As someone who writes C++ code often, I see (and use) the keyword
namespace
frequently and I think it is worth knowing what this keyword
is all about.
A namespace
is a region that provides a scope
to the identifiers
(the names of functions, variables, etc) inside it. namespaces
are used to organize code into logical groups
. All identifiers
in the namespace
scope are visible to one another.
The identifiers
in the namespace
can be accessed by bringing those said identifiers
into the current scope by using
or utilizing fully qualified names.
using namespace std;
// the namespace std is now in scope
string my_string;
std::string my_string
// fully qualified name
Declaring namespace
and namespace members
A namespace
declaration is generally done in a header file as following:
// my_namespace_declaration.h
namespace my_own_namepsace
{
void func_one();
int func_two();
}
The members of this namespace
can then be brought into scope
of any other file by fully qualified names or the using
directive. (If you want to know more about using
, checkout this article by me)
// other_file.cpp
#include"my_own_namepsace.h"
using namespace my_own_namepsace;
my_own_namepsace::func_one();
// fully qualified names are to be used
// even when bringing the namespace in
// scope with using directive
Code in a header file that uses identifiers
from other namespaces
should always use the fully qualified namespace
name to avoid ambiguity. This isocpp core guideline puts more light.
Nested namespaces
namespaces
can be nested. A nested namespace has unqualified access to its parent's members however the parent members do not have unqualified access to the nested namespace (unless it is declared as inline).
The std namespace
All C++ standard library types and functions are declared in the std namespace
or the various namespaces that are nested inside std
which makes it one of the most common namespaces
to be encountered.
This article is a short introduction and if you want to know more about namespaces
, I encourage you to head over here.
Thanks for giving this article a read and I'll see you in the next one ๐
PS: This is an article in my series Quick Introduction to a concept in C++. You can find all the articles in this series here.
Top comments (0)