The attributes of my child class are lazily initialized - c++

Question

I have created a parent class in C++ and one child class which I have two attributes: _trigger and _echo. In order to use my child class I declare it and I assign its address to a pointer of the parent class. Hence, I use the methods of my parent class.
My problem: When I use the method cyclePulse without parameters (int trigger, int echo) and the attributes from my class (_trigger and _echo), the method does not work properly. I guess it is because the attributes _trigger and _echo are lazily initialized, or because I am not using new keyword when I am creating my object.
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();
};
Here is the implementation of HCSR04.cpp. Edited: I forgot the constructors.
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;
}
I am using the class like this:
HCSR04 deviceUltrasonic;
ISensor * sensorUltrasonic = &deviceUltrasonic;
char* readRequestArray = sensorUltrasonic->readRequest();

Answer 1

Giving my previous comment as a possible answer here, because I assume that the uninitialized variables are causing your fault here:
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;
}