Link .h files and .c files from different directory using makefile

Question

I'm trying to compile a program called um from a current folder with um.c and include some external implementations. The .h files are in one directory but the .c files implementing these .h files are in a different directory. Below is my makefile. It seems that the compiler knows where to look for the .h file. However, the linker fails and produces the error:

ld: symbol(s) not found for architecture x86_64
clang: fatal error: linker command failed with exit code 1

Makefile:

# define the C compiler to use
CC = gcc

# define any compile-time flags
CFLAGS = -g -O -Wall -Wextra -Werror -Wfatal-errors -std=c99 -pedantic

# define any directories containing header files other than /usr/include
INCLUDES = -I/Users/nguyenmanhduc/Documents/C\ library/cii/include

# define library paths in addition to /usr/lib
LFLAGS = -L/Users/nguyenmanhduc/Documents/C\ library/cii/src

# define any libraries to link into executable:
LIBS = -lm

# define the C source files
SRCS = um.c

# define the C object files 
OBJS = $(SRCS:.c=.o)

# define the executable file 
MAIN = um

.PHONY: depend clean

all:    $(MAIN)
    @echo  Simple compiler named um has been compiled

$(MAIN): $(OBJS) 
    $(CC) $(CFLAGS) $(INCLUDES) -o $(MAIN) $(OBJS) $(LFLAGS) $(LIBS)

.c.o:
    $(CC) $(CFLAGS) $(INCLUDES) -c $<  -o $@

clean:
    $(RM) *.o *~ $(MAIN)

depend: $(SRCS)
    makedepend $(INCLUDES) $^

This question might seem weird because I have little experience with makefile but is there a way that I can link .h and .c files in different folders using makefile.

Thanks!

Answer 1

The problem here is not that your additional .c files are in different directories: it's that you didn't tell your Makefile that they exist at all !

Here's where you list the source inputs (I guess you didn't see the comment?):

# define the C source files
SRCS = um.c

Add the other .c files whose compiled .o s are what you want to link.

For example:

# define the C source files
SRCS = um.c ../wot.c ../hah/lol.c

There is no hard and fast rule but, the way you've constructed this Makefile, those relative paths should resolve just fine.

Answer 2

You don't link .c files, you link .o files.

You appear to be stating is that some of your .c files are in a different directory.

No matter, you have to explicitly list those .c files, in your makefile, just like you are listing the .c files in the directory with the makefile. You have to compile the .c files in a different directory, and then link them, just like you're compiling and linking the .c files in the same directory as the makefile. They're not going to compile themselves.

Another approach would be to have a separate makefile in that other directory, that compiles and builds an archive library, and then in this directory link with that archive library.