>"is_null()","result"=>is_null($testisset),"resultdes"=>"is_null返回false"]); array_push($results,["state"=>"变量被设置为字符串0","testfun"=>"var == null","result"=>$testisset==null,"resultdes"=>"var == null返回false"]); array_push($results,["state"=>"变量被设置为字符串0","testfun"=>"var === null","result"=>$testisset===null,"resultdes"=>"var === null返回false"]); $testisset = false; array_push($results,["state"=>"变量被设置为false","testfun"=>"isset()","result"=>isset($testisset),"resultdes"=>"isset返回true"]); array_push($results,["state"=>"变量被设置为false","testfun"=>"empty()","result"=>empty($testisset),"resultdes"=>"empty返回true"]); array_push($results,["state"=>"变量被设置为false","testfun"=>"is_null()","result"=>is_null($testisset),"resultdes"=>"is_null返回false"]); array_push($results,["state"=>"变量被设置为false","testfun"=>"var == null","result"=>$testisset==null,"resultdes"=>"var == null返回true"]); array_push($results,["state"=>"变量被设置为false","testfun"=>"var === null","result"=>$testisset===null,"resultdes"=>"var === null返回false"]); $testisset = ""; array_push($results,["state"=>"变量被设置为空字符串","testfun"=>"isset()","result"=>isset($testisset),"resultdes"=>"isset返回true"]); array_push($results,["state"=>"变量被设置为空字符串","testfun"=>"empty()","result"=>empty($testisset),"resultdes"=>"empty返回true"]); array_push($results,["state"=>"变量被设置为空字符串","testfun"=>"is_null()","result"=>is_null($testisset),"resultdes"=>"is_null返回false"]); array_push($results,["state"=>"变量被设置为空字符串","testfun"=>"var == null","result"=>$testisset==null,"resultdes"=>"var == null返回true"]); array_push($results,["state"=>"变量被设置为空字符串","testfun"=>"var === null","result"=>$testisset===null,"resultdes"=>"var === null返回false"]);
结果如下:
结论:
//isset对于未初始化或者为null的变量返回false,表明未被初始化
//empty对于未被初始化,为null,数字0,字符串0,false,空字符串,都会返回true,表示变量是空的,所以empty就是将变量强转为boolean类型,然后返回
//is_null当变量为null时会返回true
//var == null当变量为null,数字0,false,空字符串时都会返回true
//var === null当变量为null是才会返回true
php中boolean类型详解
当转换为 boolean 时，以下值被认为是 false;
boolean(false);
int(0)
float(0.0)
空字符串及字符串0
不包括任何元素的数组
特殊类型 null (包括尚未设定的变量)
当转换为 boolean 时，以下值被认为是 false;
布尔转字符串时，true=>1，false=>;
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以上就是php中boolean的判定详解的详细内容。