Makefile中:=, =, ?=和+=的含义

luckyxrq

• 直接使用 =    变量的值是最后一次被赋予的值
  

1. VIR_A = A
   
2. VIR_B = $(VIR_A)B
   
3. VIR_A = AA
   
4. 
   
5. clean:
   
6.         rm -rf $(TARGET).elf $(TARGET).dis $(TARGET).bin $(COBJS) $(SOBJS)
   
7. 
   
8.         [url=home.php?mod=space&uid=18411]@echo[/url] $(VIR_B)

复制代码

1. luckyxrq@luckyxrq:~/code/1、裸机例程/15_lcd$ make clean
   
2. rm -rf lcd.elf lcd.dis lcd.bin  obj/main.o  obj/ctype.o  obj/muldi3.o  obj/printf.o  obj/div64.o  obj/string.o  obj/vsprintf.o  obj/bsp_clk.o  obj/bsp_led.o  obj/bsp_delay.o  obj/bsp_beep.o  obj/bsp_gpio.o  obj/bsp_key.o  obj/bsp_exit.o  obj/bsp_int.o  obj/bsp_epittimer.o  obj/bsp_keyfilter.o  obj/bsp_uart.o  obj/bsp_lcd.o  obj/bsp_lcdapi.o  obj/start.o  obj/lib1funcs.o
   
3. AAB

复制代码

• 使用:=   变量的值为本次的值
  

1. VIR_A := A
   
2. VIR_B := $(VIR_A)B
   
3. VIR_A := AA
   
4. 
   
5. clean:
   
6.         rm -rf $(TARGET).elf $(TARGET).dis $(TARGET).bin $(COBJS) $(SOBJS)
   
7. 
   
8.         @echo $(VIR_B)

复制代码

1. luckyxrq@luckyxrq:~/code/1、裸机例程/15_lcd$ make clean
   
2. rm -rf lcd.elf lcd.dis lcd.bin  obj/main.o  obj/ctype.o  obj/muldi3.o  obj/printf.o  obj/div64.o  obj/string.o  obj/vsprintf.o  obj/bsp_clk.o  obj/bsp_led.o  obj/bsp_delay.o  obj/bsp_beep.o  obj/bsp_gpio.o  obj/bsp_key.o  obj/bsp_exit.o  obj/bsp_int.o  obj/bsp_epittimer.o  obj/bsp_keyfilter.o  obj/bsp_uart.o  obj/bsp_lcd.o  obj/bsp_lcdapi.o  obj/start.o  obj/lib1funcs.o
   
3. AB

复制代码

• 使用 ?=   如果之前没有赋值，则赋值，否则相当于无用语句
  

1. VIR := old_value
   
2. VIR ?= new_value
   
3. 
   
4. clean:
   
5.         rm -rf $(TARGET).elf $(TARGET).dis $(TARGET).bin $(COBJS) $(SOBJS)
   
6. 
   
7.         @echo $(VIR)

复制代码

1. luckyxrq@luckyxrq:~/code/1、裸机例程/15_lcd$ make clean
   
2. rm -rf lcd.elf lcd.dis lcd.bin  obj/main.o  obj/ctype.o  obj/muldi3.o  obj/printf.o  obj/div64.o  obj/string.o  obj/vsprintf.o  obj/bsp_clk.o  obj/bsp_led.o  obj/bsp_delay.o  obj/bsp_beep.o  obj/bsp_gpio.o  obj/bsp_key.o  obj/bsp_exit.o  obj/bsp_int.o  obj/bsp_epittimer.o  obj/bsp_keyfilter.o  obj/bsp_uart.o  obj/bsp_lcd.o  obj/bsp_lcdapi.o  obj/start.o  obj/lib1funcs.o
   
3. old_value

复制代码

• 使用 +=
  

1. VIR := old_value
   
2. VIR += $(VIR)
   
3. 
   
4. clean:
   
5.         rm -rf $(TARGET).elf $(TARGET).dis $(TARGET).bin $(COBJS) $(SOBJS)
   
6. 
   
7.         @echo $(VIR)

复制代码

1. luckyxrq@luckyxrq:~/code/1、裸机例程/15_lcd$ make clean
   
2. rm -rf lcd.elf lcd.dis lcd.bin  obj/main.o  obj/ctype.o  obj/muldi3.o  obj/printf.o  obj/div64.o  obj/string.o  obj/vsprintf.o  obj/bsp_clk.o  obj/bsp_led.o  obj/bsp_delay.o  obj/bsp_beep.o  obj/bsp_gpio.o  obj/bsp_key.o  obj/bsp_exit.o  obj/bsp_int.o  obj/bsp_epittimer.o  obj/bsp_keyfilter.o  obj/bsp_uart.o  obj/bsp_lcd.o  obj/bsp_lcdapi.o  obj/start.o  obj/lib1funcs.o
   
3. old_value old_value

复制代码

• 注意=  的统治力
  

1. VIR ?= 256
   
2. VIR = 123
   
3. 
   
4. clean:
   
5.         rm -rf $(TARGET).elf $(TARGET).dis $(TARGET).bin $(COBJS) $(SOBJS)
   
6. 
   
7.         @echo $(VIR)

复制代码

1. luckyxrq@luckyxrq:~/code/1、裸机例程/15_lcd$ make clean
   
2. rm -rf lcd.elf lcd.dis lcd.bin  obj/main.o  obj/ctype.o  obj/muldi3.o  obj/printf.o  obj/div64.o  obj/string.o  obj/vsprintf.o  obj/bsp_clk.o  obj/bsp_led.o  obj/bsp_delay.o  obj/bsp_beep.o  obj/bsp_gpio.o  obj/bsp_key.o  obj/bsp_exit.o  obj/bsp_int.o  obj/bsp_epittimer.o  obj/bsp_keyfilter.o  obj/bsp_uart.o  obj/bsp_lcd.o  obj/bsp_lcdapi.o  obj/start.o  obj/lib1funcs.o
   
3. 123

复制代码

仰望星空之云

感谢楼主分享，这次我分清了

BDWKstm32123

感谢分享~学习了

宇智波白

帮顶                          

蜗牛蜗牛

好东西顶一下