如何借助 C++ 中的预处理器指令在行间插入语句？

Question

我正在尝试通过快速打开和关闭 LED 来对 LED 矩阵进行 PWM 编程。为了控制亮度，我想在 LED 的开和关状态之间添加额外的指令。亮度应由预处理器变量设置。 Arduino 有一个 84MHz Cortex-M3 ARM 处理器。

这是我的代码当前如何增加亮度的简化：

uint8_t volatile dummy = 0;
uint8_t i;

for (i=0;i<1<<current_layer;i++) { // every next layer has double the amount of pulses
    LED_STATE = ON; // several pulses in one go speeds up the for loop
    dummy = 0; // increases ON-time
    LED_STATE = OFF;
    LED_STATE = ON;
    dummy = 0; 
    LED_STATE = OFF;
    LED_STATE = ON;
    dummy = 0; 
    LED_STATE = OFF;
    LED_STATE = ON;
    dummy = 0;
    LED_STATE = OFF;
}

现在我希望能够像这样基于预处理器变量增加亮度：

#define BRIGHTNESS 2 
// inside loop
        LED_STATE = ON; // several pulses in one go speeds up the for loop
        #if BRIGHTNESS > 0
        dummy = 0; // increases ON-time
        #if BRIGHTNESS == 2
        dummy = 0; // increases ON-time even more
        #endif
        #endif
        LED_STATE = OFF;
        LED_STATE = ON;
        #if BRIGHTNESS > 0
        dummy = 0;
        #if BRIGHTNESS == 2
        dummy = 0;
        #endif
        #endif
        LED_STATE = OFF;
        LED_STATE = ON;
        #if BRIGHTNESS > 0
        dummy = 0;
        #if BRIGHTNESS == 2
        dummy = 0;
        #endif
        #endif
        LED_STATE = OFF;
        LED_STATE = ON;
        #if BRIGHTNESS > 0
        dummy = 0;
        #if BRIGHTNESS == 2
        dummy = 0;
        #endif
        #endif
        LED_STATE = OFF;

如您所见，这使得代码非常难读。我想定义一个预处理器宏，根据 BRIGHTNESS.

的值添加这些虚拟语句

代码应该是这样的：

#define BRIGHTNESS 2 
#define B1 ... // adds dummy=0; when BRIGHTNESS > 0 or else nothing at all
#define B2 ...
#define B3 ...
#define B4 ...
// inside loop
        LED_STATE = ON;
        B1 B2 B3 B4 // adds a number of dummy statements based on the value of BRIGHTNESS
        LED_STATE = OFF;
        LED_STATE = ON;
        B1 B2 B3 B4
        LED_STATE = OFF;
        LED_STATE = ON;
        B1 B2 B3 B4
        LED_STATE = OFF;
        LED_STATE = ON;
        B1 B2 B3 B4
        LED_STATE = OFF;

更好的是基于变量插入这些语句的函数：

#define ADD_DUMMIES ...
// inside loop
        LED_STATE = ON;
        ADD_DUMMIES(BRIGHNESS)
        LED_STATE = OFF;

我将如何定义预处理器宏，以便它们根据 BRIGHTNESS 的值插入虚拟语句？

Answer 1

这是如何在预处理器的帮助下添加 dummy = 0; 语句：

#define BRIGHTNESS 2
#define _GETFOO(n) _FOO ## n
#define ADD_DUMMIES(n) _GETFOO(n) ()

#define _FOO0()
#define _FOO1() dummy = 0;
#define _FOO2() dummy = 0; dummy = 0;
#define _FOO3() dummy = 0; dummy = 0; dummy = 0;
#define _FOO4() dummy = 0; dummy = 0; dummy = 0; dummy = 0;

uint8_t volatile dummy = 0;
// inside loop
        LED_STATE = ON;
        ADD_DUMMIES(BRIGHTNESS)
        LED_STATE = OFF;
        LED_STATE = ON;
        ADD_DUMMIES(BRIGHTNESS)
        LED_STATE = OFF;
        LED_STATE = ON;
        ADD_DUMMIES(BRIGHTNESS)
        LED_STATE = OFF;
        LED_STATE = ON;
        ADD_DUMMIES(BRIGHTNESS)
        LED_STATE = OFF;

只要在边界内，编译器就会根据 BRIGHTNESS 的值在行之间插入相同的存储指令。

如何借助 C++ 中的预处理器指令在行间插入语句？

How to insert a statement inbetween lines with the help of preprocessor directives in C++?

c

macros

inline

preprocessor-directive

dummy-variable