On Thu, 2022-08-11 at 01:58 +0800, ljh wrote: > I have three c source files: x.c, y.c, z.c and I name x as the target > on left. Can I put x.o in the prerequisites on the right too? Are > they the same, with or without x.o in the prerequisites on the right? > > x: y.o z.o x.o # with x.o
It is correct to do this. These two rules do not behave exactly the same: x: y.o z.o versus x: y.o z.o x.o (you can see the difference for yourself by running "make" both ways) but the result of both of these will give you the same working program. > Is it correct for me to use patsubst function to include all object > files? > x: $(patsubst %.c,%.o,$(wildcard *.c)) This is fine too. > In my test the rule with patsubst works on most cases. But if my code > uses C++20 modules, I need to omit x.o if I want to omit the recipe: > x: y.o z.o # without x.o and recipe > > if I include x.o, I can't omit the recipe: > ` x: y.o z.o x.o ` # with x.o > ` $ (CXX) $ (LDFLAGS) $^ $(LDLIBS) -o $@ ` # with recipe I don't know why you keep referring to C++20 modules. Make doesn't know anything about C++20 modules, it doesn't even know what version of C++ the compiler is building with. It barely even knows that there is such a thing as C++: all it knows is "some source files end in .cpp or .cc or .cxx and those should be built with a recipe that uses variables CXX and CXXFLAGS". In any event, I see no reason why an implicit rule without a recipe and with x.o as a prerequisite wouldn't work. In fact, it works fine for me: $ ls Makefile x.c y.c z.c $ cat Makefile x: $(patsubst %.c,%.o,$(wildcard *.c)) $ make cc -c -o x.o x.c cc -c -o y.o y.c cc -c -o z.o z.c cc x.o y.o z.o -o x
