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In my classes in C++ so far we have been using
I see other examples of code where certain keywords are prefaced with std: instead of using the above declaration. Why is this; and what is the difference between the two? Are they interchangeable?Code:using namespace std;
Thanks!
Thestatement tells the compiler "if you can find a name in the namespace std, use it".Code:using namespace std;
Usingdoesn't let the compiler use anything else out of the "std" namespace. Simply put, it's more restrictive.Code:std::cout << x;
You can also use:
to tell the compiler that "if you need a cout, you may use the one out of the std namespace".Code:using std::cout;
Namespaces in general are intended to avoid "name-collisions" - if you have two items (functions, classes, structs, varables or whatever it may be) with the same name, the compiler [or linker] can potentially pick up either. Namespaces allow us to separte two different "names" that are otherwise the same.
It also can allow us to have alternative versions of something with only the namespace deciding which you get.
In most cases, it's probably completely equal which one we choose to use.
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Mats
if u dont put "using namespace std;" on top, then you will have to put "std::" in everything below, or the compiler cant recognize the cout<< and other things.
True - if you use anything that is part of the standard library, then you must tell the compiler that you want it to look for things in std namespace one way or another. For relatively small programs, it's usually "best" to use "using namespace std", whilst in a large program it may be better to avoid that.Quote:
Originally Posted by eastmus
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Mats
There's been interesting discussions about this here before. Search for using namespace std and read through some of the longer threads to get a selection of opinions.