PHP function in function (no OOP) works weird

Question

I'm not in OOP and I would like understand why in the procedural mode I can declare a function nestled in a function without errors, but I can call the nestled function from the "main" and cannot call from the primary function?

Example 1: calling b() in a() gives Fatal error / Why a() doesn't views b() ?

<?php
function a(){
  // do something
  b(); //Fatal error: Call to undefined function b()

  function b(){
    // do something
  }
}

a();

Example 2: calling b() from the main gives Fatal error (this is logic)

<?php
function a(){
  //  do something

  function b(){
    // do something
  }
} 

b(); // Fatal error: Call to undefined function b()

Example 3: calling a() and then calling b() from the main doesn't give error

<?php
function a(){
    //  do something

    function b(){
        // do something
    }

}

a();
b();

Just follow the flow of the script, the function is still undefined when you try to call it in #1 and #2. By the way, this is bound to give you trouble later on as you can only call a() once during the whole execution of your script. — jeroen
– jeroen, Commented Mar 27, 2018 at 13:29
Nesting functions in PHP is rarely what you want to do - it means that b() is only declared once you first call a(), and will raise an error about redeclaring an existing function if you ever call a() again. Both functions will be declared in global scope, which isn't necessarily obvious. — iainn
– iainn, Commented Mar 27, 2018 at 13:32
@iainn surely, but suppose I need to use the function b() only in the function a() ... probably it shall be better use a LAMBDA function I suppose — ViDiVe
– ViDiVe, Commented Mar 27, 2018 at 13:40
@ViDiVe Yes, you should absolutely use a locally scoped anonymous function in that case. Having the functions nested as you have will cause issues with both scope and re-usability. — iainn
– iainn, Commented Mar 27, 2018 at 13:52

Richard Parnaby-King · Accepted Answer · 2018-03-27 13:31:53Z

3

PHP is a procedural programming language. It will do each line, in order. The reason you can't call b() from within a() is because, at that point, b() has not been declared. What you want to do is declare your function before calling it:

<?php
function a(){
  // do something

  function b(){
    // do something
  }
  b(); 

}

a();

This is still bad practice though. Break b() out of a() :

<?php
function a(){
  // do something

  b();

}
function b(){
  // do something
}

a();

This will allow you to call a() and b() at any time.

answered Mar 27, 2018 at 13:31

Richard Parnaby-King

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1 Comment

ViDiVe Over a year ago

Thanks, now I've understood!

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