Re: [boost] Optional library

However when I run boost::optional<int> i= 5; cout << get_optional_value_or(i, 7) ; I get the output as 5. And when I run boost::optional<int> i= {}; cout << get_optional_value_or(i, 7) ; I get the output as 7. On Sun, 19 Jan, 2020, 5:29 PM anshu khare, wrote:

When I run the following code :

int i = {}; boost::optional<int> v = i; cout << get_optional_value_or(v, 1)

I get a compilation error in the third line.

On Sun, 19 Jan, 2020, 5:12 PM Mateusz Loskot via Boost, < boost@lists.boost.org> wrote:

...

On Sun, 19 Jan 2020 at 11:57, anshu khare via Boost wrote:

...

But when I run

const std::string i = {}; boost::optional str = i; cout << get_optional_value_or(str, "some other string") ;

The output is an empty string. Shouldn't it give "some other string as output"

No, it should not.

From the documentation: "Class template optional is a wrapper for representing 'optional' (or 'nullable') objects who may not (yet) contain a valid value."

An empty string in `i` variable IS a valid value, so `str` is set with a valid value, Since it is valid value, get_optional_value_or returns that valid value and not the "some other string".

...

because if I run the same code with integer it gives the second parameter of get_optional_value_or() as output?

Are you sure?

This is expected to print 0, the valid value of `i` and not the default 1:

int i = {}; boost::optional<int> v = i; cout << get_optional_value_or(v, 1);

Best regards, -- Mateusz Loskot, http://mateusz.loskot.net

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