[Solved] Operator<< Overloading for std::cout, does not work.

[Galiego710]

I have simple console project in Qt, where I am overloading << operator.
The next files:

• Overload_operation.pro
• main.cpp
• MyClass.cpp
• MyClass.h

Contents:
Overload_operation.pro
@QT += core
QT -= gui

TARGET = Overload_operation
CONFIG += console
CONFIG -= app_bundle

TEMPLATE = app

SOURCES += main.cpp
MyClass.cpp

HEADERS +=
MyClass.h
@
main.cpp
@#include <QtCore/QCoreApplication>
#include <iostream>
#include "MyClass.h"

using namespace std;

int main(int argc, char *argv[])
{
cout << "Test" << endl;
return 0;
}@
MyClass.h
@#ifndef MYCLASS_H
#define MYCLASS_H

#include "iostream"
using namespace std; ///< Using std

/// My simple Class
class MyClass
{
private:
int m_val; ///< value
public:
MyClass();

void setVal(int val);   ///< set value
int val();              ///< get value

/// Set the friend function
friend ostream& operator<<(ostream& cout_, const MyClass& obj_);

};

/// overloading operator<<
ostream& operator<<(ostream& currCout, const MyClass& currObj)
{
currCout << currObj.m_val;
return currCout;
}

#endif // MYCLASS_H@
MyClass.cpp
@#include "MyClass.h"
#include "iostream"

MyClass::MyClass()
{
m_val = 0;
}

void MyClass::setVal(int val)
{
m_val = val;
}

int MyClass::val()
{
return m_val;
}@

But I get the next errors:
@
D:\Projects_Qt\MyExamples\Overload_operation-build-desktop-Qt_4_7_4_for_Desktop_-_MinGW_4_4__Qt_SDK__Debug\debug\MyClass.o:-1: In function `ZlsRSoRK7MyClass':

D:\Projects_Qt\MyExamples\Overload_operation-build-desktop-Qt_4_7_4_for_Desktop_-_MinGW_4_4__Qt_SDK__Debug..\Overload_operation\MyClass.h:24: multiple definition of `operator<<(std::ostream&, MyClass const&)'

D:\Projects_Qt\MyExamples\Overload_operation-build-desktop-Qt_4_7_4_for_Desktop_-_MinGW_4_4__Qt_SDK__Debug..\Overload_operation\MyClass.h:24: error: first defined here

:-1: error: collect2: ld returned 1 exit status
@

Here is written that "multiple definition of `operator<<(std::ostream&, MyClass const&)'", but when was it?
How I can make it correct?

Thanks.

——————
Best regards,
Galiego710

[giesbert]

The problem is, that you implement the function in the header file, which implies, it is implemented in each include. Implement it inthe cpp file and it is fine.

[Galiego710]

I put it
@/// overloading operator<<
ostream& operator<<(ostream& currCout, const MyClass& currObj)
{
currCout << currObj.m_val;
return currCout;
}@
in any cpp file. It's work!
Strangely, before I did about the same, but did not work.

I found a few useful links for operator<< qDebug() in Qt doc
http://doc.trolltech.com/4.6/debug.html#providing-support-for-the-qdebug-stream-operator
http://doc.trolltech.com/4.6/custom-types.html

Thank you very much!

[goetz]

It works in the header file if you have an operator definition inside a class declaration.