C++ Library - <optional>

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The <optional> header is introduced in C++17, is used to represent an object in a type-safe manner that may or may not contain a value. A common use case for optional is the return value of a function that may fail.

Provides safe methods to access the contained value and clearly signifies when a value may be optional, improving code readability.

Including <optional> Header

To include the <optional> header in your C++ program, you can use the following syntax.

 #include <optional> 

Functions of <optional> Header

Below is list of all functions from <optional> header.

S.NO	Functions & Description
1	begin This function provides an iterator to access the stored value of an optional object if it contains a value..
2	emplace This function allows you to directly construct or reconstruct the value stored in the optional object.
3	reset This function is used to clear the current state of the optional object.
4	swap This function is used to exchange the contents of the two optional objects.
5	value This function is used to retrieve the value stored in the optional object.

Swapping Optional Values

In the following example we are going to use, std::swap to exchange the values of two objects.

 #include <iostream> #include <optional> #include <algorithm> int main() { std::optional<int> a = 1; std::optional<int> b = 2; std::swap(a, b); std::cout << "a: " << *a << ", b: " << *b << "\n"; return 0; } 

Output

If we run the above code it will generate the following output

 a: 2, b: 1