Compiling C++ source file using Boost.Thread - c++

Question

I am trying to learn how to use the C++ Boost.Thread library. I have installed the Boost libraries on my Ubuntu 11.10 system. I am following the book "The Boost C++ Libraries" by Schaling - specifically example 6.1 on page 66. I am trying to compile the following code example:
#include <boost/thread.hpp>
#include <iostream>
void wait(int seconds)
{
boost::this_thread::sleep(boost::posix_time::seconds(seconds));
}
void thread()
{
for(int i = 0; i < 5; ++i)
{
wait(1);
std::cout << i << std::endl;
}
}
int main()
{
boost::thread t(thread);
t.join();
}
However, when I compile this with the following from the command line:
$ g++ example61.cpp -o example61 -I /usr/local/include
I get the following output:
/tmp/cc6bVu1F.o: In function `main':
example6.cpp:(.text+0x9d): undefined reference to `boost::thread::join()'
example6.cpp:(.text+0xae): undefined reference to `boost::thread::~thread()'
example6.cpp:(.text+0xc6): undefined reference to `boost::thread::~thread()'
/tmp/cc6bVu1F.o: In function `boost::detail::thread_data_base::thread_data_base()':
example6.cpp:(.text._ZN5boost6detail16thread_data_baseC2Ev[_ZN5boost6detail16thread_data_baseC5Ev]+0x24): undefined reference to `vtable for boost::detail::thread_data_base'
/tmp/cc6bVu1F.o: In function `void boost::this_thread::sleep<boost::posix_time::seconds>(boost::posix_time::seconds const&)':
example6.cpp:(.text._ZN5boost11this_thread5sleepINS_10posix_time7secondsEEEvRKT_[void boost::this_thread::sleep<boost::posix_time::seconds>(boost::posix_time::seconds const&)]+0x35): undefined reference to `boost::this_thread::sleep(boost::posix_time::ptime const&)'
/tmp/cc6bVu1F.o: In function `boost::thread::thread<void (*)()>(void (*)(), boost::disable_if<boost::is_convertible<void (*&)(), boost::detail::thread_move_t<void (*)()> >, boost::thread::dummy*>::type)':
example6.cpp:(.text._ZN5boost6threadC2IPFvvEEET_NS_10disable_ifINS_14is_convertibleIRS4_NS_6detail13thread_move_tIS4_EEEEPNS0_5dummyEE4typeE[_ZN5boost6threadC5IPFvvEEET_NS_10disable_ifINS_14is_convertibleIRS4_NS_6detail13thread_move_tIS4_EEEEPNS0_5dummyEE4typeE]+0x30): undefined reference to `boost::thread::start_thread()'
/tmp/cc6bVu1F.o: In function `boost::detail::thread_data<void (*)()>::~thread_data()':
example6.cpp:(.text._ZN5boost6detail11thread_dataIPFvvEED2Ev[_ZN5boost6detail11thread_dataIPFvvEED5Ev]+0x1f): undefined reference to `boost::detail::thread_data_base::~thread_data_base()'
/tmp/cc6bVu1F.o:(.rodata._ZTIN5boost6detail11thread_dataIPFvvEEE[typeinfo for boost::detail::thread_data<void (*)()>]+0x10): undefined reference to `typeinfo for boost::detail::thread_data_base'
collect2: ld returned 1 exit status
I don't know how to interpret this. Can anyone help? Thank you so much!

Answer 1

That is a linking error. It means your code is correct and you include the correct headers, but the compiler doesn't link against the boost threading library. To fix this, you need to compile like this:
g++ example61.cpp -o example61 -I /usr/local/include -lboost_thread
If you've installed the Boost threading library to a non-standard path, you must also add it to the search path:
g++ example61.cpp -o example61 -I /usr/local/include -lboost_thread -L/usr/local/lib

Answer 2

You need to link with the library. Some Boost libraries are implemented entirely in the header files and do not need a library. But others, like thread, are implemented partly in headers and partly in compiled library code.
I believe that you need to add -lboost_thread-mt to your compile command.

Answer 3

Boost thread are not a template only library. You need to add a -lboost_thread while linking /compiling.
Most of the libraries in boost are implemented in headers. They can simply be included like you have done. Boost thread on the other hand, is of such a nature that you need to depend on its compiled units, only the declaration of its function are readily available to you in the header. So the compiler, or more correctly the linker, which is responsible for linking your calls to the declared functions /classes need to know where to look for these symbols. By invoking the compiler with a -lboost_thread you tell it to link to the library (-l) boost thread.

Answer 4

Following your comments I share with you compilation string for pocketcpp compilation tool:
g++ -static -I"\boost" "$(FULL_CURRENT_PATH)" -L"\MinGW\lib" -lboost_thread -lboost_system -o "$(CURRENT_DIRECTORY)\$(NAME_PART).exe"
Good luck,

Answer 5

I commented above, but wanted to share the full command line here.
g++ -std=c++11 thread_example.cpp -lboost_thread -lboost_system
[I'm using thread_example.cpp as the source filename; please replace with your own]