Makefile: Wildcard for two programs with different source files - makefile

Question

I'm working on a C project with two programs, a server and a client.
My projects structure:
.
+--/bin
| +--/client
| +--/server
|
+--/lib
| +--header1.h
| +--header2.h
| +--header3.h
|
+--/obj
| +--/client
| +--/server
|
+--/src
| +--/client
| | +--files.c
| +--/server
| +--otherfiles.c
|
+--Makefile
Now I'm stuck on the Makefile, both my programs need different and some overlapping headers. I tried looking into other projects/repositories, but that didn't help me.
This is what i currently got:
SOURCES_CLIENT = ${wildcard src/client/files.c}
SOURCES_SERVER = ${wildcard src/client/otherfiles.c}
HEADERS_CLIENT = ${wildcard lib/header1.h lib/header2.h}
HEADERS_SERVER = ${wildcard lib/header2.h lib/header3.h}
OBJ_CLIENT = ${SOURCES_CLIENT:.c=.o}
OBJ_SERVER = ${SOURCES_SERVER:.c=.o}
CC = gcc
CFLAGS = #not relevant
all: client server
client: ${OBJ_CLIENT}
${CC} -o $# $^
server: ${OBJ_SERVER}
${CC} -o $# $^
How would I create wildcard rules to convert my source files to object files (in the correct bin/ directory) using the corresponding header files? Also my Makefile seems to be optimizable, if so how?

Answer 1

I suppose your base variable definitions must actually look more like this:
SOURCES_CLIENT = ${wildcard src/client/*.c}
SOURCES_SERVER = ${wildcard src/server/*.c}
HEADERS_CLIENT = ${wildcard lib/client*.h}
HEADERS_SERVER = ${wildcard lib/server*.h}
One of the very first things you need to understand about make is that it knows just about nothing about build tools, directories, or files. It just manipulates strings, and chooses a subset of the strings it works with and forms to issue as shell commands, with timing and order governed by the ruleset expressed to it.
Among the implications is that if you want to build a given target then you have to write a rule for exactly that target. In particular, when you run make from the root directory of your project, the wanted binaries (in your scheme) are not client and server, they are bin/client and bin/server. Similarly, the wanted object file corresponding to src/client/files.c is not files.o or src/client/files.o but rather obj/client/files.o.
Having understood that, the next order of business is to define the object file lists correctly. You seem deeply committed to GNU make already, which makes things easier (at some cost in portability). Instead of your current definitions for OBJ_CLIENT and OBJ_SERVER, which provide for object files in a different location than you require, something using a (GNU-specific) substitution reference like this would work:
OBJ_CLIENT = $(SOURCES_CLIENT:src/client/%.c=obj/client/%.o)
OBJ_SERVER = $(SOURCES_SERVER:src/server/%.c=obj/server/%.o)
Having done that, however, you'll need to write explicit rules for building the object files; make's default rules do not handle the needed cross-directory correspondence. You can use GNU pattern rules effectively for this purpose. This is also where you would introduce the dependencies on the headers:
obj/client/%.o: src/client/%.c $(HEADERS_CLIENT)
$(CC) $(CPPFLAGS) $(CFLAGS) -c $< -o $#
Again taking into account the fact that you must provide build rules naming the targets you actually want to build, you might put this all together as:
SOURCES_CLIENT = $(wildcard src/client/*.c)
SOURCES_SERVER = $(wildcard src/server/*.c)
HEADERS_CLIENT = $(wildcard lib/client*.h)
HEADERS_SERVER = $(wildcard lib/server*.h)
OBJ_CLIENT = $(SOURCES_CLIENT:src/client/%.c=obj/client/%.o)
OBJ_SERVER = $(SOURCES_SERVER:src/server/%.c=obj/server/%.o)
CC = gcc
CFLAGS = #not relevant
all: bin/client bin/server
bin/client: $(OBJ_CLIENT)
$(CC) $(CFLAGS) -o $# $^
bin/server: $(OBJ_SERVER)
$(CC) $(CFLAGS) -o $# $^
obj/client/%.o: src/client/%.c $(HEADERS_CLIENT)
$(CC) $(CPPFLAGS) $(CFLAGS) -c $< -o $#
obj/server/%.o: src/server/%.c $(HEADERS_SERVER)
$(CC) $(CPPFLAGS) $(CFLAGS) -c $< -o $#

Answer 2

These two rules should do what you're after
obj/client/%.o: src/client/%.c $(HEADERS_CLIENT)
$(CC) -c -o $# $<
obj/server/%.o: src/server/%.c $(HEADERS_SERVER)
$(CC) -c -o $# $<