undefined reference to `pthread_key_create' (linker error)

Question

I have downloaded gtest 1.7.0 sources from here:

https://code.google.com/p/googletest/downloads/list

and build the gtest .a files (lib files) on ubuntu 13.10

Answer 1

Use -pthread instead of -lpthread (for linking with pthread-library), while you using gtest in your executable.

OR

Move the -lpthread after libgtest.a (sequence matters).

Answer 2

To answer we probably need more information, are you on a 64 bit machine and downloaded a 32 bit library?

Answer 3

You need to specify -pthread after -lgtest. The linker takes libraries in order, and only takes as much as it needs to resolve references which are undefined at that point.

Answer 4

The option -lgtest is attempting to link the dynamic library libgtest.so. You wish to link the static library /home/user/gtest-1.7.0/lib/.libs/libgtest.a.

Instead of:

g++ main.cpp -I/home/user/gtest-1.7.0/include -L/home/user/gtest-1.7.0/lib/.libs -lgtest -pthread

use:

g++ main.cpp -I/home/user/gtest-1.7.0/include /home/user/gtest-1.7.0/lib/.libs/libgtest.a -pthread

Note that your commandline supplies no name for the resulting executable, which will default to a.out. If you want it called, e.g. mytest, then do:

g++ -o mytest main.cpp -I/home/user/gtest-1.7.0/include /home/user/gtest-1.7.0/lib/.libs/libgtest.a -pthread

Answer 5

Nope, the problem is with Gtest's build.

If you build it using the standard configure approach, it isn't supplying the -lpthread correctly to create libgtest.so. Hence, when you try building a final shared library that actually uses the pthread capability it fails.

Instead, use the Cmake approach:

cd gtest-1.7.0
mkdir build
cd build
cmake -DBUILD_SHARED_LIBS=ON ..
make 

And then manually install these into /usr/lib/

This version correctly links in libpthread into libgtest.