Xref: utzoo comp.lang.c++:8589 comp.unix.i386:7158
Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!brunix!sdm
From: sdm@cs.brown.edu (Scott Meyers)
Newsgroups: comp.lang.c++,comp.unix.i386
Subject: Re: stream manipulators which take arguments: HELP!
Keywords: stream manipulators
Message-ID: <45657@brunix.UUCP>
Date: 24 Jul 90 16:28:11 GMT
References: <331@ndla.UUCP>
Sender: news@brunix.UUCP
Reply-To: sdm@cs.brown.edu (Scott Meyers)
Organization: Brown University Department of Computer Science
Lines: 45

In article <331@ndla.UUCP> platt@ndla.UUCP (Daniel E. Platt) writes:
>I'd like some information on how to write stream manipulators which
>takes arguments.  All of the documentation I currently have on C++ 2.0
>doesn't cover it (I can't really call it 'documentation,' but its what
>I have at the moment).  

From an application I have:

From the .h file:

    // ----------------------------------------------------------------------------
    // We need to create a manipulator taking a const int argument.  Because no
    // such manipulator exists by default, we have to instantiate one using the
    // IOMANIP macros.  These macros only understand simple typenames, so we have
    // to create a typedef for const int.  I figured out how to do this by
    // looking at the lengthdemo example that came with the CC 2.0 distribution.
    //
    // indent is an ostream manipulator that adds whitespace to s.  The amount
    // of whitespace is proportional to level.  indent is designed to format
    // hierarchical structures.  
    // ----------------------------------------------------------------------------
    typedef const int ConstInt;           // create simple typename
    IOMANIPdeclare(ConstInt);             // magic macro call #1
    OMANIP(ConstInt)
    indent(const int level);              // magic macro call #2
    ostream& indent(ostream& s,
                    const int level = 0); // this is the actual manip. function

From the .C file:

    const LEVEL_INDENT = 3;  // number of spaces to indent per level when 
                             //   printing out hierarchical information

    ostream& indent(ostream& s, const int level)
    {
      for (int i = level * LEVEL_INDENT; i > 0; i--) s << " ";
      return s;
    }

    OMANIP(ConstInt) indent(const int level)
    {
      return OMANIP(ConstInt)(indent,level);
    }

Scott