Makefile的call函数

写了个例子来研究Makefile的call函数：

#define a multiline variable
define target 
	echo $@
	echo $@
endef

#define the target which is the first target, so default target
all:
	$(call target,all)

#define the second target, we must explicitly make it
clean:
	$(call target,clean)	

#declare that all and clean are phony targets
.PHONY: all clean

执行make或make all的结果是：

echo all
all
echo all
all

执行make clean的结果是：

echo clean
clean
echo clean	
clean

其实源代码可以这么写的：

#define a multiline variable
define target 
	echo $@
	echo $@
endef

#define the target which is the first target, so default target
all:
	$(call target)

#define the second target, we must explicitly make it
clean:
	$(call target)	

#declare that all and clean are phony targets
.PHONY: all clean

结果跟上面一样。

小结：Makefile中的第一个目标是最终目标，是make默认执行的目标，call函数会以此调用多行变量的每一个（此处是make命令，所以会被执行了）。然后$@自动化变量在make执行是会被赋值为当前的目标。