On: Makefiles – Best Practices

[aaaaaaaaaaab]

    CFLAGS := ${CFLAGS}
    CFLAGS += -ansi -std=99

What's the point of the first line? Why not just:

    CFLAGS += -ansi -std=99

[jgrahamc → aaaaaaaaaaab]

If turns CFLAGS from a recursive variable to a simple one. Hence it will not be re-expanded every time it is used. This is a speed optimization.

    $ cat Makefile
    CFLAGS = -Wall
    $(info $(flavor CFLAGS))
    CFLAGS := $(CFLAGS)
    $(info $(flavor CFLAGS))
    $ make
    recursive
    simple

But TFA says that the author is using := to prevent a recursive definition. It's unclear why the author doesn't just += without doing = or := (unless they want the recursive to simple conversion I talk about above). My guess is the author sligthly misunderstood the handling of the environment inside a Makefile.

[smitherfield → aaaaaaaaaaab]

Speaking of, why both -ansi and -std=99 [sic[1]]?

[1] should be -std=c99

[danyspin97 → smitherfield]

I've used these comments[1] as source for writing the CFLAGS. Did I misunderstood?

[1] https://stackoverflow.com/a/2193647

[dewhelmed → aaaaaaaaaaab]

Because CFLAGS may not be set in the environment, resulting in concatenation to an undefined variable error.

[jgrahamc → dewhelmed]

No such error occurs.

    $ cat Makefile
    FOO += foo

    all: ; @echo $(FOO)
    $ make
    foo

[dewhelmed → jgrahamc]

My bad, I felt like I've seen that error pop up before in my Makefiles, but I should have double-checked before commenting.

[jschwartzi → dewhelmed]

There's no such thing as an undefined variable in Make. The variable expands to text. Variables which are not defined by definition expand to no text.

[dewhelmed → jschwartzi]

My bad, I felt like I've seen that error pop up before in my Makefiles, but I should have double-checked before commenting.

[pooya13 → aaaaaaaaaaab]

My guess is that the left hand side is a make variable while the right hand side is an environment variable. However the make manual says “Every environment variable that make sees when it starts up is transformed into a make variable with the same name and value.“ so maybe it’s not necessary?...

[pooya13 → pooya13]

This reminds me why I stopped visiting HN. People down vote you for trying to help! Screw whoever asshole that downvoted me even though I prefixed my answer with “My GUESS is...”.