---关于Makefile标签两个冒号的问题

bzhao

#$(OBJS):%.o:%.cpp
%.o:%.cpp

这里我用这两行都是可以的，请问用两个冒号的行作用是？

------------
###// Makefile
# make gst example

$(info $(CXX))

FLAGS = -g
OBJS = main.o
TARGETS = gstest

INCLUDEPATH = $(shell pkg-config --cflags glib-2.0 gstreamer-1.0 )
LIBS = $(shell pkg-config --libs glib-2.0 gstreamer-1.0)

all:$(TARGETS)

$(TARGETS):$(OBJS)
$(CXX) $(FLAGS) $< -o $@ $(LIBS)

#$(OBJS):%.o:%.cpp
%.o:%.cpp
$(CXX) $(FLAGS) -c $< -o $@ $(INCLUDEPATH)
clean:
rm -rf $(TARGETS) $(OBJS)