cout and std::cout

This is a discussion on cout and std::cout within the C++ Programming forums, part of the General Programming Boards category; What is the difference between cout and std::cout? Thanks.....

  1. #1
    Registered User
    Join Date
    Dec 2006
    Location
    Jacksonville, AR
    Posts
    91

    Smile cout and std::cout

    What is the difference between cout and std::cout?
    Thanks..

  2. #2
    and the hat of wrongness Salem's Avatar
    Join Date
    Aug 2001
    Location
    The edge of the known universe
    Posts
    32,417
    One uses the cout defined in whatever namespace you said you were using, eg.
    using namespace std; would get you to std::cout

    using namespace foo; would get you to foo::cout


    If you use std::cout, you always get what you asked for.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  3. #3
    Registered User
    Join Date
    Dec 2006
    Location
    Jacksonville, AR
    Posts
    91

    Smile

    Okay.. so if I want to use just cout, what namespace should I use?
    Thanks for replying, Salem..

  4. #4
    pwns nooblars
    Join Date
    Oct 2005
    Location
    Portland, Or
    Posts
    1,094
    You should use it as std::cout unless you have a good reason for exposing the whole namespace.

  5. #5
    Code Goddess Prelude's Avatar
    Join Date
    Sep 2001
    Posts
    9,796
    >so if I want to use just cout, what namespace should I use?
    It should look like this:
    Code:
    #include <iostream>
    
    int main()
    {
      std::cout<<"I'm using cout\n";
    }
    My best code is written with the delete key.

  6. #6
    Registered User
    Join Date
    Jan 2005
    Posts
    7,317
    I prefer to use std::cout (and std::cin and std::string, etc). But many beginner programs use the using directive, which looks like this:
    Code:
    #include <iostream>
    using namespace std;
    
    int main()
    {
      cout<<"I'm using cout\n";
    }
    My advice is to always add the std:: to your standard library names, but it's not that bad if you prefer this solution for small programs.

  7. #7
    and the hat of wrongness Salem's Avatar
    Join Date
    Aug 2001
    Location
    The edge of the known universe
    Posts
    32,417
    using namespace std;
    is a convenient compatibility hack for old-standard C++ which didn't have any namespaces at all, and thus means you don't have to re-write the code to put std:: in front of everything.

    But as your programs become more complex, and you start using multiple namespaces, blanket "using namespace" is a disaster waiting to happen.

    You can (at a pinch) also write
    using std::cout;
    then write
    cout << "Hello world" << std::endl;
    if you want the convenience of the short-form for your most used members of the standard namespace.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  8. #8
    Kernel hacker
    Join Date
    Jul 2007
    Location
    Farncombe, Surrey, England
    Posts
    15,677
    Quote Originally Posted by Salem View Post
    using namespace std;
    is a convenient compatibility hack for old-standard C++ which didn't have any namespaces at all, and thus means you don't have to re-write the code to put std:: in front of everything.

    But as your programs become more complex, and you start using multiple namespaces, blanket "using namespace" is a disaster waiting to happen.

    You can (at a pinch) also write
    using std::cout;
    then write
    cout << "Hello world" << std::endl;
    if you want the convenience of the short-form for your most used members of the standard namespace.
    I kind of like this bit when writing stuff that does lots of output, so you can easily use cout << ... << endl; but it's still (fairly) clear which cout you intend to be used.

    This resembles the model [if I remember right] that is used in for example Modula-2 where you specify which modules you want to take which function(s) from.

    And of course, should you find that you want to use foo::cout instead of std::cout [say], you only need to make one change in the file.

    [And you can of course still mix foo::cout and std::cout in the same source file].

    But maybe that's just because I'm a bit lazy.

    --
    Mats
    Compilers can produce warnings - make the compiler programmers happy: Use them!
    Please don't PM me for help - and no, I don't do help over instant messengers.

  9. #9
    Registered User
    Join Date
    Sep 2007
    Posts
    37
    Quote Originally Posted by Salem View Post
    But as your programs become more complex, and you start using multiple namespaces, blanket "using namespace" is a disaster waiting to happen.
    Whats a namespace anyways? Our school is retarded, we are taught C++ on Borland Turbo C++ 4.5 (some other noobs learn on the DOS version 2.x)...Only lately I started using the BloodShed DevC++ and Code::Blocks...and learnt the using namespace std; line, thinking it as a part of the new syntax >.> Same for void main/int main..whatever happened?
    Last edited by ultrabot90; 09-22-2007 at 01:26 AM.

