Designated Initializers

Initialize struct members by name

Example Code

cpp

#include <iostream>
#include <string>
struct Config {
    std::string host = "localhost";
    int port = 8080;
    bool ssl = false;
    int timeout = 30;
    int max_connections = 100;
};
struct Point3D {
    double x = 0;
    double y = 0;
    double z = 0;
};
int main() {
    // Designated initializers - clear and self-documenting
    Config server_config{
        .host = "api.example.com",
        .port = 443,
        .ssl = true,
        // timeout uses default value
        .max_connections = 1000
    };
    
    std::cout << "Host: " << server_config.host << std::endl;
    std::cout << "Port: " << server_config.port << std::endl;
    std::cout << "Timeout: " << server_config.timeout << std::endl;  // 30
    
    // Partial initialization
    Point3D point{.y = 5.0};  // x=0, y=5, z=0
    
    std::cout << "Point: (" << point.x << ", " 
              << point.y << ", " << point.z << ")" << std::endl;
    
    return 0;
}

Explanation

Designated initializers allow initializing struct members by name, making code clearer and less error-prone. Members must be initialized in declaration order, and unspecified members use their default values.

Key Points

1Use .member_name = value syntax
2Members must be in declaration order
3Skipped members use default values
4Makes code self-documenting