strange mingw linker errors with boost? - c++

Question

I've been working on this for a while now, and can't seem to make sense of the situation - partly bceause I don't fully understand what's going on (which is why I came here).
I'm doing a sort of boost hello world as follows:
#include <boost/thread/thread.hpp>
#include <cstdio>
void helloworld() {
std::printf("HELLO FROM A BOOST THREAD!");
}
int main(int argc, char **argv) {
boost::thread t(&helloworld);
t.join();
}
This is on Windows. I stored the Boost directory in C:\Boost. I ran bootstrap and bjam, and now have a stage/lib folder that contains all the .lib files. The lib files relating to the boost/thread library are:
libboost_thread-vc100-mt.lib
libboost_thread-vc100-mt-1_46_1.lib
libboost_thread-vc100-mt-gd.lib
libboost_thread-vc100-mt-gd-1_46_1.lib
Now I compile:
g++ -c main.cpp -I/Boost
that line works fine, I get main.o. Then:
g++ -o test.exe main.o -L/Boost/stage/lib -llibboost_thread-vc100-mt
And that's where the trouble happens. First of all, If I didn't type the -l argument the way I did, MinGW couldn't even find the file. Meaning, if I tried:
-lboost_thread-vc100-mt
instead of the way I typed it above (and how I thought it should be done), ld would exit with no such file. Anyway, this is now the output I'm getting from that line:
main.o:main.cpp:(.text+0x47): undefined reference to `_imp___ZN5boost6thread4joinEv'
main.o:main.cpp:(.text+0x55): undefined reference to `_imp___ZN5boost6threadD1Ev'
main.o:main.cpp:(.text+0x70): undefined reference to `_imp___ZN5boost6threadD1Ev'
main.o:main.cpp:(.text$_ZN5boost6threadC1IPFvvEEET_NS_10disable_ifINS_14is_convertibleIRS4_NS_6detail13thread_move_tIS4_EEEEPNS0_5dummyEE4typeE[boost::thread::thread<void (*)()>(void (*)(), boost::disable_if<boost::is_convertible<void (*&)(), boost::detail::thread_move_t<void (*)()> >, boost::thread::dummy*>::type)]+0x23): undefined reference to `_imp___ZN5boost6thread12start_threadEv'
collect2: ld returned 1 exit status
Now somewhere in there, I can tell that these are apparently the functions I'm supposed to be getting from boost/thread, and apparently it does find the lib file, so why isn't it linking correctly?
Thank you very much for any help!
EDIT:
I've rebuilt boost using the bjam "stage" option
bjam toolset=gcc stage
Now, after the build completes, I'm left with a stage/lib folder with .a files, as is to be expected. These are the boost/thread related libraries:
libboost_thread-mgw45-mt-1_46_1.a
libboost_thread-mgw45-mt-d-1_46_1.a
However, linking as follows:
g++ -o test.exe main.o -L/Boost/stage/lib -lboost_thread-mgw45-mt-1_46_1
outputs the exact same errors. Also tried:
g++ -o test.exe main.o -L/Boost/stage/lib -lboost_thread-mgw45-mt-1_46_1 -static
I'm at a loss, still.

Answer 1

Solved the problem. Boost's headers are configured to be dynamically linked, but the dynamic libraries (dll's) are not built unless you specify:
--build-type=complete
when invoking bjam. After that, copy the appropriate dll to your application directory, but still use the
-L/BOOST_DIR/stage/lib -lname
when linking.

Answer 2

This set of library files:
libboost_thread-vc100-mt.lib
libboost_thread-vc100-mt-1_46_1.lib
libboost_thread-vc100-mt-gd.lib
libboost_thread-vc100-mt-gd-1_46_1.lib
are for the Visual Studio 2010 compiler. They won't work with GCC. If you want to use gcc/MinGW, you'll need to download/build a set of boost libraries for that compiler. Alternatively you can install VS 2010 and use that compiler (the free VC++ 2010 Express version should work fine if cost is an issue).
You can get a MinGW distribution with Boost already in the package from http://nuwen.net/mingw.html (32-bit target only, I believe).
To answer about getting the errors with using the MinGW libs:
The _imp_ prefixes on the symbols is an indication that g++ is looking to link to a a dll/shared library. The .lib file you have are for static libraries (which is what also what I get when doing a straightforward bjam build of the libraries). If you look in boost/thread/detail/config.hpp you'll see that for Win32 builds it defaults to building against a DLL library unless the MSVC or Intel compiler is being used.
I'm not even sure exactly how to build the DLL libraries - I'll have to look it up. In the meantime, you can use the following command to build your example such that it'll link against the static library. The BOOST_THREAD_USE_LIB macro build the .cpp file such that it'll expect to link against the static library:
g++ -I/Boost -DBOOST_THREAD_USE_LIB -c main.cpp