CODEWITHSUNDEEP
compilationg++makefile
user1539179
user1539179

Reputation: 1885

g++: fatal error: cannot specify -o with -c, -S or -E with multiple files

I am trying to compile a library file using other library files. I am using the following line in my makefile to create gameobject.o:

lib/gameobject.o: src/gameobject.cpp src/vector.hpp lib/objectevent.o lib/sprite.o
g++ $^ -c -o $@ $(SFML_FLAGS)

All the dependencies comile correctly, but I get the following error when it tries to compile gameobject.o:

g++: fatal error: cannot specify -o with -c, -S or -E with multiple files

I'm still a bit new to using make/separating compilation, so I'm not quite sure what I should do. Do I just have to compile it without setting an output? Do I have to compile gameobject.o without using any of my other .o files? If that's true, wouldn't compile times get pretty big for large objects if you can't compile libraries with other libraries? Or am I just reading this error completely wrong?

Upvotes: 16

Views: 21851

Answers (3)

ram4279
ram4279

Reputation: 31

You can create only one object .o file from one source file. If you are using makefile to build the project. Make sure you are doing $< instead of $^

# Correct one
%.o: %.cpp
    $(CPP) $(CFLAGS) -c -o $@ $<


# InCorrect one
%.o: %.cpp
    $(CPP) $(CFLAGS) -c -o $@ $^

Upvotes: 1

Majid
Majid

Reputation: 517

I had the same problem after I combined some projects of a solution to a single one. I find out there was tow .cpp files with same names and after I did rename one of them It solved.

Upvotes: 1

MadScientist
MadScientist

Reputation: 101051

You're not building a library file here. A .o file is an object file. Typically there is one object file per source file. When you use the compiler's -c option, it takes a single source file and compiles it into a single object file. You cannot add other object files into an existing object file, so adding both .o and .cpp files into the same compiler line with -c is not going to work.

If you want to create a library, that would be something like libfoo.a (the "a" here stands for "archive"). If you want to create an executable you can do that as well.

You need to be more clear about exactly what result you want before we can describe how to get it.

Upvotes: 16

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