Why std cout instead of simply cout

Question

I get these error messages for all cout and endl   main cc 17 5  error     cout    was not declared in this scope main cc 17 5  note  suggested alternative   usr include c   4 6 iostream 62 18  note       std  cout      After following the suggestion  everything is fine  Now I am curious  why I had to do that  We used C   in classes before  but I never had to write a std   before any of those commands  What might be different on this system

User · Accepted Answer

It seems possible your class may have been using pre-standard C++. An easy way to tell, is to look at your old programs and check, do you see:

#include <iostream.h>

or

#include <iostream>

The former is pre-standard, and you'll be able to just say cout as opposed to std::cout without anything additional. You can get the same behavior in standard C++ by adding

using std::cout;

or

using namespace std;

Just one idea, anyway.

User · Answer

If you are working in ROOT  you do not even have to write  include lt iostream gt  and using namespace std  simply start from int filename     This will solve the issue

User · Answer

Everything in the Standard Template Iostream Library resides in namespace std  You ve probably used   using namespace std    In your classes  and that s why it worked

User · Answer

std  is a namespace used for STL  Standard Template Library   Please refer to https   en wikipedia org wiki Namespace Use in common languages  You can either write using namespace std  before using any stl functions  variables or just insert std   before them

User · Answer

You probably had using namespace std  before in your code you did in class  That explicitly tells the precompiler to look for the symbols in std  which means you don t need to std    Though it is good practice to std  cout instead of cout so you explicitly invoke std  cout every time  That way if you are using another library that redefines cout  you still have the std  cout behavior instead of some other custom behavior

User · Answer

In the C   standard  cout is defined in the std namespace  so you need to either say std  cout or put  using namespace std    in your code in order to get at it   However  this was not always the case  and in the past cout was just in the global namespace  or  later on  in both global and std   I would therefore conclude that your classes used an older C   compiler

User · Answer

You could use the namespace  http   www daniweb com software-development cpp threads 109029 what-its-the-use-of-using-namespace-std  But you might offend someone  Why is  quot using namespace std quot  considered bad practice

[c++] Why std::cout instead of simply cout?

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