Need clarification on using namespace

[jjwooyoung]

Hi,

A bit new to C++ and was wondering if someone can clarify something for me?

So I know that "using namespace xxx" tells the compiler to look in namespace xxx for a function if that function doesn't exist in my source code.

E.g This tells it to look in namespace std for cout

#include <iostream>
using namespace std;

int main() {
    cout "Hello";
}

But why don't we need a namespace for say iomanip? If the compiler doesn't find a function (e.g setprecision()), how would it know where to look for it?

[JLBorges]

See: Koenig look up: http://en.cppreference.com/w/cpp/language/adl

Koenig on Koenig lookup: http://www.drdobbs.com/cpp/a-personal-note-about-argument-dependent/232901443

Note: However, setprecision() needs to be qualified.
http://coliru.stacked-crooked.com/a/8ab0195030ec5273