嵌入式开发问题：warning: #177-D: variable “key“ was declared but never referenced

• 在 Keil MDK 中，编译项目时，出现如下警告信息

  *** Using Compiler 'V5.06 update 1 (build 61)', folder: 'D:\Keil_v5\ARM\ARMCC\Bin'
  Rebuild target 'Target 1'
  assembling startup_stm32f103xe.s...
  compiling stm32f1xx_hal.c...
  compiling stm32f1xx_hal_dma.c...
  compiling stm32f1xx_it.c...
  compiling stm32f1xx_hal_cortex.c...
  compiling stm32f1xx_hal_gpio.c...
  compiling stm32f1xx_hal_uart.c...
  compiling delay.c...
  compiling sys.c...
  compiling system_stm32f1xx.c...
  compiling main.c...
  ....\User\main.c(17): warning: #177-D: variable "key" was declared but never referenced
  uint8_t key;
  ....\User\main.c: 1 warning, 0 errors
  compiling usart.c...
  compiling stm32f1xx_hal_rcc_ex.c...
  compiling stm32f1xx_hal_gpio_ex.c...
  compiling stm32f1xx_hal_usart.c...
  compiling stm32f1xx_hal_rcc.c...
  compiling beep.c...
  compiling led.c...
  compiling exti.c...
  compiling key.c...
  linking...
  Program Size: Code=5558 RO-data=362 RW-data=28 ZI-data=1900
  FromELF: creating hex file...
  "....\Output\hal_exti.axf" - 0 Error(s), 1 Warning(s).
  Build Time Elapsed: 00:00:07

  关键错误

  ....\User\main.c(17): warning: #177-D: variable "key" was declared but never referenced
  uint8_t key;
  ....\User\main.c: 1 warning, 0 errors

问题原因

• 这个警告信息表示，在 main.c 文件中定义了一个 uint8_t key 变量，但后续代码中从未使用

处理策略

1. 如果确实不需要，删除未使用的变量

2. 如果逻辑需要，添加使用该变量的代码