Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 40)

30 GNU make

By declaring the sub-directories as .PHONY targets (you must do this as the sub-directory

obviously always exists; otherwise it won’t be built) you can remove these problems:

SUBDIRS = foo bar baz

.PHONY: subdirs $(SUBDIRS)

subdirs: $(SUBDIRS)

$(SUBDIRS):

$(MAKE) -C $@

foo: baz

Here we’ve also declared that the foo sub-directory cannot be built until after the baz

sub-directory is complete; this kind of relationship declaration is particularly important

when attempting parallel builds.

The implicit rule search (see Chapter 10 [Implicit Rules], page 111) is skipped for .PHONY

targets. This is why declaring a target as .PHONY is good for performance, even if you are

not worried about the actual ﬁle existing.

A phony target should not be a prerequisite of a real target ﬁle; if it is, its recipe will

be run every time make goes to update that ﬁle. As long as a phony target is never a

prerequisite of a real target, the phony target recipe will be executed only when the phony

target is a speciﬁed goal (see Section 9.2 [Arguments to Specify the Goals], page 99).

Phony targets can have prerequisites. When one directory contains multiple programs,

it is most convenient to describe all of the programs in one makeﬁle ./Makefile. Since the

target remade by default will be the ﬁrst one in the makeﬁle, it is common to make this

a phony target named ‘all’ and give it, as prerequisites, all the individual programs. For

example:

all : prog1 prog2 prog3

.PHONY : all

prog1 : prog1.o utils.o

cc -o prog1 prog1.o utils.o

prog2 : prog2.o

cc -o prog2 prog2.o

prog3 : prog3.o sort.o utils.o

cc -o prog3 prog3.o sort.o utils.o

Now you can say just ‘make’ to remake all three programs, or specify as arguments the ones

to remake (as in ‘make prog1 prog3’). Phoniness is not inherited: the prerequisites of a

phony target are not themselves phony, unless explicitly declared to be so.

When one phony target is a prerequisite of another, it serves as a subroutine of the other.

For example, here ‘make cleanall’ will delete the object ﬁles, the diﬀerence ﬁles, and the

ﬁle program:

.PHONY: cleanall cleanobj cleandiff

1 2 ... 35 36 37 38 39 40 41 42 43 44 45 ... 211 212

Sem comentários

Roland Ver. 4.5 Informações Técnicas Página 40