Roland Ver. 4.5 Technické informace stáhnout pdf (Strana 16)

6 GNU make

Thus, if we change the ﬁle insert.c and run make, make will compile that ﬁle to update

insert.o, and then link edit. If we change the ﬁle command.h and run make, make will

recompile the object ﬁles kbd.o, command.o and files.o and then link the ﬁle edit.

2.4 Variables Make Makeﬁles Simpler

In our example, we had to list all the object ﬁles twice in the rule for edit (repeated here):

edit : main.o kbd.o command.o display.o \

insert.o search.o files.o utils.o

cc -o edit main.o kbd.o command.o display.o \

insert.o search.o files.o utils.o

Such duplication is error-prone; if a new object ﬁle is added to the system, we might

add it to one list and forget the other. We can eliminate the risk and simplify the makeﬁle

by using a variable. Variables allow a text string to be deﬁned once and substituted in

multiple places later (see Chapter 6 [How to Use Variables], page 59).

It is standard practice for every makeﬁle to have a variable named objects, OBJECTS,

objs, OBJS, obj, or OBJ which is a list of all object ﬁle names. We would deﬁne such a

variable objects with a line like this in the makeﬁle:

objects = main.o kbd.o command.o display.o \

insert.o search.o files.o utils.o

Then, each place we want to put a list of the object ﬁle names, we can substitute the

variable’s value by writing ‘$(objects)’ (see Chapter 6 [How to Use Variables], page 59).

Here is how the complete simple makeﬁle looks when you use a variable for the object

ﬁles:

1 2 ... 11 12 13 14 15 16 17 18 19 20 21 ... 211 212

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Roland Ver. 4.5 Technické informace Strana 16