I cannot link my project because of some issues with the qjpeg4 library.
Its DLL is located here:
PROJECT_ROOT/../Release/obj/imageformats/qjpeg4.dll
I get this linker error:
Linking CXX executable test.exe
CMakeFiles\test.dir/objects.a(entrypoint.cpp.obj):entrypoint.cpp:(.text.startup+0x2692): undefined reference to `qt_plugin_instance_qjpeg()'
collect2: ld returned 1 exit status
In the file containing main() I have: Q_IMPORT_PLUGIN(qjpeg)
I tried adding these lines, with no improvement:
QApplication app(argc, argv);
QString sDir = QCoreApplication::applicationDirPath();
app.addLibraryPath(sDir + "/plugins");
The previous error should even not depend on the fact that the DLL has not been found, since it is still in the link phase...
If in the file containing main() I remove Q_IMPORT_PLUGIN(qjpeg), the linker is successful, but the executable does absolutely nothing.
The only Qt headers I include are <QApplication> and <QtPlugin>; adding <QtGui> has been useless.
From this link, it seems to be a bug in Qt:
https://bugreports.qt-project.org/browse/QTBUG-24177
Related
I'm using the Mozzi lib (http://sensorium.github.io/Mozzi/) as part of a tutorial (http://www.echanter.com/home/howto-build#TOC-Arduino-IDE). I included the Mozzi in Arduino Studio and followed minor configs in the tutorial. I've looked around the lines that are reported, but I'm stumped. Compile error is:
Mozzi/mozzi_fixmath.cpp.o: In function isqrt16(unsigned int)': /home/temp/sketchbook/libraries/Mozzi/mozzi_fixmath.cpp:156: multiple definition of isqrt32(unsigned long)'
echanter.cpp.o:/home/temp/sketchbook/libraries/Mozzi/Sample.h:61: first defined here
collect2: error: ld returned 1 exit status
In the root dir are two files with isqrt16(unsigned int) defined: mozzi_fixmath.cpp and mozzi_fixmath.h. I commented out the definition in the cpp file and it compiled.
I have built a Qt toolchain using Yocto. I installed it and set the environment variables running the script generated by Yocto.
I open QtCreator and configure my cross-compiler kit following these instructions.
I'm unable to build this:
#include <QApplication>
#include <QPushButton>
int main(int argc, char **argv)
{
QApplication a( argc, argv );
QPushButton hello( "Hello world!", 0 );
hello.resize( 100, 30 );
hello.show();
return a.exec();
}
Getting this error:
(.qtversion[qt_version_tag]+0x0):-1: error: undefined reference to `qt_version_tag'
So I try to build this instead:
#include <stdio.h>
int main()
{
printf("Hello world!\n");
return 0;
}
It's ok. But when I deploy to my target and try to run it can't because it hasn't been compiled for target architecture (arm).
helloworld: ELF 32-bit LSB executable, Intel 80386, version 1 (SYSV), dynamically linked, interpreter /lib/ldd
There is also this warning which could be very indicative:
:-1: warning: "/usr/bin/gcc" is used by qmake, but "/opt/poky/2.1.1/sysroots/i686-pokysdk-linux/usr/bin/arm-poky-linux-gnueabi/arm-poky-linux-gnueabi-gcc" is configured in the kit.
Please update your kit or choose a mkspec for qmake that matches your target environment better.
I tried to set mkspec on my kit configuration but the result it's the same.
Solved. Maybe I "lied" about saying that setting the mkspec manually it wasn't working neither. That's not true, it does. It's just I was having another issues and couldn't test it properly. The problem was mkspec it wasn't the right. It was pointing to linux-g++ and I fixed it pointing to the proper mkspec. Anyway Qt cretator is telling me that he can't find it! so it's that a bug? The first issue (compiling GUI) was solved too thanks to this.
I wrote a sample program using QSqlDatabase object two years ago with a Qt configuration that depended on static libraries. It compiled ran as expected. Some time last year, I rebuilt the configuration using shared libraries and now I am getting the following errors.
