Makefile 获取多个子目录中的源文件

Question

I am creating a custom Makefile to to build a C++ Linux application. I have my cpp source files in a folder called src on the same level as the Makefile. So far I have been able to build my object files with the following :

$(OBJ_DIR)/%.o: $(SRC_DIR)/%.cpp | $(OBJ_DIR)
    $(CC) $(CPPFLAGS) $(CFLAGS) -c $< -o $@ 

Now my project is starting to get a bit more complicated and I want subdirectories within src , such as src/common , and also, not every file is a cpp file now but also a c file.

I guess having a separate Makefile for each subdirectory is the best way but I am trying to keep this simple for now with just one Makefile.

I tried the following but doesn't work

$(OBJ_DIR)/%.o: $(SRC_DIR)/%.cpp $(SRC_DIR)/common/%.cpp $(SRC_DIR)/common/%.c | $(OBJ_DIR)
    $(CC) $(CPPFLAGS) $(CFLAGS) -c $< -o $@

I could have the Makefile do a shell find to find all cpp and c files but also trying to avoid this.

I'd appreciate any recommendations.

Answer 1

This:

$(OBJ_DIR)/%.o: $(SRC_DIR)/%.cpp $(SRC_DIR)/common/%.cpp $(SRC_DIR)/common/%.c | $(OBJ_DIR)

cannot work; what it says that if make wants to build some file $(OBJ_DIR)/XXX.o and there is no explicit rule, then if and only if ALL the prerequisites $(SRC_DIR)/XXX.cpp , $(SRC_DIR)/common/XXX.cpp , and $(SRC_DIR)/common/XXX.c exist or can be created by make, then the rule will match.

If the same target could be built from multiple different prerequisites you must create multiple rules, one per prerequisite.

Also, it doesn't make sense to compile both C files ( .c ) and C++ files ( .cpp ) using the same recipe. C++ compilers use the variables CXX and CXXFLAGS and C compilers use the variables CC and CFLAGS .

As for avoiding find , you can't avoid informing make what files you want to be compiled, in some manner. You either have to list them in your makefile explicitly, or else use some method to generate them dynamically. There's no way around this. You don't have to use find if you don't want to; for example if you know that all the files will be either one or two directories down you could use wildcard , like:

SRCS := $(wildcard $(SRC_DIR)/*.cpp $(SRC_DIR)/*.c $(SRC_DIR)/*/*.cpp $(SRC_DIR)/*/*.c)