Makefile rule using the automatic variable $^ without dependencies

Question

I learnt from the GNU Make manual that the sign $^ is an automatic variable which represents the names of all the prerequisites. However I fell upon a makefile like this one:

SVR_OBJECT_FILES =      server.o\
                        server_func.o

CLT_OBJECT_FILES =      client.o

CFLAGS =                -Wall -Werror -W


CC =                    gcc

all:                   client/client server/serveur

client/client:         $(CLT_OBJECT_FILES)

server/serveur:        $(SVR_OBJECT_FILES)

client/client server/serveur:
    @mkdir -p $(dir $@)
    $(CC) $(CFLAGS) $^ -o $@

%.o: %.c
    $(CC) -c $<

clean:
    rm -f client/client server/serveur *.o

Which works fine so my question is : How can the command below can link the right object files while the $^ variable is refering no preprerequisites at all. (the rule has no prerequisites)

 $(CC) $(CFLAGS) $^ -o $@

score 5 · Accepted Answer · answered Apr 06 '13 at 13:35

$^ contains all the prerequisites of the target, not just the ones that are mentioned with the rule itself. The same file can appear as a target several times in rules with no commands:

sometarget: dependency1
…
sometarget: dependency2
        assemble -o $@ $^
…
sometarget: dependency3

The dependencies of sometarget are dependency1, dependency2 and dependency3, and when the assemble command is invoked by make sometarget, it will receive all three as arguments.

Here, $^ will contain all $(CLT_OBJECT_FILES) or $(SRV_OBJECT_FILES) depending on which target the command is executed for.

Makefile rule using the automatic variable $^ without dependencies

1 Answers1