C++ Static Function/Namespace issue - c++

Question

I am having issues with some code. In the CrossingSensor::loop() function, there is a line with: sonar.ping_timer(readSensor);.
I can call that fine, but in that function I can't access the status variable. What am I missing?
Error: error: 'status' was not declared in this scope status = on;
/*
Name
*/
#ifndef CrossingSensor_h
#define CrossingSensor_h
#include "Arduino.h"
class CrossingSensor
{
enum Status {off, on};
public:
CrossingSensor();
void init();
void loop();
void start();
void stop();
Status status;
private:
unsigned long _startMillis;
};
#endif
/*
NLE
*/
#include "Arduino.h"
#include "CrossingSensor.h"
#include <NewPing.h>
NewPing sonar(2,3,6);//trigger, echo, max distance
unsigned int pingSpeed = 500;// 50ms would be 20 times a second
unsigned long pingTimer;// Holds the next ping time
CrossingSensor::CrossingSensor()
{
Serial.println("CrossingSensor: Init");
//init();
}
void CrossingSensor::init()
{
Serial.println("CrossingSensor: Init/Attach/Reset");
pingTimer = millis();
}
void readSensor()
{
if (sonar.check_timer())
{
int cm = sonar.ping_result / US_ROUNDTRIP_CM;
if(cm > 0 && cm < 10)
{
//status = on;
}
else
{
//status = off;
}
}
}
void CrossingSensor::loop()
{
if (millis() >= pingTimer)
{
pingTimer += pingSpeed;
sonar.ping_timer(readSensor);
}
}
void CrossingSensor::start()
{
if(status == off)
{
Serial.println("CrossingSensor: Turning Sensor On");
status = on;
}
}
void CrossingSensor::stop()
{
if(status == on)
{
Serial.println("CrossingSensor: Turning Sensor Off");
status = off;
}
}

Answer 1

You never declared the function readSensor() as a part of CrossingSensor. Since it isn't a member function, it has no access to status.
All you should have to do is declare the function as a member of CrossingSensor or pass it a CrossingSensor object.
You would also need to change the .cpp file to reflect that change. The declaration for each would look like the following:
class CrossingSensor
{
enum Status {off, on};
public:
CrossingSensor();
void init();
void readSensor();
void loop();
void start();
void stop();
Status status;
private:
unsigned long _startMillis;
};
#endif
This is your method declaration:
void CrossingSensor::readSensor()
{
// your code here
}
This makes readSensor a part of CrossingSensor as well as the other way around.

Answer 2

The readSensor() function isn't part of CrossingSensor so it can't see CrossingSensor's status.
Make it part of Crossingsensor by declaring it there in your header file, and then define it as void CrossingSensor::readSensor(), in your code, and not as void readSensor().
Also, I don't know what sonar.ping_timer() takes as an argument, but I doubt it is readSensor. You will have to find another way of passing status to sonar.ping_timer(), if that is what you intended to do.