Making global var from inside a function in PHP

问题

I am trying to define dynamically variables. I am using a function for this, but I don't know how to define the new var as global (because it never created before the function).

is that possible ?

Thanks.

edit

ok, this is what I've built. is it that dangerous ?

function extract_values($row) {
    foreach ($row as $key => $value){
        global $$key;
        $$key = $value;
    }
}

and then I'm trying to make my life easier like that:

$result = mysql_query("SELECT first_name, last_name, address FROM users ORDER BY id ASC");

    while ($row = mysql_fetch_array($result)){
        extract_values($row);
#[do some stuff with the variables.]#
}

I am doing it to save time. instead of creating for each column it's own variable like

$first_name = $row['first_name'];

This function does that for me. I don't see why in this case it might be dangerous.. or as usuall, i am missing something..

回答1:

Try this:

function doSomething() {
  global $x;
  $x = 5;
}

If you prefer to save a couple of bytes, you can use the $_GLOBALS array for this:

$_GLOBALS['x'] = 5;

回答2:

Regarding your edit: It makes your code less understandable.

Actually, there already exists a function that is doing this: extract().

while (($row = mysql_fetch_assoc($result))){
    extract($row);
    // ...
}

extract() is even better, because it lets you specify what should happen if the variable already exists and/or lets you specify a prefix (so you don't overwrite already existing variables with that name). E.g. you could do:

extract($row, EXTR_PREFIX_ALL, 'db');

which would result in $db_first_name etc.

Surly, extract() is also doing some internal work here, but using built-in functions is always better than creating your own.

Another possibility would be to use list():

while (($row = mysql_fetch_row($result))){
    list($first_name, $last_name, $address) = $row;
    // ...
}

回答3:

You can do it in two ways:

Make the variable global using the global keyword:

function fun1() {
        global $foo;
        $foo = 1;
}

Alternatively you can also create an new element in the $GLOBALS array:

function fun2() {

        $GLOBALS['bar'] = 1;
}

Working code

Remember that these are considered bad practice, a function should have local variables invisible outside and should get inputs through the arguments passed. You should avoid getting arguments though global variables and must completely avoid crating global variables.

来源：https://stackoverflow.com/questions/3940333/making-global-var-from-inside-a-function-in-php

标签

php

variables

function

global-variables

global