[pf3gnuchains/gcc-fork.git] / libstdc++-v3 / docs / html / 17_intro / C++STYLE

C++ Standard Library Style Guidelines  DRAFT 2001-01-15
-------------------------------------

This library is written to appropriate C++ coding standards.  As such,
it is intended to precede the recommendations of the GNU Coding
Standard, which can be referenced here:

http://www.gnu.org/prep/standards_toc.html

ChangeLog entries for member functions should use the
classname::member function name syntax as follows:

1999-04-15  Dennis Ritchie  <dr@att.com>

        * src/basic_file.cc (__basic_file::open): Fix thinko in
        _G_HAVE_IO_FILE_OPEN bits.

Notable areas of divergence from what may be previous local practice
(particularly for GNU C) include:

01. Pointers and references
  char* p = "flop";
  char& c = *p;
     -NOT-
  char *p = "flop";  // wrong
  char &c = *p;      // wrong
  
    Reason: In C++, definitions are mixed with executable code.  Here,       
            p is being initialized, not *p.  This is near-universal
            practice among C++ programmers; it is normal for C hackers
            to switch spontaneously as they gain experience.

02. Operator names and parentheses
  operator==(type)
     -NOT-
  operator == (type)  // wrong
     
    Reason: The == is part of the function name.  Separating
            it makes the declaration look like an expression. 

03. Function names and parentheses
  void mangle()
     -NOT-
  void mangle ()  // wrong

     Reason: no space before parentheses (except after a control-flow
     keyword) is near-universal practice for C++.  It identifies the
     parentheses as the function-call operator or declarator, as 
     opposed to an expression or other overloaded use of parentheses.

04. Template function indentation
  template<typename T>
    void 
    template_function(args)
    { }
      -NOT-
  template<class T>
  void template_function(args) {};
  
     Reason: In class definitions, without indentation whitespace is
             needed both above and below the declaration to distinguish
             it visually from other members.  (Also, re: "typename"
             rather than "class".)  T often could be int, which is 
             not a class.  ("class", here, is an anachronism.)

05. Template class indentation
  template<typename _CharT, typename _Traits>
    class basic_ios : public ios_base
    {
    public:
      // Types:
    };
  -NOT-
  template<class _CharT, class _Traits>
  class basic_ios : public ios_base
    {
    public:
      // Types:
    };
  -NOT-
  template<class _CharT, class _Traits>
    class basic_ios : public ios_base
  {
    public:
      // Types:
  };

06. Enumerators
  enum
  {
    space = _ISspace,
    print = _ISprint,
    cntrl = _IScntrl
  };
  -NOT-
  enum { space = _ISspace, print = _ISprint, cntrl = _IScntrl };

07. Member initialization lists
   All one line, separate from class name.

  gribble::gribble() 
  : _M_private_data(0), _M_more_stuff(0), _M_helper(0);
  { }
  -NOT-
  gribble::gribble() : _M_private_data(0), _M_more_stuff(0), _M_helper(0);
  { }

08. Try/Catch blocks
  try 
    {
      //
    }   
  catch (...)
    {
      //
    }   
  -NOT-
  try {
    // 
  } catch(...) { 
    //
  }

09. Member functions declarations and defintions
   Keywords such as extern, static, export, explicit, inline, etc
   go on the line above the function name. Thus

  virtual int   
  foo()
  -NOT-
  virtual int foo()

        Reason: GNU coding conventions dictate return types for functions
        are on a separate line than the function name and parameter list
        for definitions. For C++, where we have member functions that can
        be either inline definitions or declarations, keeping to this
        standard allows all member function names for a given class to be
        aligned to the same margin, increasing readibility.


10. Invocation of member functions with "this->"
   For non-uglified names, use this->name to call the function.

  this->sync()
  -NOT-
  sync()

        Reason: Koenig lookup.

