[Solved] Using C++ class in projects

pascal95abc

Hello,

I created a c++ class which I want to use in my projects.
Then I added the path to my pro file with INCLUDEPATH += "../_useful/" and now I want to use those functions.
In my directory specified with includepath, there is the cpp, the header and a file with no extension which contains the code to include the header file so that I can include the class more easily.
Now, I tried
@#include <Useful>@ but I want namespace too!
So how to do so ??
@using namespace Useful;@ didnt work with the errors:
\qtsdk\projects\projekte\eigene\SyncIt\mainwindow.cpp:14: error:'Useful' is not a namespace-name

Thank you for helping me

mlong

Are you wrapping your class definition properly with the namespace?

.h:
@
namespace Useful {

class Foo {
Foo();
...
};

}
@

.cpp:
@
namespace Useful {

Foo::Foo() { ... };

}
@

pascal95abc

No, I don't use namespaces either in my header file or in my cpp file.
I want to make it as easy as it can be done.
So, this is the content of my Useful file:
#include "useful.h"

This is my header:
@#ifndef USEFUL_H
#define USEFUL_H

#include <QWidget>

class Useful : public QWidget
{
Q_OBJECT
public:
explicit Useful(QWidget *parent = 0);
double sqr(double x);

signals:

public slots:
};

#endif // USEFUL_H@

and my cpp
@#include "useful.h"

Useful::Useful(QWidget *parent) :
QWidget(parent)
{
}

double sqr(double x)
{
return(x * x);
}@

So, I just have the sqr function to simplify this thread.

I want to use sqr(4) instead of Useful.sqr(4) in my main/mainwindow cpp.

lycis

As you are wrapping your function inside a class you'll need to call it by using that class. If you only want your function to be inside the namespace you don't need a class, but only wrap this function inside the namespace.

useful.h:
@
namespace useful{
double sqr(double x)
}
@

useful.cpp:
@
double useful::sqr(double x)
{
return (x*x);
}
@

In your main code you may now use either

@
using namespace useful;
...
double foo = sqr(2.0);
...
@

or

@
...
double foo = useful::sqr(2.0);
...
@

If you wrap your function inside a class that's inside a namespace it works the same regarding the namespace usage, but you'll have to instantiate a class for calling the function or declare the function to be static.

pascal95abc

Thanks for the fast answer!

Do I have to set the namespace's name to "useful", i.e. lowercase ?
or should this be
@namespace Useful { ...@
?

And does the whole class useful (class Useful : public QWidget) in the header file be wrapped with "namespace ..." or what do I actually have to wrap with the namespace?

lycis

It does not matter if your namespace is lower or upper case. I wrote it in lower case because I prefer coding conventions where upper case is only applied to classes and namespaces are lower case so you'll if you are using a static class function or a namespace function.

If you are encapsulating your function inside a class (called Useful) that's inside a namespace you'll have to do something like:

@
using namespace MyNamespace;

// if the function is not static
Useful u;
double d = u.sqrt(2.0);

// if the function is static
double d = Useful::sqrt(2.0);
@

If you're not using namespace :

@
// function is non-static
MyNamespace::Useful u;
double d = u.sqrt(2.0);

// function is static
double d = MyNamespace::Useful::sqrt(2.0);
@

pascal95abc

Actually, I want to use namespace to avoid using these long codes to call a simple function like my sqr one.
Is there nothing simple so that I can easily call my function with
@sqr(1.234);@ ?

And you can refer to my code posted "here":http://qt-project.org/forums/viewreply/83941/.

btw: I think line 8 should be
@double d = Useful::sqr(2.0);@ ?

lycis

In that case you should not wrap your function inside a class, but only wrap it inside the namespace. In that case refer to my first post for the definitions. You just need to define the function, but not in a class :)

pascal95abc

Ok, but what to write in the corresponding files in addition ?
The code as is provided by you is clear but not sufficient to be placed in a file.
Sorry, I have no idea what to add.

lycis

Wel, let me give a tested example coding :)

useful.h:
@
#ifndef USEFUL_H
#define USEFUL_H

namespace useful{
double power(double d);
}

#endif // USEFUL_H

@

useful.cpp:
@
#include "useful.h"

double useful::power(double d)
{
return (d*d);
}
@

main.cpp:
@
#include "useful.h"
#include <iostream>

using namespace useful;

int main(int argc, char *argv[])
{
std::cout << "power: " << power(2.0) << std::endl;
return 0;
}
@

This code uses the namespace useful that is defined in useful.h to call the function useful::power(double d) and prints the result to the default output.

Hope this helps you somewhat more.

pascal95abc

Thank you, this is great.
It was exactly what I was looking for. Now I will extend this code with really useful functions and some structs I want to access to from other projects easily ;)