C++ Initializing a static member variable by passing it as a parameter?

Question

I have a static member variable ,I want to initialize it by passing it to a function which modifies its own parameter ,like:

Class MyClass
{
 static RECT rcRect;//The RECT structure defines the coordinates of the upper-left and lower-right corners of a rectangle.
}

GetClientRect(GetDesktopWindow(),&rcRect);
//Windows API,
//GetDesktopWindow retrieves a handle to the desktop window ,
//GetClientRect gets the coordinates of the desktop's client area ,
//and passes it to rcRECT

The only way I can think of is to initialize it in the main function . My question is :Is this the only way to do it? How Can I initialize it in the .h file ?

Answer 1

Your function will only modify a copy of p that goes out of scope as soon the function returns.

To modify any variable passed in used a reference parameter:

 void func(Typename& p)
                // ^

---

Static class members can be initialized in the class declaration using constexpr :

 class Foo {
     static constexpr Typename func();
     static constexpr Typename bar = func(); 
 };

See here also please.

Answer 2

you can modify it in the .h file by :

#ifndef FILENAME_H
#define FILENAME_H

you can also include any header you needed here like stdio or stdlib if you want then write the procedure / function

void func(Typename& p);

After that you must create a .cpp file to implement this header (because in header file you only write the procedure / function not the implementation)

#include "filename.h"

void func(Typename& p)
{
//code here,
//modifies the value of p
};

Finally in your driver (main program you can use it by include the .h file)