passing a class variable to API function - api

Question

I want to track a global variable that I am passing into an API function. I found that one could do it using a class:
template <class T>
class MonitoredVariable
{
public:
MonitoredVariable() {}
MonitoredVariable(const T& value) : m_value(value) {}
//T operator T() const { return m_value; }
const MonitoredVariable& operator = (const T& value)
{
PlugIn::gResultOut << "value changed " << std::endl;
m_value = value;
return *this;
}
private:
T m_value;
};
The API function takes variables as
bool APIFunction(double time, bool *is_done, double *fraction_done);
The following gives me an error:
ImagePtr Im;
bool is_done;
MonitoredVariable<double*> fraction_done;
bool frameready = Im->APIFunction(2.1, is_done, fraction_done);
ERROR:
error C2664: cannot convert argument 3 from 'MonitoredVariable<double *>' to 'double *'
what would I have to change here?
thx!

Answer 1

I'm not really sure if this is what you want:
#include <iostream>
using namespace std;
template <class T>
class MonitoredVariable
{
public:
MonitoredVariable() {}
MonitoredVariable(const T& value) : m_value(value) {}
//T operator T() const { return m_value; }
const MonitoredVariable& operator = (const T& value)
{
//PlugIn::gResultOut << "value changed " << std::endl;
m_value = value.m_value;
return *this;
}
void printValue() {
std::cout << m_value;
}
T& getValue() {
return m_value;
}
private:
T m_value;
};
bool func(double firstDouble, bool *is_done, double* fraction_done) {
// do stuff
*fraction_done = firstDouble + (40.23 * 5);
*is_done = true;
return true;
}
int main()
{
bool is_done = true;
MonitoredVariable<double> fraction_done;
func(2.10, &is_done, &fraction_done.getValue());
fraction_done.printValue();
return 0;
}
So basically we have a Class called MonitoredVariable which has a variable called m_value. I'm not really sure why you wanted it to be a pointer, because we can also take the address of a normal double variable.

Answer 2

In the following it makes perhaps more sense what I want to achieve. I want to input a class variable into an API function and monitor the variable in real time. This value goes from zero to 1 every 3 ms or so. Yet I try to avoid using while loop and track it within the class with overloaded = operator.
#include "stdafx.h"
#include <iostream>
#include <thread>
#include <future>
using namespace std;
template <class T>
class MonitoredVariable
{
public:
MonitoredVariable() {}
MonitoredVariable(const T& value) : m_value(value) {}
void printValue() {
std::cout << m_value;
}
const MonitoredVariable& operator = (const T& value)
{
m_value = value.m_value;
if(m_value> 0.8) std::cout << m_value; // *THIS NEVER GETS PRINTED!!!*
return *this;
}
T& getValue() {
return m_value;
}
private:
T m_value;
};
bool func(bool *is_done, double* fraction_done) {
unsigned long c = 1;
while (*is_done)
{
*fraction_done = (double) 0.01*c;
this_thread::sleep_for(chrono::milliseconds(10));
c++;
if (*fraction_done >= 1) *is_done = false;
}
return true;
}
int main()
{
bool is_done = true;
MonitoredVariable<double> *MonitoredVariablePtr = new MonitoredVariable<double>();
std::future<bool> fu = std::async(std::launch::async,func, &is_done, &MonitoredVariablePtr->getValue());
// IF I UNCOMMENT THIS, IT PRINTS...
/*
while(is_done)
{
if(MonitoredVariablePtr->getValue() > 0.8) MonitoredVariablePtr->printValue();
}
*/
return 0;
}
Why does not the (if(m_value> 0.8) std::cout << m_value) line within the class never gets printed when the value is updated?
THX!