  10. #10
    Sweet
    Join Date
    Aug 2002
    Location
    Tucson, Arizona
    Posts
    1,801
    A namespace separates functions into there own scope so to speak.

    Code:
    namespace abc
    {
         int getValue()
        {
            return 10;
        }
    }
    namespace qwe
    {
        string getValue()
        {
            return "Hello";
        }
    }
    you can safely call the proper getValue depending on the namespace you choose to use

  11. #11
    and the hat of wrongness Salem's Avatar
    Join Date
    Aug 2001
    Location
    The edge of the known universe
    Posts
    32,417
    > Whats a namespace anyways?
    Suppose you want to use a graphics library and a sound library.
    Suppose that for some reason, they both implemented a function called Read().

    In C and old C++, what results is a complete mess of multiply declared symbols, the wrong code being called, and general "wtf" all round. The problem could usually be solved, but it was always an improvised hack.

    Originally, people who knew such things were bound to happen prefixed all their public symbols, so we ended up with SndRead() and GraRead(). But that was somewhat cumbersome to implement and things occasionally slipped through.

    Namespaces provide an automatic way of generating these prefixes for the whole interface in one go, and gives you the flexibility of using the long or short form names.

    So where you previously used SndRead(), you would instead use Snd::Read(), or having established a prior "using" clause, just Read()
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  12. #12
    Registered User
    Join Date
    Sep 2007
    Posts
    37
    Quote Originally Posted by Salem View Post
    In C and old C++, what results is a complete mess of multiply declared symbols, the wrong code being called, and general "wtf" all round. The problem could usually be solved, but it was always an improvised hack.
    lmfao THAT would explain a lot...and any idea on the trend of the necessary int main? I mean, 'main must return a value', all that.

  13. #13
    Registered User
    Join Date
    Jun 2005
    Posts
    6,157
    main() was specified to return int from day one (i.e. when C was first created, well before it was ever standardised). The C and C++ standards still require that compilers support main() returning int.

    void main() is, and always has been, a non-standard extension support by some compilers. Historically, the vendors of a couple of those compilers attempted to influence the content of the standards, so their help files stated falsely that void main() is/was standard, and most of the code examples supplied by those vendors still use void main(). The standards have never adopted void main().

  14. #14
    and the hat of wrongness Salem's Avatar
    Join Date
    Aug 2001
    Location
    The edge of the known universe
    Posts
    32,417
    void main only ever came about because of crappy DOS, incapable of running more than one program at once, and having a shell which was utterly incapable of dealing with the exit status of programs.
    If you dance barefoot on the broken glass of undefined behaviour, you've got to expect the occasional cut.
    If at first you don't succeed, try writing your phone number on the exam paper.
    I support http://www.ukip.org/ as the first necessary step to a free Europe.

  15. #15
    and the hat of sweating
    Join Date
    Aug 2007
    Location
    Toronto, ON
    Posts
    3,545
    Quote Originally Posted by Salem View Post
    void main only ever came about because of crappy DOS, incapable of running more than one program at once, and having a shell which was utterly incapable of dealing with the exit status of programs.
    If DOS can't deal with program return codes, then how does the ERRORLEVEL variable in batch files get its value?

Page 1 of 2 12 LastLast
Popular pages Recent additions subscribe to a feed

Similar Threads

  1. Binding cout?
    By Elysia in forum C++ Programming
    Replies: 14
    Last Post: 10-16-2008, 06:41 AM
  2. New, making a survey program
    By shaffer in forum C++ Programming
    Replies: 18
    Last Post: 12-01-2006, 10:36 AM
  3. Binary I/O with cin and cout
    By The Urchin in forum C++ Programming
    Replies: 4
    Last Post: 10-24-2006, 12:47 PM
  4. cout vs std::cout
    By none in forum C++ Programming
    Replies: 10
    Last Post: 07-26-2004, 11:20 PM
  5. Whats the difference between cout and std::cout?
    By mdshort in forum C++ Programming
    Replies: 10
    Last Post: 12-30-2003, 04:34 PM

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21