Arduino 中的 C++ 结构多态性

Question

我有一个名为 Quadruped_Robot 的类，它有四个结构，fRight、fLeft、bRight 和 bLeft 继承自基础结构 Leg。在 Arduino 中，我尝试通过循环驱动 8 个伺服电机，这四个结构保存伺服驱动器 channel 值。我创建了一个指向这四个结构的指针数组，以便函数 actuateLeg 可以将 PWM 信号发送到在运行时确定的适当 channel 。然而，没有伺服系统响应，并且在检查 myLeg->channels[0] 和 myLeg->channels[1] 给出的值时，它们报告的值是在数以千计的范围内，包括正数和负数。但是，值应介于 0 和 7 之间。为什么当我尝试使用 -> 运算符访问它们时 channel 值不正确？

#include <Wire.h>
#include <Adafruit_PWMServoDriver.h>

//default address
Adafruit_PWMServoDriver pwm = Adafruit_PWMServoDriver();

class Quadruped_Robot{

  private:
  //minimum and maximum pulse length count
  //valid range: [0,4096]
  //0   degrees:    200
  //60  degrees:    360
  //90  degrees:    510
  //180 degrees:    915
  size_t SERVOMIN= 200;
  size_t SERVOMAX= 915;

  //phase shift between upper and lower leg actuation in milliseconds
  size_t OFFSET= 1000;

  //pulse length to servo motors
  size_t PULSE_LENGTH= 100;

  struct Leg{
    int channels[2];
    bool started;
    virtual void foo()=0;
  };

  struct fRight:Leg{
    //channel numbers on the PWM/Servo driver for the front right leg
    //0= upper leg
    //1= lower leg
    int channels[2]= {0, 1};
    bool started= false;
    virtual void foo(){}
  };

  struct fLeft:Leg{
    //channel numbers on the PWM/Servo driver for the front left leg
    //2= upper leg
    //3= lower leg
    int channels[2]= {2, 3};
    bool started= false;
    virtual void foo(){}
  };

  struct bRight:Leg{
    //channel numbers on the PWM/Servo driver for the back right leg
    //4= upper leg
    //5= lower leg
    int channels[2]= {4, 5};
    bool started= false;
    virtual void foo(){}
  };

  struct bLeft:Leg{
    //channel numbers on the PWM/Servo driver for the back left leg
    //6= upper leg
    //7= lower leg
    int channels[2]= {6, 7};
    bool started= false;
    virtual void foo(){}
  };

  //bool value indicating whether the servos have begun moving
  bool started= false;

  //holds the previous timestamp
  unsigned long prevTime;

  public:

  Leg* myLegs[4]= {new fRight, new fLeft, new bRight, new bLeft};

  void actuateLeg(size_t leg){  
    prevTime= millis();
    Leg *myLeg= myLegs[leg];
    size_t PWM= SERVOMIN;

    //Actuate upper leg and wait until the phase shift time has elapsed to actuate the lower leg
    while(millis()-prevTime < OFFSET){
      pwm.setPWM(myLeg->channels[0], 0, PWM );
      Serial.println(myLeg->channels[0]);
    }
    prevTime= millis();

    //Actuate lower leg and wait until the phase shift time has elapsed to actuate the upper leg again
    while(millis()-prevTime < OFFSET){
      pwm.setPWM(myLeg->channels[1], 0, PWM );
      Serial.println(myLeg->channels[1]);
    }
    prevTime= millis();
    PWM= SERVOMAX;

    //Actuate upper leg and wait until the phase shift time has elapsed to actuate the lower leg again
    while(millis()-prevTime < OFFSET){
      pwm.setPWM(myLeg->channels[0], 0, PWM );
      Serial.println(myLeg->channels[0]);
    }
    prevTime= millis();

    while(millis()-prevTime < OFFSET){
      pwm.setPWM(myLeg->channels[1], 0, PWM );
      Serial.println(myLeg->channels[1]);
    }
    delete myLeg;
  }

  void walk(){
    actuateLeg(0);
    actuateLeg(2);
    actuateLeg(1);
    actuateLeg(3);
  }

};

//Create a Quadruped_Robot object
Quadruped_Robot myQuadruped;

void setup() {
  //Begin serial communication at 9600 bps
  Serial.begin(9600);

  //MG996R servo runs at 50 Hz
  pwm.setPWMFreq(50);
  pwm.begin();

}

void loop() {
  myQuadruped.walk();

}

Answer 1

您的每个腿类(fRight、fLeft、bRight、bLeft)都会创建两个变量:

int channels[2]= {2, 3};
bool started= false;

...这会创建一个无法通过 Leg 指针访问的不同拷贝。

您需要更改为类似以下内容以确保您在基本结构 Leg 中设置值。

struct fRight :  Leg
{
    fRight() {
        started = false;
        channels[0] = 0;
        channels[1] = 1;
    }
    virtual void foo() {}
};

虽然您甚至可能不需要这些单独的类(取决于您的纯虚拟 foo() 需要做什么)。如果您要将 Leg 更改为:

struct Leg
{
    Leg(int channel1, int channel2) :
        started {false}
    {
        channels[0] = channel1;
        channels[1] = channel1;
    }

    int channels[2];
    bool started;
    //virtual void foo() = 0;
};

...你可以实例化:

Leg* myLegs[4] = { new Leg{0,1}, new Leg{2,3}, new Leg{4,5}, new Leg{6,7} }