PHP优先级函数声明

Question

I have a question on the way that functions are declared in PHP.

First test :

File "functions.php" => functions toto(){ return "1"; }

Main File

    include("functions.php")
    functions toto(){ return "main"; }
    echo toto();

Second test

File "functions.php" => functions toto(){ return "1"; }

File "functions2.php" => functions toto(){ return "2"; }

Main File

    include("functions.php")
    include("functions2.php")
    echo toto();

Results

The first test work and echo "main"
The second test doesn't work => fatal error "function toto already define"
I make complementary tests :

• in first test : put the functions toto() before include doesn't change the result.
• Create twice functions toto() in the main file create Fatal Error

Someone can explain me how exactly this work ?
Thanks for reading

Answer 1

The PHP statements from the include family do not copy-paste the content of the included file in the context of the includer. The inclusion happens at runtime.

In your first example, the function toto() defined in the main file is created during the compilation. Then, on the execution, the functions.php file is read and parsed. It generates an error because it attempts to define the function toto() that is already defined.

The same happens in the second example during the inclusion of functions.php. Also, you get the same error if you declare the function toto() two times in the main script.

Either way, the PHP functions and constants cannot be re-declared. A quick quote from the documentation:

PHP does not support function overloading, nor is it possible to undefine or redefine previously-declared functions.

You can check if a function is already defined (to avoid defining it again) by using the function_exists() PHP function:

function toto() { return 1; }

if (! function_exists('toto')) {
    function toto() { return 2; }
}