QT/mingw32 undefined reference errors... unable to link a .lib

Question

Hello, I am new to QT and have one error I am unable to fix...

I have a bunch of windows (VS2005) static library file (.lib). And I am testing if they work well with QT. So I took the most simple library that I have. (Called "MessageBuffer").

So I added MessageBuffer.h to the main.cpp, and added the location of thoses file in the INCLUDEPATH of the .pro

Until then everything seem fine, I can use the class and QT IDE show all method and everything. So to me it look like it found the .h file.

Now I added the MessageBuffer.lib (VS2005/Debug build) in the .pro like this:

LIBS += E:/SharedLibrary/lib/MessageBufferd.lib

I have also tried the following: win32:LIBS += E:/SharedLibrary/lib/MessageBufferd.lib LIBS += -LE:/SharedLibrary/lib -lMessageBufferd win32:LIBS += -LE:/SharedLibrary/lib -lMessageBufferd

Here is the content of my pro file:

QT += opengl
TARGET = SilverEye
TEMPLATE = app
INCLUDEPATH += E:/SharedLibrary/MessageBuffer
SOURCES += main.cpp \
    silvereye.cpp
HEADERS += silvereye.h
FORMS += silvereye.ui
OTHER_FILES += 
win32:LIBS += E:/SharedLibrary/lib/MessageBufferd.lib

They all give me the same errors: (and I get the same even if I don't include the .lib)

Running build steps for project SilverEye...
Configuration unchanged, skipping QMake step.
Starting: C:/Qt/2009.03/mingw/bin/mingw32-make.exe -w 
mingw32-make: Entering directory `C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye'
C:/Qt/2009.03/mingw/bin/mingw32-make -f Makefile.Debug
mingw32-make[1]: Entering directory `C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye'
g++ -enable-stdcall-fixup -Wl,-enable-auto-import -Wl,-enable-runtime-pseudo-reloc -mthreads -Wl -Wl,-subsystem,windows -o debug\SilverEye.exe debug/main.o debug/silvereye.o debug/moc_silvereye.o -L"c:\Qt\2009.03\qt\lib" -lopengl32 -lglu32 -lgdi32 -luser32 -lmingw32 -lqtmaind E:/SharedLibrary/lib/MessageBufferd.lib -lQtOpenGLd4 -lQtGuid4 -lQtCored4
mingw32-make[1]: Leaving directory `C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye'
mingw32-make: Leaving directory `C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye'
debug/main.o: In function `Z5qMainiPPc':
C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye/main.cpp:12: undefined reference to `MessageBuffer::MessageBuffer()'
C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye/main.cpp:13: undefined reference to `MessageBuffer::Append(char*, int)'
C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye/main.cpp:17: undefined reference to `MessageBuffer::~MessageBuffer()'
C:/Documents and Settings/JP/My Documents/QTProjects/SilverEye/main.cpp:17: undefined reference to `MessageBuffer::~MessageBuffer()'
collect2: ld returned 1 exit status
mingw32-make[1]: *** [debug\SilverEye.exe] Error 1
mingw32-make: *** [debug] Error 2
Exited with code 2.
Error while building project SilverEye
When executing build step 'Make'

Can anyone help please...

Answer 1

I assume that you have used the MessageBuffer library in another application with problems. The error looks like it either cannot find the library or the MessageBuffer class is not being exported.

Have you tried putting -l on front of the library in the pro file?

win32:LIBS += -lE:/SharedLibrary/lib/MessageBufferd.lib

See my other answer. I added the other answer because I didn't want to make this answer any more messy than it already was.

Tried so far:

• Not a typo, d is appended to the library
• Using the lib extension is correct as seen in the output

Answer 2

Based on the question Use libraries compiled with visual studio in an application compiled by g++ (mingw) and the MSDN forum post I can't mix VC & GCC it does not appear you can link a gcc application with visual c++ compiled libraries.

The solution would be to recompile everything with the same compiler.

Answer 3

The MinGW FAQ discusses this problem and offers a solution:

1. Create a definition file using reimp (for lib files) or pexports (for dll files).
2. Remove the underscore prefixes from the stdcall functions.
3. Use dlltool to convert the MSVC library into a MinGW library with the new definition.

That didn’t work. We finally removed the ordinals from the function names, which caused it to compile. But the program wouldn’t run because it couldn’t find the linked functions in the DLL. Finally, after consulting the MSDN documentation for definition files, we changed the build instructions:

1. Create a definition file using reimp.
2. For each stdcall function (formatted as _name@ordinal) add a line name = _name@ordinal, allowing MinGW to map its stdcall naming convention to that of MSVC.
3. Use dlltool to convert the MSVC library into a MinGW library with the new definition.

It worked! To compile the project you must simply:

1. Download and install the Qt/Windows package, which includes MinGW.
2. Download reimp and drop it into the MinGW/bin folder.
3. Download the development packages for the third-party libraries and point an environment variable to that location.
4. Build the project with the usual qmake/make commands.

Taken from: http://blog.outofhanwell.com/2006/05/01/linking-msvc-libraries-with-mingw-projects/