concise syntax for c++ namespace

Question

I wonder if it is possible to write the following lengthy namespace usage in a more succinct way:

#include <iostream>
#include <iomanip>

using std::ostream;
using std::cout;
using std::endl;
using std::ios;
using std::setw;
using std::setfill;
using std::hex;

say:

using std::{ostream,cout,endl,ios,setw,setfill,hex}; // hypothetically, of course

Short answer: No. Is writting `std::` that big of a deal? It causes so many fewer problems when you just use the qualified names. — NathanOliver, Feb 12 '20 at 16:02
["Why is “using namespace std;” considered bad practice?"](https://stackoverflow.com/q/1452721/1171191) — BoBTFish, Feb 12 '20 at 16:05

Vlad from Moscow · Accepted Answer · 2020-02-12T16:27:58.053

4

You may write

using std::ostream, std::cout, std::endl, std::ios, std::setw, std::setfill, std::hex;

provided that your compiler supports the Standard C++ 17.

As for me then I advice to use qualified names instead of unqualified names introduced by using declarations. Unqualified names can confuse readers of the code and be reasons of ambiguities.

For example if a reader of the code will meet the name hex he will be confused whether it is the standard manipulator std::hex or a user-defined name.

Usually using declarations are used to introduce overloaded functions in a given scope or make visible names of members of base classes.

edited Feb 12 '20 at 16:27

answered Feb 12 '20 at 16:05

Vlad from Moscow

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I hope nobody is confused by unqualified names from `std`. – user253751 Feb 12 '20 at 16:10
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@user253751 You are wromng. For example if you meet the name hex it is unclear whether it is std::hex or a user-defined name. – Vlad from Moscow Feb 12 '20 at 16:11
This appears to be valid for C++17, but not earlier versions - https://en.cppreference.com/w/cpp/language/using_declaration – Fred Larson Feb 12 '20 at 16:11
Indeed this appears to be new in C++17. TIL. Please add that qualification to the answer – AndyG Feb 12 '20 at 16:13
Note that Microsoft still appears to not support this syntax even with `/std:c++latest` – AndyG Feb 12 '20 at 16:16
@AndyG No, Visual C++ 19 supports this syntax. – Vlad from Moscow Feb 12 '20 at 16:24
@VladfromMoscow [Not 19.00.23506](https://rextester.com/XPY39794) – AndyG Feb 12 '20 at 16:25
Good to know they've fixed it in 16.4 – AndyG Feb 12 '20 at 16:32

concise syntax for c++ namespace

1 Answers1