Given that all else is equal, and there are no coding standards defining the bes

Question

Given that all else is equal, and there are no coding standards defining the best approach, what would be the recommended way in C++ to check that a value exists and return it if it does?

For example, something like one of these declarations:

bool getMethod(double& ret);

double getMethod(bool& ok);

void getMethod(bool& ok, double& ret);

pair<bool, double> getMethod();

bool checkMethod(); // eg if (checkMethod())
double getMethod(); //        result = getMethod();
or something else, like return a struct

The value may exist about 50% of the time.

The existing code already does a lot of the last method, i.e. using a checkMethod() but I was wondering if that's really an efficient way to do it - via two calls (half the time).

Explanation / Answer

Given that all else is equal, and there are no coding standards defining the best approach, what would be the recommended way in C++ to check that a value exists and return it if it does?

Starting from C++14, you can use std::optional. (until then, you can use boost::optional).

The class behaves like a pointer, but allocates no dynamic memory and expresses explicitly the fact that the value can be missing:

The following code snippets perform the same function:

bool getMethod(double& ret); // from your code
// client code:
double result = 0.;
if(getMethod(result)) {
// result has a valid value
}
and:

#include <optional>
std::optional<double> getMethod();
if(auto result = getMethod()) {
// *result is a valid value
}

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