c++ - What exactly is a namespace and why is it necessary

Question

I am learning C++ right now, and at the beginning of every project my instructor puts a line that says:

using namespace std;

I understand that it keeps you from having to call functions in headers you include with their header name like iostream::stdout and instead just call stdout.

But what exactly does the line tell C++ to do. What is a namespace and what is std?

I am also new to programming besides python so switching to a new paradigm is very confusing for me.

Answer 1

From cppreference.com:

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.

A namespace works to avoid names conflicts, for example the standard library defines sort() but that is a really good name for a sorting function, thanks to namespaces you can define your own sort() because it won't be in the same namespace as the standard one.

The using directive tells the compiler to use that namespace in the current scope so you can do

int f(){
    std::cout << "out!" << std::endl;
}

or:

int f(){
    using namespace std;
    cout << "out!" << endl;
}

it's handy when you're using a lot of things from another namespace.

source: Namespaces - cppreference.com