The All-in-One Guide to C++20/

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Named Initialization of Class Members

Named Initialization of Class Members

Get the details of designated initialization in C++20.

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Designated initialization enables the direct initialization of members of a class type using their names. For a union, only one initializer can be provided. As for aggregate initialization, the sequence of initializers in the curly braces has to match the declaration order of the members.

Designated initialization

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#include <iostream>
struct Point2D { 
    int x;
    int y; 
};
class Point3D { 
    public:
        int x; 
        int y; 
        int z;
}; 
int main() {
    std::cout << '\n';
    
    Point2D point2D{.x = 1, .y = 2};
    Point3D point3D{.x = 1, .y = 2, .z = 3};
    std::cout << "point2D: " << point2D.x << " " << point2D.y << '\n';
    std::cout << "point3D: " << point3D.x << " " << point3D.y << " "
                             << point3D.z << '\n';
    std::cout << '\n';
}

Line 18 and 19 use designated initializers to initialize the aggregates. The initializers such as .x or .y are often called designators.

The members of the aggregate can already have ...