Roland Ver. 4.5 Technical Information PDF herunterladen (Seite 82)

72 GNU make

pattern ... : variable-assignment

where pattern is a %-pattern. As with target-speciﬁc variable values, multiple pattern

values create a pattern-speciﬁc variable value for each pattern individually. The variable-

assignment can be any valid form of assignment. Any command line variable setting will

take precedence, unless override is speciﬁed.

For example:

%.o : CFLAGS = -O

will assign CFLAGS the value of ‘-O’ for all targets matching the pattern %.o.

If a target matches more than one pattern, the matching pattern-speciﬁc variables with

longer stems are interpreted ﬁrst. This results in more speciﬁc variables taking precedence

over the more generic ones, for example:

%.o: %.c

$(CC) -c $(CFLAGS) $(CPPFLAGS) $< -o $@

lib/%.o: CFLAGS := -fPIC -g

%.o: CFLAGS := -g

all: foo.o lib/bar.o

In this example the ﬁrst deﬁnition of the CFLAGS variable will be used to update

lib/bar.o even though the second one also applies to this target. Pattern-speciﬁc

variables which result in the same stem length are considered in the order in which they

were deﬁned in the makeﬁle.

Pattern-speciﬁc variables are searched after any target-speciﬁc variables deﬁned explic-

itly for that target, and before target-speciﬁc variables deﬁned for the parent target.

6.13 Suppressing Inheritance

As described in previous sections, make variables are inherited by prerequisites. This capa-

bility allows you to modify the behavior of a prerequisite based on which targets caused it

to be rebuilt. For example, you might set a target-speciﬁc variable on a debug target, then

running ‘make debug’ will cause that variable to be inherited by all prerequisites of debug,

while just running ‘make all’ (for example) would not have that assignment.

Sometimes, however, you may not want a variable to be inherited. For these situations,

make provides the private modiﬁer. Although this modiﬁer can be used with any variable

assignment, it makes the most sense with target- and pattern-speciﬁc variables. Any variable

marked private will be visible to its local target but will not be inherited by prerequisites

of that target. A global variable marked private will be visible in the global scope but will

not be inherited by any target, and hence will not be visible in any recipe.

As an example, consider this makeﬁle:

EXTRA_CFLAGS =

prog: private EXTRA_CFLAGS = -L/usr/local/lib

prog: a.o b.o

Due to the private modiﬁer, a.o and b.o will not inherit the EXTRA_CFLAGS variable

assignment from the prog target.

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Roland Ver. 4.5 Technical Information Seite 82