Namespaces.md

Namespaces in C++

Namespaces are designed to solve naming conflicts!! That is it!

cppreference for Namespaces

Namespaces provide a method for preventing name conflicts in large projects.

Symbols declared inside a namespace block are placed in a named scope that prevents them from being mistaken for identically-named symbols in other scopes.

Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope.

The C Language doesn't have namespace (or something similar), that is why libraries that support C normally have the name of the library embbeded into their symbols (functions, variables) .e.g. gl_init from OpenGL.

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

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

int main()
{
    apple::print("Printing in apple!");
    orange::print("Print Backwards in Orange");
    std::cin.get();
}

To avoid multiple nesting levels of indentations, could be interesting to write all our namespaces in one single line.!

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

int main()
{
    first::second::third::print("Inception");
    std::cin.get();
}

Or for c++17

namespace Q {
  namespace V { // V is a member of Q, and is fully defined within Q
// namespace Q::V { // C++17 alternative to the above two lines

Using keyword and namespace alias

We can use the keywork using to specify what will be the default namespace used in some scope, or to create some alias for that namespace.

As a suggestion it's good to keep the scope of using as minimal as possible. As a good rule of thumb, never use using in header files, because this will against the purpose of the namespaces, which is to avoid name conflicts.

// a is now an alias for apple, and used outside of main scope.
namespace a = apple;

int main()
{
    // just for the scope of main()
    using namespace std;
    cout << "Hello" << endl;
    a.print();
}