For debugging purposes, I was writing a function which iterates over a vector of optional variables of any type to check which ones were initialized, but the check for has_value() on all of them is returning true, despite no value having ever been assigned to some of them. I’d appreciate any help pointing out what I’m misunderstanding, as I’m new to C++. The code is below. Note that when the commented line is uncommented, the if statement picks up that the variable had no value.
#include <iostream>
#include <optional>
#include <any>
bool SimpleCheck(std::vector<std::optional<std::any>> toCheck)
{
bool res = false;
for (int i = 0; i < toCheck.size(); ++i)
{
// toCheck[i] = std::nullopt;
if (!toCheck[i].has_value())
{
std::cout << "item at index " << i << " had no value\n";
res = true;
}
}
return res;
}
int main()
{
std::optional<int> i = 5;
std::optional<std::string> str;
std::optional<double> doub = std::nullopt;
bool check = SimpleCheck({i, str, doub});
std::cout << check << "\n";
return 0;
}
My expected output is:
item at index 1 had no value
item at index 2 had no value
1
The actual output is:
0
If the commented line is uncommented, the output is:
item at index 0 had no value
item at index 1 had no value
item at index 2 had no value
1
>Solution :
With
std::optional<double> doub = std::nullopt;
std::optional<std::any> a = doub; // it is not a copy constructor
a is non empty, but its any is an empty std::optional.