在PHP中定义一个全局变量

Question

I want to use a variable outside my foreach. how can I solve that in PHP. How can I use $ID outside the foreach?

foreach($row as $key => $value) {
  $ID = $value['Id'];
}

Answer 1

Your $ID variable can already be used outside of your foreach : a control structure doesn't come with its own variable scope .

As a quick illustration, the following portion of code :

$ID = 0;

$array = array(1, 2, 3);
foreach ($array as $value) {
    $ID = $value;
}

var_dump($ID);

Will get you :

int 3

Which shows that the $I D variable that's used inside the foreach loop is the same as the one that exists outside that loop.

---

Edit after the comments :

Not initializing the variable before the loop, you'd get exactly the same result : the variable would be created the first time it used -- and it would in the same scope as in the example I posted.

Another example, now, using a function inside the foreach loop (only works with PHP >= 5.3) :

$array = array(1, 2, 3);
foreach ($array as $value) {
    $func = function () use ($value) {
        $ID = $value;
        var_dump($ID);
    };
    $func();
}

var_dump($ID);

There, the $ID variable is not initialized before the loop -- it's created in the function that's inside the loop.

This example would get the following output :

int 1
int 2
int 3

( ! ) Notice: Undefined variable: ID ... on line 15

null

Basically :

• You get three correct output, from inside the function
  • Those show the $ID variable, inside the anonymous function, is getting a value
• But, after the loop, you get a notice : the $ID variable doesn't exist.
  • Which show that the $ID variable created inside the function is not the same as the $ID variable outside the function : the function comes with its own variable scope.

Answer 2

You can use it outside your foreach , variables scopes are not limited by statement structure.

On the other hand, they are limited by functions scope.

See this page from the manual http://php.net/manual/en/language.variables.scope.php for more informations about variables scope.

Answer 3

$ID = null;
foreach($row as $key => $value) {
  $ID = $value['Id'];
}
//do something with $ID...

The reason for this is that if the for loop is never gone through (that is, $row was an empty array) $ID would never be set. Therefore, $ID has to be set beforehand or else it won't be in scope at all and if you try to access $ID 's value, you will hit errors.

Answer 4

Having a variable inside a foreach loop does affect it's scope. You are free to manipulate that variable before, after or in the foreach loop to your desires.

Answer 5

there is not much sense in assigning all values to single variable in turn.
if you want only last one, it can be substituted with

$value = array_pop($row);
$ID = $value['Id'];

but I doubt it's what you really need. what is whole task you're trying to solve? May be you want an array?

$id_arr = array();
foreach($row as $key => $value) {
  $id_arr[] = $value['Id'];
}