gcc cannot specify -o with -c or -S with Multiple files

Question

Whenever I am trying to build something like this in my Makefile -

gcc -o main.o -IStarterWare_Files -c main.c StarterWare_Files/test.h StarterWare_Files/add.h

It throws me error that gcc: cannot specify -o with -c or -S with multiple files. Basically I want my makefile to build the target again if I change for example some macro in one of my header files. My current Makefile is -

EXE    = nextgenrsm
CC     = gcc
LIBS   = StarterWare_Files/
CPPFLAGS = _IStarterWare_Files/


MAIN_OBS = $(patsubst %.c,%.o,$(wildcard *.c))
LIB_OBS  = $(patsubst %.c,%.o,$(wildcard StarterWare_Files/*.c))

all: $(EXE)

$(EXE): $(MAIN_OBS) $(LIB_OBS)
    $(CC) -o $@ $(LDFLAGS) $(MAIN_OBS) $(LIB_OBS) $(LDLIBS)

%.o: %.c 
    $(CC) -o $@ -MD -MP $(CPPFLAGS) $(CFLAGS) -c $^

ALL_DEPS = $(patsubst %.o,%.d,$(MAIN_OBS), $(LIB_OBS))
-include $(ALL_DEPS)

clean:
    rm -f $(LIB_OBS) $(EXE) $(MAIN_OBS) $(ALL_DEPS)

.PHONY: all clean

I can't figure out what changes to make to build my executable again if one of the header files is modified. I don't want to do make clean and make again.

Why are you compiling header files? I think you want to change $^ to just $< so that your %.o: %.c rule only adds the first prerequisite (the source file) to the command, not all its header dependencies as well. — Jonathan Wakely
– Jonathan Wakely, Commented Jun 30, 2015 at 15:22
This is a follow-on from stackoverflow.com/q/31081131/258523 . — Etan Reisner
– Etan Reisner, Commented Jun 30, 2015 at 15:25

rocky · Accepted Answer · 2015-07-09 00:09:23Z

0

The way the automake system handles this is to not use %.o: %.c but instead list the C file and all of the headers in the C file.

So for example:

main.o: main.c StarterWare_Files/test.h StarterWare_Files/add.h
    $(CC) -o $@ -MD -MP $(CPPFLAGS) $(CFLAGS) -c $^

See makedepends for a tool that will read C files and figure out the make dependencies.

answered Jul 9, 2015 at 0:09

rocky

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