isset（）和PHP全局变量

问题描述

 函数hello_testing（）{
 global $ conditional_random; 
 if（isset（$ conditional_random））{
 echofoo is inside; 
 
 
 
 
 $ b 
全局变量（conditional_random）可能未被初始化调用 hello_testing（）函数。
 
 
那么，通过 isset（）何时 $ conditional_random 未初始化？它会失败还是永远是真的？
解决方案
那么，为什么你不测试？ ;  - ）
 
 
 
 注意：不像您想象的那么容易 - 阅读完整答案;  - ）
 
 
 
 
 
调用 hello_testing（）; 函数，不设置变量：
 
 
  hello_testing（）; 
  
我没有输出 - 表示返回  false  
  
 
设置变量后调用该函数： 
 $ b  $ b 
  $ conditional_random ='blah'; 
 hello_testing（）; 
  
我得到一个输出： 
 
 
  foo在
之内 
这表示按预期工作，变量已设置  - 好吧，对此应该没有任何疑问^^  
 
 
 
 
 
 
 
 
 
 
 
 但请注意 isset 会返回 false 如果设置了变量，并且 null ！ 
 
请参阅 
 
 
这意味着更好的测试是：
 
 
 函数hello_testing（）{
全球$ conditional_random; 
 var_dump（$ conditional_random）; 
} 
 
 hello_testing（）; 
  
并显示： 
 
 
  null 
  
否注意：变量存在！即使 null 。
 
 
 
因为我没有在函数外设置变量，所以它显示 global  设置变量 - 但它并没有给它赋值;这意味着它是 null ，如果尚未设置在函数之外。
 
 
 
 
 
 While：
 函数hello_testing（）{
 // global $ conditional_random; 
 var_dump（$ conditional_random）; 
} 
 
 hello_testing（）; 
  
给出： 
 
 
 注意：未定义变量：conditional_random 
  
证明已启用通知;  - ）
 
 
 
而且，如果全局变量不是 set ，则前面的示例会给出相同的通知。
 
 
  
最后： 
 
 
 函数hello_testing（）{
 global $ conditional_random; 
 var_dump（$ conditional_random）; 
} 
 
 $ conditional_random ='glop'; 
 hello_testing（）; 
  
给出： 
 
 
  string'glop'（length = 4）
  
我的例子不被欺骗^^） 
 
I have a question about global variable initialization.
function hello_testing() {
  global $conditional_random;
  if (isset($conditional_random)) {
      echo "foo is inside";
  }
}
The global variable (conditional_random) may not be initialized before the hello_testing() function is called.
So, what happens to my validation via isset() when $conditional_random is not initialized? Will it fail or it will always be true?
 解决方案 
Well, why don't you just test ? ;-)
Note : Not as easy as you'd think -- read the full answer ;-)

Calling the hello_testing(); function, without setting the variable :
hello_testing();
I get no output -- which indicates isset returned false.

Calling the function, after setting the variable :
$conditional_random = 'blah';
hello_testing();
I get an output :
foo is inside
Which indicates global works as expected, when the variable is set -- well, one should not have any doubt about that ^^

BUT note that isset will return false if a variable is set, and null !
See the manual page of isset()
Which means that a better test would be :
function hello_testing() {
  global $conditional_random;
  var_dump($conditional_random);
}

hello_testing();
And this displays :
null
No Notice : the variable exists ! Even if null.
As I didn't set the variable outside of the function, it shows that global sets the variable -- but it doesn't put a value into it ; which means it's null if not already set outside the function.

While :
function hello_testing() {
  //global $conditional_random;
  var_dump($conditional_random);
}

hello_testing();
Gives :
Notice: Undefined variable: conditional_random
Proves that notices are enabled ;-)
And, if global didn't "set" the variable, the previous example would have given the same notice.

And, finally :
function hello_testing() {
  global $conditional_random;
  var_dump($conditional_random);
}

$conditional_random = 'glop';
hello_testing();
Gives :
string 'glop' (length=4)
(Purely to demonstrate my example is not tricked ^^ )
                        
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