why “undefined reference to `boost::system::generic_category” even if I do link against boost_system

19
votes

I would understand this error message if I had not put the -lboost_system flag, but it is really here:

g++ -o build/myproject build/main/main.o -L/usr/local/boost/boost_1_52_0/boost/libs -L/usr/lib -Lbuild -L. -lboost_system -lboost_thread -lpthread -lboost_regex -lpq -lmylibrary
build/libmylibrary.a(library.o): In function `__static_initialization_and_destruction_0(int, int)':
library.cpp:(.text+0x25f): undefined reference to `boost::system::generic_category()'
library.cpp:(.text+0x269): undefined reference to `boost::system::generic_category()'
library.cpp:(.text+0x273): undefined reference to `boost::system::system_category()'

Do you have any idea what should I investigate to solve the problem ? (I use gcc 4.6.3)

1
gccboostlinker
try putting it at the end. - user1252091
nooo !? that works ! ! ! do you have any idea why ? - Stephane Rolland
It's explained in the second part of this answer. - user1252091
Even easier, -DBOOST_SYSTEM_NO_DEPRECATED likely makes it unnecessary to link with boost_system at all (stackoverflow.com/a/30877725/1918193). - Marc Glisse
@MarcGlisse Still complains:/home/meir/boost_1_59_0/boost/thread/pthread/thread_data.hpp:278: undefined reference to `boost::this_thread::hiden::sleep_until(timespec const&)' - AlwaysLearning

1 Answers

30
votes

The order at which you link your libraries matters, in your case you have library.cpp that apparently uses the boost_system library

library.cpp:(.text+0x25f): undefined reference to `boost::system::generic_category()'
library.cpp:(.text+0x269): undefined reference to `boost::system::generic_category()'
library.cpp:(.text+0x273): undefined reference to `boost::system::system_category()'

To solve this you should move the boost_system library to the end of your link line

g++ -o build/myproject build/main/main.o -L/usr/local/boost/boost_1_52_0/boost/libs -L/usr/lib -Lbuild -L. -lboost_thread -lpthread -lboost_regex -lpq -lmylibrary **-lboost_system**

Alternatively, build libmylibrary.so as a shared library and link to the boost_system library directly.