Here is the error:
main.obj : error LNK2019: unresolved external symbol "__declspec(dllimport) publ
ic: __thiscall QSqlDatabase::~QSqlDatabase(void)" (__imp_??1QSqlDatabase##QAE#XZ
) referenced in function _main
...
debug\qtsql.exe : fatal error LNK1120: 12 unresolved externals
Here are my includes and the instantiation of the object in main.cpp:
#include <Qt>
#include <QtDebug>
#include <QtSql\QSqlDatabase>
#include <QFile>
#include <QtSql\QSqlQuery>
#include <QString>
#include <QVariant>
#include <QDate>
int main()
{
QSqlDatabase db = QSqlDatabase::addDatabase("QODBC");
...
Also, here is my .pro file:
TEMPLATE = app
TARGET =
DEPENDPATH += . versions
INCLUDEPATH += .
# Input
SOURCES += main.cpp
# Libraries
QMAKE_LIB_DIR += C:\\Qt\\4.7.0\\lib
I thought that last line in the .pro file would give me a link to any library I might need in Qt. I'm pretty ignorant of what it takes to link to the Qt .dll's.
What am I missing to get the program to see the QSqlDatabase library?
Also, must I specify the library even though I have given it the header file and library directory?
CONFIG += qt
QT += sql
might be missing here (link to qmake docs)
Here is a link to the Qt sql examples. Perhaps you find inspiration/guidance there.
#include <QtCore/QCoreApplication>
#include <QtGui/QLabel>
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
QLabel label("Hello world");
label.show();
return a.exec();
}
I am using QTCreator, I installed QT 4.7 on windows.
Now every time I compile I get this error:
:: error: collect2: ld returned 1 exit status
With mingw32 giving me the following
tmp/obj/debug_shared/main.o: In function `main':
E:\Qt\2010.04\qt\QTHello-build-desktop/../QTHello/main.cpp:6: undefined reference to `_imp___ZN6QLabelC1ERK7QStringP7QWidget6QFlagsIN2Qt10WindowTypeEE'
E:\Qt\2010.04\qt\QTHello-build-desktop/../QTHello/main.cpp:8: undefined reference to `_imp___ZN6QLabelD1Ev'
E:\Qt\2010.04\qt\QTHello-build-desktop/../QTHello/main.cpp:8: undefined reference to `_imp___ZN6QLabelD1Ev'
collect2: ld returned 1 exit status
mingw32-make[1]: *** [debug\QTHello.exe] Error 1
mingw32-make: *** [debug-all] Error 2
The process "E:/Qt/2010.04/mingw/bin/mingw32-make.exe" exited with code %2.
Error while building project QTHello (target: Desktop)
When executing build step 'Make'
Whats the problem??
Create a Qt GUI project and olny then write what you have written.
Your project file is probably not including the required stuff. Do you have either
TEMPLATE = app
or
QT += gui
in your .pro file?
Are you linking with QtGui? If you don't, do it.
Also, for UI applications you must use QApplication. QCoreApplication is for CLI-only tools.
You want to create a Hello World app with QT? Really simple:
Create a new GUI app into QtCreator
Open the ui file and add a label using the QtDesigner embedded into QtCreator
Compile and launch
You have your Hello World application done with Qt
Then if you want to know how to write a QTGui application, just open files in project to see what is written in them.
I am using qt and developing a desktop app that will run under win xp/vista.
I have a 3rd party library UserAgentLib (static, and shared). But I am not sure how to link in qt creator.
I have opened the *.pro file and added my library and header path.
The library is called UserAgentLib and the header file is called UserAgentLib.h
TARGET = Dialer
TEMPLATE = app
LIBS += D:\Projects\qtDialer\tools\lib\UserAgentLib
INCLUDEPATH += D:\Projects\qtDialer\tools\inc
SOURCES += main.cpp\
catdialer.cpp
HEADERS += catdialer.h
FORMS += catdialer.ui
I think it does find the header file, as I get about 100 errors for declarations in the UserAgentLib.h file. However, I don't think it is linking with the library.
