Calling a function before it's defined | PHP

问题

Is there any possible way when in one file - please note, just one file. To call a function when it isn't defined yet, e.g.

<?php

echo global_title();

function global_title()
{
    $title = $_GET['name'];

    return $title;
}

?>

I don't know how to explain this, but it's not quite possible isn't it? What about variable from another file (without including it) can be called in a different file, e.g.

config.php

<?php

$db = "localhost";

?>

index.php

<?php

// I do not want it to be accessed by including it or using sessions

echo $db;

?>

Know what I mean? :)

回答1:

You can call a function which is defined after calling it. That's because PHP first parses the file and then executes it.

As for the variable - this is not possible, you have to include the file.

回答2:

I just discovered that you can call a function if it's defined later in the same file.
But if it's defined in an other file, you must include the file before calling the function.

my_func();
function my_func() {...}
--->   No problem

but

my_func();
include_once 'define_my_func.php';
--->   PHP Fatal error

It's like a conditional function as in the example 2 on the doc on user-defined functions

回答3:

You cannot call undefined function, it will raise a fatal error. although in procedural code it can be called and afterwards defined. As the script is first parsed then executed. includes don't matter, they behave as if they were written in the exact file.

there's no such thing as a variable "from a file". if the code defines the variable is not run, it can't be there.

来源：https://stackoverflow.com/questions/3559875/calling-a-function-before-its-defined-php

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