Roland Ver. 4.5 Informações Técnicas descarregar pdf (Página 29)

Chapter 3: Writing Makeﬁles 19

$*, etc. during the second expansion and they will have their expected values, just as in

the recipe. All you have to do is defer the expansion by escaping the $. Also, secondary

expansion occurs for both explicit and implicit (pattern) rules. Knowing this, the possible

uses for this feature increase dramatically. For example:

.SECONDEXPANSION:

main_OBJS := main.o try.o test.o

lib_OBJS := lib.o api.o

main lib: $$($$@_OBJS)

Here, after the initial expansion the prerequisites of both the main and lib targets will

be $($@_OBJS). During the secondary expansion, the $@ variable is set to the name of the

target and so the expansion for the main target will yield $(main_OBJS), or main.o try.o

test.o, while the secondary expansion for the lib target will yield $(lib_OBJS), or lib.o

api.o.

You can also mix in functions here, as long as they are properly escaped:

main_SRCS := main.c try.c test.c

lib_SRCS := lib.c api.c

.SECONDEXPANSION:

main lib: $$(patsubst %.c,%.o,$$($$@_SRCS))

This version allows users to specify source ﬁles rather than object ﬁles, but gives the

same resulting prerequisites list as the previous example.

Evaluation of automatic variables during the secondary expansion phase, especially of

the target name variable $$@, behaves similarly to evaluation within recipes. However, there

are some subtle diﬀerences and “corner cases” which come into play for the diﬀerent types

of rule deﬁnitions that make understands. The subtleties of using the diﬀerent automatic

variables are described below.

Secondary Expansion of Explicit Rules

During the secondary expansion of explicit rules, $$@ and $$% evaluate, respectively, to the

ﬁle name of the target and, when the target is an archive member, the target member name.

The $$< variable evaluates to the ﬁrst prerequisite in the ﬁrst rule for this target. $$^ and

$$+ evaluate to the list of all prerequisites of rules that have already appeared for the same

target ($$+ with repetitions and $$^ without). The following example will help illustrate

these behaviors:

.SECONDEXPANSION:

foo: foo.1 bar.1 $$< $$^ $$+ # line #1

foo: foo.2 bar.2 $$< $$^ $$+ # line #2

foo: foo.3 bar.3 $$< $$^ $$+ # line #3

In the ﬁrst prerequisite list, all three variables ($$<, $$^, and $$+) expand to the empty

string. In the second, they will have values foo.1, foo.1 bar.1, and foo.1 bar.1 respec-

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Roland Ver. 4.5 Informações Técnicas Página 29