defining default values in makefile

Question

My makefile has line like this

   CFLAGS = -c -g -D OPT1 -D OPT2

I want to pass this arguments through command line like this

 make ARG1= OPT1 ARG2 =OPT2    

If I dont pass these arguments through command line I want makefile to use take default values defined in makefile. How do I do that ?

Solution

Just do something like this in the makefile:

OPT1 = MY_OPT_1 # defaults
OPT2 = MY_OPT_2

CFLAGS = -c -g -D $(OPT1) -D $(OPT2)

Then on the command line:

$ make -e OPT1=SOME_OTHER_OPT1 OPT2=SOME_OTHER_OPT2

When you specify falues for OPT1 and/or OPT2 on the command line these will override the default values in the makefile.

Note that you probably want the -e option with make in most cases to force everything to be re-built with the new OPT1, OPT2 values.

Comments

[Paul R]

possible duplicate of Passing additional variables from command line to make

[Ian Hickman]

Use #ifdef OPT2 #endif in your c/cpp file