gnu make : how to make conditional cflags

问题

I started a simple makefile for my project (MS-windows target, MinGW) with the following :

CFLAGS = -g -O0 -Wall -std=c99

CC =    gcc
CPP =   g++
LIBS =

PBDUMPER = pbdumper.exe

all: $(PBDUMPER)

$(PBDUMPER): pbdumper.c
    $(CC) $(CFLAGS) -o $@ $< $(LIBS)

clean:
    rm -f $(PBDUMPER)

.PHONY: clean

Now I would like to choose between release and debug compilation. I have changed the variable definitions and implicit rule for debug :

CFLAGS_COMMON = -std=c99
CFLAGS_DEBUG = -g -O0 -Wall
CFLAGS_RELEASE = -O2 -Wall
...
$(PBDUMPER): pbdumper.c
    $(CC) $(CFLAGS_COMMON) $(CFLAGS_DEBUG) -o $@ $< $(LIBS)

But for release I would have to change the implicit rule to use the CFLAGS_RELEASE which is I suppose the wrong way to do. I have looked at the Gnu Make manual in the "implicit rules" and "automatic variables" sections but I did not found a better way.

Could you show me the correct way, by either conditionally defining the CFLAGS, or maybe using a "if" in the implicit rules based on the flavour selected for compilation ? Or maybe another method.

回答1:

For the sake of archiving the solution and not keeping a question unanswered, here is the final word : following Maxim's suggestion, I have reworked my Makefile as :


#debug is default, for another flavor : make BUILD=release
BUILD := debug

cflags.common := -std=c99
cflags.debug := -g -O0 -Wall
cflags.release := -O2 -Wall
CFLAGS := ${cflags.${BUILD}} ${cflags.common}
LIBS =

CC =    gcc
CPP =   g++

#executable
PBDUMPER = pbdumper.exe

all: $(PBDUMPER)

$(PBDUMPER): pbdumper.c
    $(CC) $(CFLAGS) -o $@ $< $(LIBS)

clean:
    rm -f $(PBDUMPER)

.PHONY: clean all

回答2:

The easiest way would be a simple comment/uncomment solution:

CFLAGS = -std=c99
# Release
# CFLAGS += -O2 -Wall
# Debug
CFLAGS += -g -O0 -Wall

This is how automake does this type of configuration. You could also use a make conditional around these lines:

ifeq ($(build),release)
    CFLAGS += -O2 -Wall
else
    CFLAGS += -g -O0 -Wall
endif

In general, be careful with such schemes because you absolutely have to clean out old object files on release. Two-tree builds with autoconf and automake (or a simple hand-rolled configure) are more reliable, even though a little harder to set up.

来源：https://stackoverflow.com/questions/8035394/gnu-make-how-to-make-conditional-cflags

标签

mingw

gnu-make