Question

我用C ++创建了一个父类，并创建了一个具有两个属性的子类：_trigger和_echo。为了使用我的子类，我对其进行了声明，并将其地址分配给父类的指针。因此，我使用父类的方法。

我的问题：当我使用没有参数（cyclePulse）和类的属性（int trigger, int echo和_trigger）的方法_echo时，该方法不起作用正确地。我猜这是因为_trigger和_echo属性是延迟初始化的，或者是因为我在创建对象时没有使用new关键字。

class ISensor {
...
public:
    ISensor();
    virtual ~ISensor();
    ...
    virtual int connect() = 0;
    virtual char * readRequest() = 0;
    virtual int disconnect() = 0;
};

class HCSR04: public ISensor {
private:
    int _trigger;
    int _echo;
public:
    HCSR04();
    HCSR04(int trigger, int echo);
    ...
    int connect();
    char * readRequest();
    uint64_t cyclePulse(int trigger, int echo);
    float distanceCentimeters();
};

这是HCSR04.cpp的实现。编辑：我忘记了构造函数。

HCSR04::HCSR04() {
    _echo = RPI_V2_GPIO_P1_13;
    _trigger = RPI_V2_GPIO_P1_15;
}
HCSR04::HCSR04(int trigger, int echo) {
    _echo = echo;
    _trigger = trigger;
}    
char * HCSR04::readRequest() {
    float preCent = distanceCentimeters();
    char* buf = new char[20];
    sprintf(buf, "%.10f", preCent);
    return buf;
}
float HCSR04::distanceCentimeters() {
    return (float) cyclePulse(_trigger, _echo) / 55.5;
}
uint64_t HCSR04::cyclePulse(int trigger, int echo) {
    uint64_t width, begin, start, end;
    int max = 80, check;

    begin = bcm2835_st_read();

    // Emit pulse for 10 microseconds
    bcm2835_gpio_write(_trigger, HIGH); // Set trigger state HIGH
    bcm2835_delayMicroseconds(10);  // Wait 10 microseconds
    bcm2835_gpio_write(_trigger, LOW);  // Set trigger state LOW

    while (bcm2835_gpio_lev(_echo) == LOW && check < max) {
        start = bcm2835_st_read();
        check = (int) begin - start;
    }
    while (bcm2835_gpio_lev(_echo) == HIGH) {
        bcm2835_delayMicroseconds(1);
    }
    end = bcm2835_st_read();

    width = end - start;

    return width;
}

我正在使用这样的课程：

HCSR04 deviceUltrasonic;
ISensor * sensorUltrasonic = &deviceUltrasonic;
char* readRequestArray = sensorUltrasonic->readRequest();

Answer 1

在这里给出我以前的评论作为可能的答案，因为我认为未初始化的变量正在引起您的错误：

uint64_t HCSR04::cyclePulse(int trigger, int echo) {
    uint64_t width, begin, start, end;
    int max = 80, check = 0;  // <<< init check to 0. 
                              // Btw: size_t or any other unsigned type matches
                              // better the purpose of what you want to achieve.

    begin = bcm2835_st_read();

    // begin is not used afterwards. Did you mean to initialize "start" here?
    start = begin;

    // Emit pulse for 10 microseconds
    bcm2835_gpio_write(_trigger, HIGH); // Set trigger state HIGH
    bcm2835_delayMicroseconds(10);  // Wait 10 microseconds
    bcm2835_gpio_write(_trigger, LOW);  // Set trigger state LOW

    while (bcm2835_gpio_lev(_echo) == LOW && check < max) {
        start = bcm2835_st_read();
        check = (int) begin - start;
    }
    while (bcm2835_gpio_lev(_echo) == HIGH) {
        bcm2835_delayMicroseconds(1);
    }
    end = bcm2835_st_read();

    width = end - start;

    return width;
}

我的子类别的属性是延迟初始化的

1 个答案: