How to pass macro definition from “make” command line arguments (-D) to C source code?

Question

I usually pass macro definitions from \"make command line\" to a \"makefile\" using the option : -Dname=value. The definition is accessible inside the makefile.

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Answer 1

Call make command this way:

make CFLAGS=-Dvar=42

And be sure to use $(CFLAGS) in your compile command in the Makefile. As @jørgensen mentioned , putting the variable assignment after the make command will override the CFLAGS value already defined the Makefile.

Alternatively you could set -Dvar=42 in another variable than CFLAGS and then reuse this variable in CFLAGS to avoid completely overriding CFLAGS.