QNU Make Question: Append value on the command line to a predefined ?macro in the make file
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From: Jens Thoms Toerring on 28 Jan 2010 11:06 micropentium <anderswang(a)gmail.com> wrote: > Hi, > I have a c file foo.c: > int main(void) > { > #ifdef FOO > printf("FOO!\n"); > #endif > #ifdef BAR > printf("BAR!\n"); > #endif > return 0; > } > and a Makefile may be like this: > CPPFLAGS=-DFOO > a.out:foo.o > gcc -o $@ $^ > %.o:%.c > gcc -c $< ${CPPFLAGS} > if I make it and run a.out (I am on a GNU Make 3.81), the output is > FOO!. If I want to print out BAR! or FOO!BAR!, I could always append - > DBAR onto CPPFLAGS. > So, my question is: what if I want to append -DBAR on the command > line? > I tried: make CPPFLAGS+=-DBAR What you do here is set 'CPPFLAGS' to '-DBAR' in the environment first (the '=' will only matter if CPPFLAGS had a value before. Then make is started, which reads the enviroment and sets varia- bles accordingly before starting to interpret the Makefile. Whith in the Makefile you now have CPPFLAGS = -DFOO which overwrites the value from the environment. > But it will completely replace the defined CPPFLAGS in the Makefile. > Obviously, the one defined on the command line has the precedence. No, it's the other way round, a new value assigned in the Makefile will overwrite what was set previously, e.g. via the environment. > Is this doable through command line arguments to make? I'm not 100% certainr what you want to do. If you want to have '-DFOO' and '-DBAR' to be set during compilation then just change in the Makefile CPPFLAGS += -DFOO and invoke make with CPPFLAGS=-DBAR make If you want to have '-DFOO' only set if CPPFLAGS isn't set to something else do e.g. ifndef CPPFLAG CPPFLAGS=-DFOO endif in the Makefile to avoid changing an already set value of CPPFLAG. Regards, Jens -- \ Jens Thoms Toerring ___ jt(a)toerring.de \__________________________ http://toerring.de
From: micropentium on 28 Jan 2010 12:08
> > But it will completely replace the defined CPPFLAGS in the Makefile. > > Obviously, the one defined on the command line has the precedence. > > No, it's the other way round, a new value assigned in the Makefile > will overwrite what was set previously, e.g. via the environment. It depends on how you send this parameter to make If you do: CPPFLAGS=-DXX make then what you said is absolutely correct: "a new value assigned in the Makefile will overwrite what was set previously, e.g. via the environment.". But, you could always override that by add -e flag to make: CPPFLAGS=-DXX make -e, which actually replace the value of $CPPFLAGS with the one defined in env On the other hand, if you pass variable as make's arguments: make CPPFLAGS=-DXX then argument has the higher precedence than the same variable defined in the makefile. |