Creating makefile with pthreads

Question

I want to create a makefile that supports posix semaphores. That is what I've got so far:

CFLAGS=-g -ansi -pedantic -Wall -Werror -D_XOPEN_SOURCE=600
LDFLAGS=-pthread 
CC=gcc
OBJECTS=MsgQueueMain.o MsgQueue.o Queue.o MyMalloc.o
TARGET=MsgQueueMain

all: $(TARGET)

$(TARGET): $(OBJECTS)
    $(CC) $(OBJECTS) -o $@

include depends

depends:
    $(CC) -MM $(OBJECTS:.o=.c) > depends

clean:
    rm ./$(TARGET) *.o

For some reason, I'm getting "undefined reference" for all calls to semaphore.h api functions.

Solution

You need to link with the rt or pthread library. From man sem_destroy reference page:

Link with -lrt or -pthread.

Add to the end of the compiler command as order is important (unsure if order is important for -pthread as this defines some macros and adds -lpthread).

As commented by Vlad Lazarenko the LDFLAGS is not part of your TARGET. Change to:

$(CC) $(OBJECTS) -o $@ $(LDFLAGS)

Comments

[Idelic]

This is probably not related to your prolem, but you need -pthread when compiling and linking, so you should add it to CFLAGS as well.

[Admin]

His problem is that LDFLAGS is not specified in his $(TARGET) building command and not because he doesn't know that -pthread is need...

[hmjd]

@VladLazarenko, well spotted. I completely missed that.