61 Namespaces in C++

1. Why Use Namespace

void print(const char* text)
{
    std::cout << text << std::endl;
}

void print(const char* text)
{
    std::string temp = text;
    std::reverse(temp.begin(),temp.end());
    std::cout << temp << std::endl;
}

Here we have two functions with the same function signature. The symbols for these two functions are identical, which would result in linking or compilation errors if placed in the same file. However, if we indeed want two print functions, or if we are using a library that already defines a print function but we want our own version, we need a way to differentiate them.

C language does not have namespaces. For example, when using the GLFW library (a C-based OpenGL library), every function name is prefixed with GLFW.

Thus, the primary purpose of a namespace is to avoid naming conflicts.

Namespaces can be nested in a single line, which can improve readability when dealing with multiple layers of nesting:

namespace apple { namespace functions {

    void print(const char* text)
    {
        std::cout << text << std::endl;
    }
} }

The :: operator is the namespace resolution operator. Classes are also a form of namespace, which is why you use :: to access members like nested classes within another class.

You can also selectively introduce functions:

You can also alias namespaces:

It is advisable to limit the scope of a namespace to a small area and avoid placing it in header files.