11. Namespaces
  namespace std
  {
    blah blah blah;
  } // namespace std

  -NOT-

  namespace std {
    blah blah blah;
  } // namespace std

12. Spacing under protected and private in class declarations:
   space above, none below
   ie

   public:
     int foo;

   -NOT-
   public:
   
     int foo;

13. Spacing WRT return statements.
   no extra spacing before returns
   ie

   }
   return __ret;

   -NOT-
   }

   return __ret;

14. Location of global variables.
   All global variables of class type, whether in the "user visable"
   space (e.g., cin) or the implementation namespace, must be defined
   as a character array with the appropriate alignment and then later
   re-initialized to the correct value.

   This is due to startup issues on certain platforms, such as AIX.
   For more explanation and examples, see src/globals.cc.  All such
   variables should be contained in that file, for simplicity.



The library currently has a mixture of GNU-C and modern C++ coding
styles.  The GNU C usages will be combed out gradually.

Name patterns:

For nonstandard names appearing in Standard headers, we are constrained 
to use names that begin with underscores.  This is called "uglification".
The convention is:

  Local and argument names:  __[a-z].*

    Examples:  __count  __ix  __s1  

  Type names and template formal-argument names: _[A-Z][^_].*

    Examples:  _Helper  _CharT  _N 

  Member data and function names: _M_.*

    Examples:  _M_num_elements  _M_initialize ()

  Static data members, constants, and enumerations: _S_.*

    Examples: _S_max_elements  _S_default_value

Don't use names in the same scope that differ only in the prefix, 
e.g. _S_top and _M_top.  See BADNAMES for a list of forbidden names.
(The most tempting of these seem to be and "_T" and "__sz".)

Names must never have "__" internally; it would confuse name
unmanglers on some targets.  Also, never use "__[0-9]", same reason.

--------------------------

[BY EXAMPLE]
    
#ifndef  _HEADER_
#define  _HEADER_ 1

namespace std
{
  class gribble
  {
  public:
    // ctor, op=, dtor
    gribble() throw();

    gribble(const gribble&);

    explicit 
    gribble(int __howmany);

    gribble& 
    operator=(const gribble&);

    virtual 
    ~gribble() throw ();

    // argument
    inline void  
    public_member(const char* __arg) const;

    // in-class function definitions should be restricted to one-liners.
    int 
    one_line() { return 0 }

    int 
    two_lines(const char* arg) 
      { return strchr(arg, 'a'); }

    inline int 
    three_lines();  // inline, but defined below.

    // note indentation
    template<typename _Formal_argument>
      void 
      public_template() const throw();

    template<typename _Iterator>
      void 
      other_template();

  private:
    class _Helper;

    int _M_private_data;
    int _M_more_stuff;
    _Helper* _M_helper;
    int _M_private_function();

    enum _Enum 
      { 
        _S_one, 
        _S_two 
      };

    static void 
    _S_initialize_library();
  };

// More-or-less-standard language features described by lack, not presence:
# ifndef _G_NO_LONGLONG
  extern long long _G_global_with_a_good_long_name;  // avoid globals!
# endif

  // Avoid in-class inline definitions, define separately;
  // likewise for member class definitions:
  inline int
  gribble::public_member() const
  { int __local = 0; return __local; }

  class gribble::_Helper
  {
    int _M_stuff;

    friend class gribble;
  };
}

// Names beginning with "__": only for arguments and
//   local variables; never use "__" in a type name, or
//   within any name; never use "__[0-9]".

#endif /* _HEADER_ */


namespace std 
{
  template<typename T>  // notice: "typename", not "class", no space
    long_return_value_type<with_many, args>  
    function_name(char* pointer,               // "char *pointer" is wrong.
                  char* argument, 
                  const Reference& ref)
    {
      // int a_local;  /* wrong; see below. */
      if (test) 
      { 
          nested code 
      }
    
      int a_local = 0;  // declare variable at first use.

      //  char a, b, *p;   /* wrong */
      char a = 'a';
      char b = a + 1;
      char* c = "abc";  // each variable goes on its own line, always.

      // except maybe here...
      for (unsigned i = 0, mask = 1; mask; ++i, mask <<= 1) {
          // ...
      }
    }
  
  gribble::gribble()
  : _M_private_data(0), _M_more_stuff(0), _M_helper(0);
  { }

  inline int 
  gribble::three_lines()
  {
    // doesn't fit in one line.
  }
} // namespace std