12. Writing rules - static mode

Static mode makes it easier to define multi-objective rules , It can make our rules more flexible and flexible .
Let's take a look at grammar first ：

<targets ...>: <target-pattern>: <prereq-patterns ...>
<commands>
....

targets Defines a series of object files , There can be wildcards . It's a collection of goals ;
target-parrtern It's pointed out targets The pattern of , That is, the target set pattern of ;
prereq-parrterns It's a dependency pattern of goals , It's right target-parrtern The formed pattern defines the dependency target again .

 Let's take an example .
 If our <target-parrtern> Defined as “%.o”, It means our <target> All of the collections are based on “.o” At the end of the ,
 And if our <prereq-parrterns> Defined as “%.c”, It means right <target-parrtern> The formed target set is defined twice ,

 The calculation method is :
 take <target-parrtern> In the pattern “%”（ That is to remove [.o] This ending ）, And add [.c] This ending , The formation of a new collection .

therefore , our “ Target mode ” or “ Dependency patterns ” There should be “%” This character , If your file name contains “%” So you can use the backslash “\” Transference , To mark the real “%” character .

Take an example ：

objects = foo.o bar.o
all: $(objects)
$(objects): %.o: %.c
$(CC) -c $(CFLAGS) $< -o [email protected]

 It points out our goal from $object  In order to get ,“%.o” Make it clear that you want all of them to “.o” End goal , That is to say “foo.o bar.o”,
 That's the variable $object  The pattern of sets ;

 And dependency patterns “%.c” Then take the mode “%.o” Of “%”, That is to say “foo bar”, And add “.c” The suffix ,
 therefore , Our dependency goal is “foo.c bar.c”.

 And in the order “$<” and “[email protected]” It's the automation variable ,
“$<” Represents all dependent target sets （ That is to say “foo.c bar.c”）,
“[email protected]” Represents the target set （ That is to say “foo.o bar.o”）.

 therefore , The expanded rules above are equivalent to the rules below ：

foo.o : foo.c
$(CC) -c $(CFLAGS) foo.c -o foo.o
bar.o : bar.c
$(CC) -c $(CFLAGS) bar.c -o bar.o

Just imagine , If our “%.o” There are hundreds , We just need to use this very simple one “ Static mode rules ” You can write a bunch of rules , It's so efficient .“ Static mode rules ” The usage of is very flexible , If it works well , That would be a very powerful function .