如何在C++ Makefile中处理.cpp与.cxx混合源文件的规则？

Great start on structuring your Makefile with separate source and object directories! Let's build out the rules to handle both .cpp and .cxx files smoothly. Here's a step-by-step breakdown and complete example:

1. Collect All Source Files #

First, we'll grab every .cpp and .cxx file across your source subfolders using wildcard and foreach:

# Collect all .cpp and .cxx sources across all source subfolders
SRCS = $(foreach dir, $(SRCSUBFOLDERS), $(wildcard $(dir)/*.cpp $(dir)/*.cxx))

2. Map Sources to Object Files #

Next, convert those source paths to corresponding .o files in your OBJDIR (replacing src/ with obj/ and swapping the source extensions for .o):

# Convert source files to object files (preserve directory structure)
OBJS = $(patsubst $(SRCDIR)/%.cpp, $(OBJDIR)/%.o, $(filter %.cpp, $(SRCS))) \
       $(patsubst $(SRCDIR)/%.cxx, $(OBJDIR)/%.o, $(filter %.cxx, $(SRCS)))

3. Ensure Object Directories Exist #

We need to make sure all the subdirectories in OBJDIR exist before compiling. Use an order-only prerequisite (the | syntax) so Make doesn't recompile files just because the directory was touched:

# Create object subdirectories if they don't exist
$(OBJSUBFOLDERS):
	mkdir -p $@

4. Compilation Rules for Both Extensions #

Write pattern rules to handle compiling .cpp and .cxx files separately (they'll use the same compiler flags, since both are C++ sources):

# Compiler and flags (adjust these to your project needs)
CXX = g++
CXXFLAGS = -Wall -Wextra -g -O2

# Rule for .cpp -> .o
$(OBJDIR)/%.o: $(SRCDIR)/%.cpp | $(OBJSUBFOLDERS)
	$(CXX) $(CXXFLAGS) -c $< -o $@

# Rule for .cxx -> .o
$(OBJDIR)/%.o: $(SRCDIR)/%.cxx | $(OBJSUBFOLDERS)
	$(CXX) $(CXXFLAGS) -c $< -o $@

5. Link the Executable #

Finally, add a rule to link all your object files into the final executable:

# Define your target executable name
TARGET = my_project

# Link object files to create the executable
$(TARGET): $(OBJS)
	$(CXX) $(CXXFLAGS) $^ -o $@

6. Add a Clean Rule #

Don't forget a clean rule to tidy up object files and the executable:

# Phony target to avoid conflicts with files named "clean"
.PHONY: clean
clean:
	rm -rf $(OBJDIR) $(TARGET)

Full Combined Makefile #

Here's how it all fits with your existing setup:

# Folders
SRCDIR = src
OBJDIR = obj
SUBFOLDERS = test test/test2
OBJSUBFOLDERS = $(OBJDIR) $(addprefix $(OBJDIR)/, $(SUBFOLDERS))
SRCSUBFOLDERS = $(SRCDIR) $(addprefix $(SRCDIR)/, $(SUBFOLDERS))

# Collect sources
SRCS = $(foreach dir, $(SRCSUBFOLDERS), $(wildcard $(dir)/*.cpp $(dir)/*.cxx))
# Map to objects
OBJS = $(patsubst $(SRCDIR)/%.cpp, $(OBJDIR)/%.o, $(filter %.cpp, $(SRCS))) \
       $(patsubst $(SRCDIR)/%.cxx, $(OBJDIR)/%.o, $(filter %.cxx, $(SRCS)))

# Compiler setup
CXX = g++
CXXFLAGS = -Wall -Wextra -g -O2

# Target executable
TARGET = my_project

# Create object directories
$(OBJSUBFOLDERS):
	mkdir -p $@

# Compile .cpp files
$(OBJDIR)/%.o: $(SRCDIR)/%.cpp | $(OBJSUBFOLDERS)
	$(CXX) $(CXXFLAGS) -c $< -o $@

# Compile .cxx files
$(OBJDIR)/%.o: $(SRCDIR)/%.cxx | $(OBJSUBFOLDERS)
	$(CXX) $(CXXFLAGS) -c $< -o $@

# Link target
$(TARGET): $(OBJS)
	$(CXX) $(CXXFLAGS) $^ -o $@

# Cleanup
.PHONY: clean
clean:
	rm -rf $(OBJDIR) $(TARGET)

This setup will automatically find all your .cpp and .cxx files, compile them to the correct object directories, and link everything into your target executable. Adjust CXXFLAGS and TARGET to match your project's needs!

内容的提问来源于stack exchange，提问作者code_fodder