'extern' construction and undefined reference

? Offline

Hi all,

I have been trying to use this "extern" variable for my project, but could not figure out the exact way of doing it. Here is what I have done,

I have a "login" form where I want to assign QString value to a "global_variable". And then use this saved value in a second form "account".

Code I wrote is,

@//login.h
extern QString global_variable //throws error that, storage space assigned

//login.cpp, in a signal slot function
QString global_variable = ui->lineEdit->text();

//account.cpp
#include "login.h"

QString exe = staff_username; // written under function
//: account::account(QWidget *parent) :
//QMainWindow(parent),
//ui(new Ui::staff)

ui->label_name->setText(exe); @

Can anybody help me with this please?

? Offline

Hi all,

I have been trying to use this "extern" variable for my project, but could not figure out the exact way of doing it. Here is what I have done,

I have a "login" form where I want to assign QString value to a "global_variable". And then use this saved value in a second form "account".

Code I wrote is,

@//login.h
extern QString global_variable //throws error that, storage space assigned

//login.cpp, in a signal slot function
QString global_variable = ui->lineEdit->text();

//account.cpp
#include "login.h"

QString exe = staff_username; // written under function
//: account::account(QWidget *parent) :
//QMainWindow(parent),
//ui(new Ui::staff)

ui->label_name->setText(exe); @

Can anybody help me with this please?

andreyc

If this construction is inside a function then it is not global variable.
@
//login.cpp, in a signal slot function
QString global_variable = ui->lineEdit->text();
@

"Global variable":http://www.learncpp.com/cpp-tutorial/42-global-variables/ are declared outside of any functions.

andreyc

If this construction is inside a function then it is not global variable.
@
//login.cpp, in a signal slot function
QString global_variable = ui->lineEdit->text();
@

"Global variable":http://www.learncpp.com/cpp-tutorial/42-global-variables/ are declared outside of any functions.

? Offline

Oh, yes. You were right.
But in my case I need to assign a value in a signal slot function.
How would you suggest me to go on this?

? Offline

Oh, yes. You were right.
But in my case I need to assign a value in a signal slot function.
How would you suggest me to go on this?

andreyc

You need to declare QString global_variable outside of slot function in login.cpp and assign it inside the function.
login.cpp
@
...
QString global_variable;

void slot_function()
{
global_variable = "whatever";
}
@

PS: Using global variables is not good practice.
I would suggest to rethink a design and use class member variables or pass it through signal/slot.

andreyc

You need to declare QString global_variable outside of slot function in login.cpp and assign it inside the function.
login.cpp
@
...
QString global_variable;

void slot_function()
{
global_variable = "whatever";
}
@

PS: Using global variables is not good practice.
I would suggest to rethink a design and use class member variables or pass it through signal/slot.

? Offline

Thanks a lot!!
I was stuck in this since hours.

It is working now..God bless!!

? Offline

Thanks a lot!!
I was stuck in this since hours.

It is working now..God bless!!