Mixing C and C++/Qt code

[lovebingheji]

@
#ifdef SUM_H //this is sum.h
extern "C"{
#endif

int mySum(int a,int b);

#ifdef SUM_H
}

#endif // SUM_H
@

---

@
#include "sum.h" //this is sum.c

int mySum(int a, int b)
{

return a + b;

}
@

---

@
#include <QtCore/QCoreApplication> // this is main.cpp
#include <QDebug>
#include "sum.h"

int main(int argc, char *argv[])
{

QCoreApplication a(argc, argv);
int i = 5;
int j = 6;
int k;

k = mySum(i,j);
qDebug() << "this sum is " << k;
return a.exec&#40;&#41;;

}
@

---

but it was wrong with /home/lovebingheji/qt/test-build-desktop-Qt_4_6_2_in_PATH__System__Release/../test/main.cpp:13: error: undefined reference to `mySum(int, int)'

but when i was iadd #include "sum.c" in main.cpp that is right

@
#include <QtCore/QCoreApplication>
#include <QDebug>
#include "sum.h"
#include "sum.c"
int main(int argc, char *argv[])
{

QCoreApplication a(argc, argv);
int i = 5;
int j = 6;
int k;

k = mySum(i,j);
qDebug() << "this sum is " << k;
return a.exec(&#41;;

}
@

---

why i just want main.cpp include "sum.h" but "sum.c" how can i should do ?
i create a QT console application project,please help me.thanks very much

[lovebingheji]

my email :lovebingheji@gmail.com please also can answer the question to send my email.

[goetz]

Welcome to the forums. Some housekeeping first:

• wrap code in @-tags or use the editor's button. It makes your code look nicely and adds some pretty printing. I've added them for your, but please format yourself next time
• adding your question to quite old threads (the "original thread":http://qt-project.org/forums/viewthread/10975/ dates back to October last year) isn't that useful, better open a new thread with a decent topic. I've split your question off to a new thread for that reason.
• begging for private answers usually leads you to no answers at all. This is a public forum, with everyone answering in their spare times. We do not do private support. Read http://www.catb.org/~esr/faqs/smart-questions.html for some explanations

Regarding your actual question: The sum.h header file is plain wrong. Use this one

@
#ifndef SUM_H
#define SUM_H

#ifdef __cplusplus
extern "C" {
#endif

int mySum(int a, int b);

#ifdef __cplusplus
}
#endif
#endif // SUM_H
@

And then make sure that your sum.c implementation file is actually added to the list of source files and gets compiled and linked to your application.