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up vote 4 down vote favorite

This is a solution for a problem that I had and could not find an answer for anywhere. It involves Global Variable Scope and multiple functions.

Basically, I wanted one function to declare variables and then have a second nested function use those variables. This works fine when a script declares the variables and then calls a function that uses those variables after declaring global $var1, $var2;.

However, I had problems with the nested function seeing variables that the parent function declared, using the same code logic as for a script calling a function.

The solution was to write:

function function_1(){
  global $var1, $var2;
  $var1=0;
  $var2=0;
  function function_2(){
     global $var1, $var2;
  }
  function_2();//call to nested function.
}

All variables interact properly in this case.

If you state 'global' after you declare the variables in function_1, you simply wipe out the value of the variables (you declare new variables with no values?).

Hope this helps someone :)

Greg

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can u post the code ? –  xsari3x Aug 20 '11 at 20:44
    
The thing is that the inner function ends up in the global scope. In PHP you can achieve what you wanted using an anonymous (inner) function or a class. –  Ionuț G. Stan Aug 20 '11 at 20:45
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3 Answers

up vote 1 down vote

Don't use global variables. Use use ($var1,$var2) so you do not need to globalize your variables

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up vote 0 down vote

You should use closure: function function_2 use ($var1, $var2)() { }

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up vote 0 down vote

To illustrate what genesis was saying, do the following:

function func1($a, $b) // <-- function DEFINITION for func1
{
    // do stuff wit $a and $b

    func2($a, $b); // <-- function INVOCATION of func2 within func1
}

func2($y, $z) // <-- function DEFINITION for func2
{
    // do stuff with $y and $z
}

// --------------------------------

$param1 = "some value";
$param2 = "some other value";

func1($param1, $param2); // <-- explicit INVOCATION of func1... func2 is also invoked within

Never use the 'global' keyword to pass parameters into a function. Functions have argument lists for a reason.

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I will revisit the idea of closure. I first tried this using parameters, but it was not working for me. Function 2 was updating variables that Function 1 was using in its call to Function 2. I needed to get the value of the updated variables out of Function 2 without using 'return'. –  Greg Aug 20 '11 at 21:43
1  
Have you tried passing them into Function 2 by reference? The default mechanism in PHP for variables being passed into a function is by value. This means that a COPY of the variable is made, and passed into the function. That's why a value needs to be returned if you want changes to be retained - the copy is what's changed, and if it's not returned, it will be destroyed as the function ends and everything in its scope is destroyed. –  KevinM1 Aug 20 '11 at 21:48
1  
Pass by reference means you pass a reference of the variables into the function. Whatever changes you make to the variables inside the function will be retained outside of the function, thereby eliminating your need to return the new values at all. –  KevinM1 Aug 20 '11 at 21:50
    
See: php.net/manual/en/language.references.pass.php –  KevinM1 Aug 20 '11 at 21:51
1  
Functions are supposed to have a clear signature - their name, what arguments are required to get them to work, and what kind of value(s) will be returned. 'Global' adds an implicit requirement to the function, and ties it to a particular scope. For the function to work, the global value MUST be present in the global scope. Good luck trying to develop a clean, modular system with hidden caveats buried into your functions. It may not seem like a big deal if you're the only one working on the system, but it's a nightmare down the road. –  KevinM1 Aug 20 '11 at 22:01
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