如何在一个项目中使用gcc编译c文件和使用g++编译hpp

Question

I have C project needs to link opencv library, the c code must compile with gcc, if I compile the project using gcc then it report errors that opencv hpp header file must be compiled as C++. so, any possible to compile c files using gcc and compile hpp files using g++ in one project? or any way to solve my compile problem

I specified rules below in makefile,but it seems not work

$(OBJ_DIR)/%.o: %.hpp
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CXX) -c $(CFLAGS) -o $@ $<

$(OBJ_DIR)/%.o: %.c 
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CC) -c $(CFLAGS) -o $@ $<

$(OBJ_DIR)/%.o: %.cpp
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CXX) -c $(CFLAGS) -o $@ $<

$(OBJ_DIR)/%.o: %.cc
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CXX) -c $(CFLAGS) -o $@ $<

Answer 1

$(OBJ_DIR)/%.o: %.c 
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CC) -c $(CFLAGS) -o $@ $<

Looks OK.

$(OBJ_DIR)/%.o: %.cpp
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CXX) -c $(CFLAGS) -o $@ $<

Not OK. That should be CXXFLAGS (for C++), not CFLAGS (for C).

$(OBJ_DIR)/%.o: %.cc
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CXX) -c $(CFLAGS) -o $@ $<

Same as above. Plus, your project should use either .cc or .cpp, not both.

$(OBJ_DIR)/%.o: %.hpp
    @echo "  COMPILE $(abspath $<)"
    @mkdir -p $(OBJ_DIR)
    @$(CXX) -c $(CFLAGS) -o $@ $<

.hpp files include C++ code, so that is where the error message comes from. But more importantly, header files are included , not compiled to object code, so this whole make rule makes no sense. Your project should work without it (unless you have a different problem elsewhere).

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Your comments indicate that you are somewhat arbitrarily mixing C code compiled with GCC, C code compiled with G++, and C++ code compiled with G++. This is a bad idea and will give you all kinds of problems down the road. C++ and C are somewhat compatible, but different in minor details that can and will come back and bite you. If it's C, compile it as C. If it's C++, compile it as C++. If you want to interface the two, write interfacing code. Don't just mix the codebases.