A strange make rule

Hello everyone,


Here is a sample make file.

SRC=foo.c
PROC=$(SRC:%.c=%.o)
TARGET=$(PROC:%.o=$(TARGET_DIR)/%.o)

I know the first two lines mean compile *.c defined in SRC to *.o. But what does the 3rd line mean? Convert *.o generated by PROC to *.o? I am confused that why convert *.o to *.o itself?


thanks in advance,
George