"namespace std {}" before "using namespace std;"

Question

I have seen the syntax below in many places where STL classes are used without explicitly qualifying them with std::. What is the advantage of the initial namespace std {}? Why not just put using namespace std;?

namespace std {}
using namespace std;

@Steephen: What? How? The OP's question is not addressed at all in that "duplicate", as far as I can tell. — Benjamin Lindley
– Benjamin Lindley, Commented Jul 5, 2015 at 0:37
@BenjaminLindley You are right, I didn't read question clearly. Reverted my closing vote. — Steephen
– Steephen, Commented Jul 5, 2015 at 0:41

flogram_dev · Accepted Answer · 2015-07-05 00:39:14Z

10

namespace std {} simply declares the namespace so that the compiler knows about it and doing using namespace std; won't cause an error.

Later in the code stuff from std:: can be #included and they can be automatically referred to without the std:: prefix.

answered Jul 5, 2015 at 0:39

flogram_dev

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1 Comment

Arne Mertz Over a year ago

That would mean the includes come after the using directive, which is a very bad thing to do - it can change the meaning of code in those headers!

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