CODEWITHSUNDEEP
c++c++11
E. Vakili
E. Vakili

Reputation: 1096

Using string literals without using namespace std

There's recommendation in C++ community to not to use using namespace std;. But suppose you want to use string literals e.g. auto s = "dummy"s;. Not using using namespace std; cause to failed compile. What is the solution?

Upvotes: 54

Views: 20257

Answers (4)

ebasconp
ebasconp

Reputation: 1648

I would add the "using namespace" thing inside my block of code:

auto get_greetings()
{
    using namespace std::string_literals;
    return "Hello world"s;
}

So, the probability of having operator""s overloaded in some library should be ZERO, because the standard suggests we ordinary people should add a suffix with an underscore. And, since I am adding this using namespace inside my function, no probability of name clashes will occur outside it.

Upvotes: 2

Rakete1111
Rakete1111

Reputation: 48958

operator""s is in 2 inlined namespaces in namespace std. It basically looks like this:

namespace std
{
    inline namespace literals
    {
        inline namespace string_literals
        {
            //operator""s implementation
            //...
        }
    }
}

So, to only get the string literals, use using namespace std::string_literals;.

Alternatevely, if you want to include every literal - including the string literals (like s for seconds if you include chrono, ...): using namespace std::literals;.

Depending on the situation, you might also consider using:

using std::string_literals::operator""s;

instead of importing every name from that namespace.

Note that you should still not include it in a header, at global level (but you can do it inside inline or member functions or namespaces you control)

Upvotes: 55

Galik
Galik

Reputation: 48625

For string literals you can use:

using namespace std::string_literals;

That will pull about 4 names into the namespace which is fine. But when you do:

using namespace std;

Then you pull in thousands of names, many of which are commonly used in programs like count and time. This can create hard to find bugs from accidentally referring to the wrong thing.

That's not an issue with the string literals.

Also none of the names that using namespace std::string_literals; brings in should interfere with user defined names because user defined string literals must begin with _ (according to the standard) which avoids conflicts.

However you should still avoid using namespace std::string_literals; in the global namespace of a header file because you should not impose any feature on a user that they don't request.

Upvotes: 14

Shravan40
Shravan40

Reputation: 9898

Above operators are declared in the namespace std::literals::string_literals, where both literals and string_literals are inline namespaces. Access to these operators can be gained with using namespace std::literals, using namespace std::string_literals, and using namespace std::literals::string_literals

Source : std::literals::string_literals::operator""s

Upvotes: 3

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