Why am I getting undefined reference to pthread_mutexattr_settype?

Question

I am trying to compile and link a sample file from the Novell LDAP C SDK but the link is failing due to 3 unresolved symbols in the pthread library. I am using gcc 4.8.1 on Ubuntu 13.10 (Saucy). I have properly included the pthread library as the last library on the command line, but these particular symbols are still not being resolved.

$ gcc -Wl,-trace-symbol=pthread_mutexattr_settype -Wl,-trace-symbol=pthread_mutexattr_init   -Wl,-trace-symbol=pthread_mutex_trylock  -o search search.o -L../lib -lldapsdk -lpthread

../lib/libldapsdk.so: reference to pthread_mutexattr_settype<br>
../lib/libldapsdk.so: reference to pthread_mutexattr_init<br>
../lib/libldapsdk.so: reference to pthread_mutex_trylock<br>
/lib/i386-linux-gnu/libpthread.so.0: definition of pthread_mutexattr_settype<br>
/lib/i386-linux-gnu/libpthread.so.0: definition of pthread_mutexattr_init<br>
/lib/i386-linux-gnu/libpthread.so.0: definition of pthread_mutex_trylock<br>
../lib/libldapsdk.so: undefined reference to pthread_mutexattr_settype<br>
../lib/libldapsdk.so: undefined reference to pthread_mutex_trylock<br>
../lib/libldapsdk.so: undefined reference to pthread_mutexattr_init<br>
collect2: error: ld returned 1 exit status

$ readelf --all  /lib/i386-linux-gnu/libpthread.so.0|grep pthread_mutexattr_settype<br>
   114: 00009d90    36 FUNC    GLOBAL DEFAULT   13 pthread_mutexattr_settype@@GLIBC_2.1<br>
   493: 00009d90    36 FUNC    GLOBAL DEFAULT   13 pthread_mutexattr_settype

Please try passing `-pthread` to the compiler (without the `-l`). See also [gcc - significance of -pthread flag when compiling](http://stackoverflow.com/q/2127797/341970). — Ali, Mar 04 '14 at 19:15
Ali added his comment as an answer, so might like to accept it as it seems to answer your question. — alk, May 05 '14 at 14:04

score 31 · Answer 1 · edited May 23 '17 at 12:24

31

_{Just writing up the comment as an answer as it proved to be helpful based on other users' feedback.}

Please pass -pthread to the compiler (without the -l). See also gcc - significance of -pthread flag when compiling.

edited May 23 '17 at 12:24

Community

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answered May 05 '14 at 13:42

Ali

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Why? What's the difference between `-pthread` and `-lpthread`? Thanks for the solution though, it worked for me as well. – TheNotMe May 28 '16 at 11:57

John · Answer 2 · 2017-05-25T07:27:23.763

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In cmake you can addset( CMAKE_CXX_FLAGS " -pthread " )

Do not edit spacing!

edited May 25 '17 at 07:27

answered May 25 '17 at 07:15

John

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Works like a charm. Thanks :) – curiouscupcake Nov 26 '18 at 23:17
In my case, I used set(CMAKE_C_FLAGS " -pthread ") ... and it solved my headache. Merlin's beard !!! – BaldDude Mar 25 '21 at 19:33
I used add_compile_options(-pthread) and add_link_options(-pthread) for cmake. – David Bradley Jul 04 '23 at 12:23

Why am I getting undefined reference to pthread_mutexattr_settype?

2 Answers2