Many thanks for any suggestions,
======================
I have create a very simple library in VS C++ 2008. Here is the code for the header and source file.
Header:
// mathslibrary.hpp
int add_numbers(const int a, const int b);
Source:
// mathslibrary.cpp
#include "mathslibrary.hpp"
int add_numbers(const int a, const int b)
{
return a + b;
}
I have compiled this into a library. And tested by linking with a WIN32 console application in VS 2008. The library worked as expected.
Now when I try and link with qt.
#include <QtCore/QCoreApplication>
#include <iostream>
#include "mathslibrary.hpp"
int main(int argc, char *argv[])
{
QCoreApplication a(argc, argv);
std::cout << "add numbers 40 + 60 = " << add_numbers(40, 60) << std::endl;
return a.exec();
}
This is my qmake file:
QT -= gui
TARGET = testlibrary
CONFIG += console
CONFIG -= app_bundle
TEMPLATE = app
LIBS = D:\Projects\TestLibrary\mathsLibrary\Debug\mathsLibrary.lib
INCLUDEPATH = D:\Projects\TestLibrary\mathsLibrary\
SOURCES += main.cpp
These are the errors I get when I try and build:
c:/Qt/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../libmingw32.a(main.o):main.c::-1: error: undefined reference to `WinMain#16'
:-1: error: collect2: ld returned 1 exit status
And these are the compile issues:
Running build steps for project testlibrary...
Creating gdb macros library...
Configuration unchanged, skipping QMake step.
Starting: C:/Qt/mingw/bin/mingw32-make.exe debug -w
mingw32-make: Entering directory `D:/Projects/TestQTLibrary/testlibrary'
C:/Qt/mingw/bin/mingw32-make -f Makefile.Debug
mingw32-make[1]: Entering directory `D:/Projects/TestQTLibrary/testlibrary'
g++ -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -Wl,-subsystem,console -mthreads -Wl -o debug\testlibrary.exe -L"c:\Qt\qt\lib"
D:\Projects\TestLibrary\mathsLibrary\Debug\mathsLibrary.lib -lQtCored4
mingw32-make[1]: Leaving directory `D:/Projects/TestQTLibrary/testlibrary'
mingw32-make: Leaving directory `D:/Projects/TestQTLibrary/testlibrary'
c:/Qt/mingw/bin/../lib/gcc/mingw32/3.4.5/../../../libmingw32.a(main.o):main.c:
(.text+0x104): undefined reference to `WinMain#16'
collect2: ld returned 1 exit status
mingw32-make[1]: * [debug\testlibrary.exe] Error 1
mingw32-make: * [debug] Error 2
Exited with code 2.
Error while building project testlibrary
When executing build step 'Make'
Many thanks for any advice,
Don't know if this changes anything, but maybe you have to define it like this:
LIBS += -LD:/Projects/qtDialer/tools/lib -lUserAgentLib
If you are getting compiler errors then your UserAgentLib.h probably didn't get included. You can test it with:
!exists( UserAgentLib.h ) {
error( "No UserAgentLib.h file found" )
}
You put the above in one of the .pro file and not the constructor.See this.
If the library didn't get linked (which is after your application has compiled well) -- then you need to tinker with your LIBS += ... line, though which appears fine on first glance.
Try this with the simple library first and then try it with the library you are actually trying to get working.
LIBS += D:\Projects\qtDialer\tools\lib\mathsLibrary.lib
In your .hpp file, add extern "C" before your function declarations:
// mathslibrary.hpp
extern "C" int add_numbers(const int a, const int b);
Rebuild the library from Visual Studio.
Now you should be able to compile your test app with Qt Creater. Then copy the corresponding dll into the directory with your new executable and give it a run.
As far as i understood, you generated a dll using MSVC and now you are trying to link it in Qt using mingw. right?
Object files and static libraries created with different compilers, or
even with significantly different releases of the same compiler, often
cannot be linked together. This issue is not specific to MinGW: many
other compilers are mutually incompatible. Build everything from
source with the same version of the same compiler if you can
chech this out : http://chadaustin.me/cppinterface.html