Linker errors in compiling a simple pthread code under MingW

Question

I am trying to compile a single c++ source file test.cpp, which has a very simple code which demonstrates pthread_create(); pthread_cond_signal/pthread_cond_wait() functionality.

I have installed Mingw / Ansys on Windows XP where I am working. In the MingW prompt I do:

g++ -IC:/MinGW/include/ -lpthread test.cpp 
//-IC:/MinGW/include to get pthread.h
//-LC:/MinGW/bin to get pthreadGC2.dll

The cpp includes pthread.h as:

#include <pthread.h>

But this gave me multiple linker undefined reference errors to all pthread library functions.

What am I doing wrong here. Is it possible to build a pthread code on MingW environment on windows or not?

How to resolve this errors?

C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x23): undefined reference to `_imp__pthread_mutex_lock'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x67): undefined reference to `_imp__pthread_cond_signal'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x75): undefined reference to `_imp__pthread_mutex_unlock'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x98): undefined reference to `_imp__pthread_exit'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0xbc): undefined reference to `_imp__pthread_mutex_lock'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0xe8): undefined reference to `_imp__pthread_cond_wait'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x10f): undefined reference to `_imp__pthread_mutex_unlock'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x135): undefined reference to `_imp__pthread_exit'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x153): undefined reference to `_imp__pthread_attr_init'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x169): undefined reference to `_imp__pthread_mutex_init'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x17f): undefined reference to `_imp__pthread_attr_setdetachstate'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x195): undefined reference to `_imp__pthread_cond_init'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x1bc): undefined reference to `_imp__pthread_create'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x1e3): undefined reference to `_imp__pthread_create'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x201): undefined reference to `_imp__pthread_join'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x21f): undefined reference to `_imp__pthread_join'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x239): undefined reference to `_imp__pthread_mutex_destroy'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x247): undefined reference to `_imp__pthread_cond_destroy'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x255): undefined reference to `_imp__pthread_attr_destroy'
C:\DOCUME~1\ADESHP~1\LOCALS~1\Temp\ccUQhu7D.o:pthread_cond.c:(.text+0x263): undefined reference to `_imp__pthread_exit'
collect2: ld returned 1 exit status

Answer 1

You need to specify the library on the gcc/g++ command line after the files that depend on the library. So try:

g++ -IC:/MinGW/include/ test.cpp -lpthread

I kicked myself when I stumbled on the answer (it's kind of a FAQ for libraries and gcc). For most gcc options order doesn't matter, but for libraries it's critical.

You should not have to specify the library path if the pthread library came with your MinGW distribution (as it seems is the case for you). Also, remember that the command line above will produce an a.exe executable; pass -o test.exe to avoid that.