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Old 02-12-2009, 10:59 AM   #1
Registered: Apr 2008
Location: Espaņa
Distribution: Suse
Posts: 220

Rep: Reputation: 32
Problem when link my program.....


I have a QT programm and now I use a function in C code.
When I try to compile, I have the follow error:
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o forminit.o forminit.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o main.o main.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o mydialog.o mydialog.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o form2.o form2.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o form3.o form3.cpp
gcc -c -pipe -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o taskman.o taskman.c
/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/bin/moc forminit.h -o moc_forminit.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o moc_forminit.o moc_forminit.cpp
/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/bin/moc mydialog.h -o moc_mydialog.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o moc_mydialog.o moc_mydialog.cpp
/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/bin/moc form2.h -o moc_form2.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o moc_form2.o moc_form2.cpp
/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/bin/moc form3.h -o moc_form3.cpp
g++ -c -pipe -DQWS -fno-exceptions -fno-rtti -m32 -mtune=geode -O2 -DQT_NO_DEBUG -DQT_SHARED -I/usr/include -I. -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/mkspecs/default -I/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/include -o moc_form3.o moc_form3.cpp
g++ -m32 -mtune=geode -Wl,-rpath,/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/lib -o prueba_ui forminit.o main.o mydialog.o form2.o form3.o taskman.o moc_forminit.o moc_mydialog.o moc_form2.o moc_form3.o -L/home/john/GeodeProject/Qt-embedded/qt-embedded-free-3.3.6/lib -L/home/john/GeodeProject/Qt-embedded/tslib-src/compilado/lib -lqte -ldl -lrt -lpthread -lts -lpcican
main.o: In function `main':
main.cpp.text+0x41): undefined reference to `init_rt_function()'
collect2: ld returned 1 exit status
make: *** [prueba_ui] Error 1

In main.cpp there is the follow code:

#include <qapplication.h>
//#include "forminit.h"
#include "mydialog.h"
#include <qwidget.h>
#include <qnamespace.h>
#include "taskman.h"

int main( int argc, char ** argv )
unsigned int valor;

QApplication a( argc, argv );
//FormInit w;
MyDialog w;
valor = init_rt_function(); ---> MY PROBLEM;
w.setWindowState( 0x00000004 );
a.connect( &a, SIGNAL( lastWindowClosed() ), &a, SLOT( quit() ) );
return a.exec();
And I have declared the prototype in taskman.h
#ifndef _TASKMAN_H
#define _TASKMAN_H

int init_rt_function(void);

#endif /* _TASKMAN_H */
And in taskman.c there is the code of function:

int init_rt_function(void)
signum = SIGALRM;


return 0;

I have looked for information about it, but I can not fix this problem.

Thanks a lot
Old 02-12-2009, 07:24 PM   #2
Registered: Jan 2009
Posts: 100

Rep: Reputation: 17
Is taskman.c part of your QT Make file?
QT has it's own ways of building applications and my first guess is that you have not updated your .pro file and are still using the old Makefile (QT creates Makefiles based on .pro file).


Last edited by servat78; 02-19-2009 at 12:21 PM.
Old 02-13-2009, 03:25 AM   #3
Registered: Apr 2008
Location: Espaņa
Distribution: Suse
Posts: 220

Original Poster
Rep: Reputation: 32
Yes, I have updated my Makefile with the new file.

But I have found my problem, in taskman.h I have changed the code with this:

#ifndef _TASKMAN_H
#define _TASKMAN_H

#ifdef __cplusplus ----> What does mean???
extern "C" {

int init_rt_function(void);

#ifdef __cplusplus

#endif /* _TASKMAN_H */
I never have programmed in C++, and I do not known what does mean the new code.

Best regards
Old 02-13-2009, 03:30 AM   #4
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Registered: Dec 2007
Location: Croatia
Distribution: Debian GNU/Linux
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Here's a very nice explanation;
C++ supports certain powerful but complex features that mean that
different functions and variables can have different names:
specifically, in C++ function names can be overloaded (two functions can
have the same name, but different argument signatures), and also C++
supports "namespaces", which granulate visibility in C's single global
external namespace.

To get around these problems, C++ compilers commonly "mangle" function
names: that is, the function name that appears in the global namespace
will be a string obtained in some way or other from the actual name of
the function as it appears in the code, the type and number of its
arguments, and any namespace qualifications needed to specify it.

This means that if a C++ program tries to use functions from a C
library, then there will be problems: when the C++ linker sees a
function called foobar, it will actually look in the symbol table for
something like foorbar__Fii.

To get around this, there's a way for the programmer to tell his
C++ linker that some of the functions have "C linkage", and so it
shouldn't try to mangle their names. This is achived by surrounding the
code with
extern "C" {

Sometimes, people write functions in C and then want to create a single
header that will let people use their functions either in C or C++.

To accomplish this, they make use of the fact that the macro __cplusplus
will be defined by the compiler if and only if it's compiling the
program as C++, and include the extern "C" lines conditional on the
presence of this macro. Therefore, if the file is being compiled as C
then this little bit of C++ will vanish during preprocessing, and won't
choke the C compiler.
Old 02-13-2009, 04:33 AM   #5
Registered: Apr 2008
Location: Espaņa
Distribution: Suse
Posts: 220

Original Poster
Rep: Reputation: 32
hello alan_ri,

Good explanation.

Thanks a lot.


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