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This question may be a duplicate, but I can't find a good answer. Short and simple, what requires me to declare
using namespace std;
in C++ programs?
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namespace is needed because if a functionalities like cout is used, but not defined in the current scope computer needs to know where to check. so namespace needs to be included. Because we are writing the code outside the std namespace.
A namespace is a declarative region that provides a scope to the identifiers (names of functions, variables or other user-defined data types) inside it. Multiple namespace blocks with the same name are allowed. All declarations within those blocks are declared in the named scope.
Specify the standard namespace, for example: std::printf("example\n"); Use the C++ keyword using to import a name to the global namespace: using namespace std; printf("example\n");
It isn't. In fact, I would recommend against it. However, if you do not write using namespace std , then you need to fully qualify the names you use from the standard library. That means std::string instead of string , std::cout instead of cout , and so forth.
Since the C++ standard has been accepted, practically all of the standard library is inside the std namespace. So if you don't want to qualify all standard library calls with std::, you need to add the using directive.
However,
using namespace std;
is considered a bad practice because you are practically importing the whole standard namespace, thus opening up a lot of possibilities for name clashes. It is better to import only the stuff you are actually using in your code, like
using std::string;
Nothing does, it's a shorthand to avoid prefixing everything in that namespace with std::
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