可变变量以更改Makefile中目标的先决条件

Question

我希望使用'MY_TYPE'来切换目标'top'的先决条件。

基于MY_TYPE，我可以选择所需的先决条件

例如，对于

MY_TYPE = FOO，我希望以$（BUILD）$（TARGETS）$（X_LOCALS）作为页首的先决条件

MY_TYPE = BAR，我希望以$（BUILD）$（TARGETS）$（Y_LOCALS）作为页首的先决条件

如何实现？

下面是一个简单的代码段。

BUILD = build
TARGETS = targets
XLOCALS = xlocals
YLOCALS = ylocals

# can be FOO or BAR
MY_TYPE ?= FOO

$(BUILD):
    printf "\t Doing Build\n"

$(TARGETS): 
    printf "\t Doing target\n"

$(XLOCALS):
    printf "\t my local build for X \n"

$(YLOCALS):
    printf "\t my local build for Y \n"


# based on MY_TYPE Can I select the pre-requisites required
# For example, for 
# MY_TYPE=FOO , I wish to have  $(BUILD) $(TARGETS) $(X_LOCALS) as pre-requisites for 'top' target
# MY_TYPE=BAR , I wish to have  $(BUILD) $(TARGETS) $(Y_LOCALS) as pre-requisites for 'top' target
# How can I achieve it .

top: $(BUILD) $(TARGETS) $(XLOCALS)
    printf "\t doing top\n"

很高兴考虑一下。

Answer 1

再简单不过了，只需使用conditionals：

ifeq ($(MY_TYPE),FOO)
top: $(X_LOCALS)
endif

ifeq ($(MY_TYPE),BAR)
top: $(Y_LOCALS)
endif

top: $(BUILD) $(TARGETS)
        @echo prereqs are $^

EDIT：完整示例：

BUILD = build
TARGETS = targets
XLOCALS = xlocals
YLOCALS = ylocals

# can be FOO or BAR                                                                                                       
MY_TYPE ?= BAR

$(BUILD):
    printf "\t Doing Build\n"

$(TARGETS):
    printf "\t Doing target\n"

$(XLOCALS):
    printf "\t my local build for X \n"

$(YLOCALS):
    printf "\t my local build for Y \n"

ifeq ($(MY_TYPE),FOO)
top: $(XLOCALS)
endif

ifeq ($(MY_TYPE),BAR)
top: $(YLOCALS)
endif

top: $(BUILD) $(TARGETS)
    printf "\t doing top\n"