Lære Nested Namespaces and Using Directives

Nested namespaces allow you to organize related code hierarchically, making it easier to manage large projects and prevent name collisions. In the example above, the graphics namespace contains two nested namespaces: shapes and colors. Each nested namespace groups related functions together, such as drawCircle and drawSquare within shapes, and setRed within colors.

main.cpp


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#include <iostream>

namespace graphics {
    namespace shapes {
        void drawCircle() { std::cout << "Drawing a circle." << std::endl; }
        void drawSquare() { std::cout << "Drawing a square." << std::endl; }
    }

    namespace colors {
        void setRed() { std::cout << "Color set to red." << std::endl; }}
}

int main()
{
    // Accessing nested namespaces with full qualification
    graphics::shapes::drawCircle();
    graphics::colors::setRed();

    // Using directive to simplify access to nested namespace
    using namespace graphics::shapes;
    drawSquare(); // Now accessible without full qualification
}

Using directives, such as using namespace graphics::shapes;, can simplify your code by allowing you to access functions like drawSquare without writing the full namespace path every time. This can make your code shorter and easier to read, especially when you need to use many functions from the same namespace.

However, using directives also come with risks:

When you use using namespace at a global scope, you expose all the names from that namespace to the current scope;
This can lead to name collisions and make it harder to determine where a specific function or variable comes from;
This is especially problematic in large projects or when combining code from multiple libraries.

For this reason, it is generally best to use using namespace only in limited scopes, such as within a function, and to avoid placing it at the top of header files or in global code.

By understanding how to use nested namespaces and using directives appropriately, you can keep your code organized and maintainable while avoiding common pitfalls.

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