Recently i've noticed that if I don't include the 'using namespace std' in my program and just use 'std::cout' or 'std::endl' then my program still compiles just fine? Therefore if I use the 'std::' prefix is it even necessary to include the 'using namespace std'? Does the 'std::' prefix call the using namespace std? If someone can clear this up for me it would be greatly appreciated.
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2I suspect it's a duplicate of this Q&A https://stackoverflow.com/questions/1265039/using-std-namespace – StoryTeller - Unslander Monica Apr 21 '19 at 06:27
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1`std::stuff` just uses `stuff` from namespace `std`. – sjsam Apr 21 '19 at 06:28
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2You may also benefit from getting a good [c++ book](https://stackoverflow.com/questions/388242/the-definitive-c-book-guide-and-list). That should definitely clear any all confusion you have. – StoryTeller - Unslander Monica Apr 21 '19 at 06:29
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5Possible duplicate of [Why is "using namespace std" considered bad practice?](https://stackoverflow.com/questions/1452721/why-is-using-namespace-std-considered-bad-practice) – sjsam Apr 21 '19 at 06:29
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2If you never use `using namespace std;` you'll be much happier. – Retired Ninja Apr 21 '19 at 06:30
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2Possible duplicate of [Using std Namespace](https://stackoverflow.com/questions/1265039/using-std-namespace) – Igor R. Apr 21 '19 at 06:31
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None of these proposed duplicates actually say what `std::` means, which seems to be the confusion. – Daniel H Apr 21 '19 at 06:35
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In C++, :: is called the "scope resolution operator", so std::cout means "The variable cout, which can be found inside std".
The using namespace std; directive means "For any name you can't find, also try looking it up in std". Thus, if you explicitly say std::cout (and equivalent for everything else in the std namespace), then you don't need using namespace std.
As others have said, it's usually considered bad style to use using namespace std;, because a lot of the names in std are things you might want to use elsewhere, for example std::count. A compromise option is to instead say using std::cout;, which will tell the compiler to look for cout in std but not anything else.
There's debate about whether to say using std::cout or just write std::cout everywhere you need it in your main C++ file, but most people believe that you should rarely if ever use using namespace. If you're writing a header file, though, you should never use a using directive at the top level because then every file which includes yours will get it, and they might want to use different names.
Daniel H
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When you use:
using namespace std;
You're telling the program that anything that it can't find should be in the namespace std. For larger programs, this is a problem because you might be using multiple namespaces with functions that have the same name, so it's best to use std::cout for larger programs.
Kookies
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