function declared globally in main() is not in scope of qt widget slot

Question

I have a qt widget GUI with a button that signals a slot in the QMainWindow. This slot calls a function that is defined in the header of main(), but seems to be undefined once its called from the slot.

Roughly, the problem like this:

#include <required libraries like stdio.h>
#include "window.h"

void testfunc() {printf("I really want to print this");}

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}

My MainWindow object's constructor looks basically like

#include "mainwindow.h"
#include "ui_mainwindow.h"

MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
}

MainWindow::~MainWindow()
{
    delete ui;
}

void MainWindow::on_radioButton_pressed()
{
    testfunc(); //Error: Not in this scope.
}

I'm not sure why the problem occurs. I have tried unsuccessfully changing the order of the #includes in main() to

#include <stdio.h>
void testfunc() {printf("I really want to print this");}
#include "window.h"

Perhaps the problem occurs because the QApplication 'a' that is called by 'a.exec()' that handles QMainWindow's slot does not have testfunc() in its scope?

Another odd thing is some libraries that I have #included already in main() must be re-included in mainwindow.h to be referenced.

There is also some "Dynamic linking" occuring in one of the libraries in main, i'm not sure if this is causing problems.

What is going on?

How do I extend the scope of the function to the slot?

---

edit: Ok, I have a "library.h" I #include and use in "main.cpp". This library has classes and function definitions that are used the the definition a class in "window.h" and its member functions in "window.cpp", and an object of this class is constructed in main().

Do I have to #include "library.h" on the top of window.cpp and/or window.h?

Answer 1

How does the file that has void MainWindow::on_radioButton_pressed() know what testfunc() is if you don't include it? Some way you need to include testfunc() in that file. One way is to move testfunc() into its own header and included it where its needed.

Answer 2

You need to know the difference between define and declare a function. Read this first:

http://www.cprogramming.com/declare_vs_define.html

so you need to declare the function in a header file, call it myglobalvars.h. Include myglobalvars.h ,with the declaration in the main.cpp and in the window.h. and define it in the main.cpp.

At compile time the main has the declaration and the definition of the function, the window has only the declaration, but at link time the implementation of the function is found in the main, so the window can call it from there!

Have fun!