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To: "\"Andrew Mather \(BT Std\)\"" <an.dromeda@btconnect.com>
Cc: <internals@lists.php.net>
References: <200603112311.19732.an.dromeda@btconnect.com>
Date: Sat, 11 Mar 2006 22:15:42 -0800
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Subject: Re: Separating C++ zend object creation code from module code
From: pollita@php.net ("Sara Golemon")

> The nuance of cross-referencing these calls between two .cpp files (listed 
> in
> config.m4, and so compiled into distinct .o files), eludes me.
>
> It's a c/cpp grammar issue, I guess, but one I've never had to deal with 
> till
> now.
>
Quick Lesson:

static: Symbols (functions, variables, etc...) declared static are not 
exported.  This means that no other object (source file) has any way of 
knowing where these symbols are located and thus cannot call them.    When a 
symbol is known not to be used outside of a given source file, it's given 
the static modifier to avoid polluting the process' symbol space with 
uneccesary references.  It also avoids namespace collisions for more 
commonly named methods.

extern: Typically used in header files with function prototype declarations. 
It allows one object file to be aware of the prototype and calling semantics 
for a function in another object file.

For example:

header.h

extern foo(void);
extern bar(void);


file1.c

#include "header.h"

void foo(void)
{
    /* do whatever */
}

static void local_func(void)
{
    bar();
}

int main(int argc, char *argv[])
{
  local_func();
}


file2.c

#include "header.h"

void bar(void)
{
  foo();
}

Same idea for .cpp of course...  There are some other things to keep in mind 
when interfacing between C and C++ (calling semantics) or when developing 
DLLs for windows (linkage export semantics), but you're most likely not 
going to have to worry about these as the PHP extension magic pretty much 
covers this for you.

-Sara