[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.