What does this do in makefiles?

Question

Here is the line that bothers me:

CFLAGS+=-DCONTIKI_VERSION_THINKSQUARE=1

There are so many signs one after another (+=-) that totally confuses me :) I know that += is append operator, but the right side is unknown for me. Thank you in advance.

See this http://stackoverflow.com/q/448910/2968959 – Saurabh Meshram Jul 15 '15 at 10:17 — Saurabh Meshram, Jul 15 '15 at 10:17

score 1 · Accepted Answer · answered Jul 15 '15 at 07:51

1

The whole right side of += is interpreted as a string that is appended to the makefile variable CFLAGS. Say, your makefile is:

CFLAGS:=VAL1
CFLAGS+=-DCONTIKI_VERSION_THINKSQUARE=1

all:
    @echo $(CFLAGS)

make all will output:

VAL1 -DCONTIKI_VERSION_THINKSQUARE=1

answered Jul 15 '15 at 07:51

Eugeniu Rosca

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But isn't -D some kind of directive like #define CONTIKI_VERSION_THINKSQUARE 1 – Radoslaw Krasimirow Jul 15 '15 at 08:04
@Radoslaw Krasimirow: Make doesn't care what is `-D`. You asked what happens in makefile language. What happens if you pass the `CFLAGS` to `gcc` is a different issue altogether! – Eugeniu Rosca Jul 15 '15 at 08:07

What does this do in makefiles?

1 Answers1