libstdc++-v3/docs/html/17_intro/C++STYLE

   1
   2 C++ Standard Library Style Guidelines  DRAFT 2001-01-15
   3 -------------------------------------
   4
   5 This library is written to appropriate C++ coding standards.  As such,
   6 it is intended to precede the recommendations of the GNU Coding
   7 Standard, which can be referenced here:
   8
   9 http://www.gnu.org/prep/standards_toc.html
  10
  11 ChangeLog entries for member functions should use the
  12 classname::member function name syntax as follows:
  13
  14 1999-04-15  Dennis Ritchie  <dr@att.com>
  15
  16         * src/basic_file.cc (__basic_file::open): Fix thinko in
  17         _G_HAVE_IO_FILE_OPEN bits.
  18
  19 Notable areas of divergence from what may be previous local practice
  20 (particularly for GNU C) include:
  21
  22 01. Pointers and references
  23   char* p = "flop";
  24   char& c = *p;
  25      -NOT-
  26   char *p = "flop";  // wrong
  27   char &c = *p;      // wrong
  28
  29     Reason: In C++, definitions are mixed with executable code.  Here,
  30             p is being initialized, not *p.  This is near-universal
  31             practice among C++ programmers; it is normal for C hackers
  32             to switch spontaneously as they gain experience.
  33
  34 02. Operator names and parentheses
  35   operator==(type)
  36      -NOT-
  37   operator == (type)  // wrong
  38
  39     Reason: The == is part of the function name.  Separating
  40             it makes the declaration look like an expression.
  41
  42 03. Function names and parentheses
  43   void mangle()
  44      -NOT-
  45   void mangle ()  // wrong
  46
  47      Reason: no space before parentheses (except after a control-flow
  48      keyword) is near-universal practice for C++.  It identifies the
  49      parentheses as the function-call operator or declarator, as
  50      opposed to an expression or other overloaded use of parentheses.
  51
  52 04. Template function indentation
  53   template<typename T>
  54     void
  55     template_function(args)
  56     { }
  57       -NOT-
  58   template<class T>
  59   void template_function(args) {};
  60
  61      Reason: In class definitions, without indentation whitespace is
  62              needed both above and below the declaration to distinguish
  63              it visually from other members.  (Also, re: "typename"
  64              rather than "class".)  T often could be int, which is
  65              not a class.  ("class", here, is an anachronism.)
  66
  67 05. Template class indentation
  68   template<typename _CharT, typename _Traits>
  69     class basic_ios : public ios_base
  70     {
  71     public:
  72       // Types:
  73     };
  74   -NOT-
  75   template<class _CharT, class _Traits>
  76   class basic_ios : public ios_base
  77     {
  78     public:
  79       // Types:
  80     };
  81   -NOT-
  82   template<class _CharT, class _Traits>
  83     class basic_ios : public ios_base
  84   {
  85     public:
  86       // Types:
  87   };
  88
  89 06. Enumerators
  90   enum
  91   {
  92     space = _ISspace,
  93     print = _ISprint,
  94     cntrl = _IScntrl
  95   };
  96   -NOT-
  97   enum { space = _ISspace, print = _ISprint, cntrl = _IScntrl };
  98
  99 07. Member initialization lists
 100    All one line, separate from class name.
 101
 102   gribble::gribble()
 103   : _M_private_data(0), _M_more_stuff(0), _M_helper(0);
 104   { }
 105   -NOT-
 106   gribble::gribble() : _M_private_data(0), _M_more_stuff(0), _M_helper(0);
 107   { }
 108
 109 08. Try/Catch blocks
 110   try
 111     {
 112       //
 113     }
 114   catch (...)
 115     {
 116       //
 117     }
 118   -NOT-
 119   try {
 120     //
 121   } catch(...) {
 122     //
 123   }
 124
 125 09. Member functions declarations and defintions
 126    Keywords such as extern, static, export, explicit, inline, etc
 127    go on the line above the function name. Thus
 128
 129   virtual int
 130   foo()
 131   -NOT-
 132   virtual int foo()
 133
 134         Reason: GNU coding conventions dictate return types for functions
 135         are on a separate line than the function name and parameter list
 136         for definitions. For C++, where we have member functions that can
 137         be either inline definitions or declarations, keeping to this
 138         standard allows all member function names for a given class to be
 139         aligned to the same margin, increasing readibility.
 140
 141
 142 10. Invocation of member functions with "this->"
 143    For non-uglified names, use this->name to call the function.
 144
 145   this->sync()
 146   -NOT-
 147   sync()
 148
 149         Reason: Koenig lookup.
 150
 151 11. Namespaces
 152   namespace std
 153   {
 154     blah blah blah;
 155   } // namespace std
 156
 157   -NOT-
 158
 159   namespace std {
 160     blah blah blah;
 161   } // namespace std
 162
 163 12. Spacing under protected and private in class declarations:
 164    space above, none below
 165    ie
 166
 167    public:
 168      int foo;
 169
 170    -NOT-
 171    public:
 172
 173      int foo;
 174
 175 13. Spacing WRT return statements.
 176    no extra spacing before returns
 177    ie
 178
 179    }
 180    return __ret;
 181
 182    -NOT-
 183    }
 184
 185    return __ret;
 186
 187 14. Location of global variables.
 188    All global variables of class type, whether in the "user visable"
 189    space (e.g., cin) or the implementation namespace, must be defined
 190    as a character array with the appropriate alignment and then later
 191    re-initialized to the correct value.
 192
 193    This is due to startup issues on certain platforms, such as AIX.
 194    For more explanation and examples, see src/globals.cc.  All such
 195    variables should be contained in that file, for simplicity.
 196
 197
 198
 199 The library currently has a mixture of GNU-C and modern C++ coding
 200 styles.  The GNU C usages will be combed out gradually.
 201
 202 Name patterns:
 203
 204 For nonstandard names appearing in Standard headers, we are constrained
 205 to use names that begin with underscores.  This is called "uglification".
 206 The convention is:
 207
 208   Local and argument names:  __[a-z].*
 209
 210     Examples:  __count  __ix  __s1
 211
 212   Type names and template formal-argument names: _[A-Z][^_].*
 213
 214     Examples:  _Helper  _CharT  _N
 215
 216   Member data and function names: _M_.*
 217
 218     Examples:  _M_num_elements  _M_initialize ()
 219
 220   Static data members, constants, and enumerations: _S_.*
 221
 222     Examples: _S_max_elements  _S_default_value
 223
 224 Don't use names in the same scope that differ only in the prefix,
 225 e.g. _S_top and _M_top.  See BADNAMES for a list of forbidden names.
 226 (The most tempting of these seem to be and "_T" and "__sz".)
 227
 228 Names must never have "__" internally; it would confuse name
 229 unmanglers on some targets.  Also, never use "__[0-9]", same reason.
 230
 231 --------------------------
 232
 233 [BY EXAMPLE]
 234
 235 #ifndef  _HEADER_
 236 #define  _HEADER_ 1
 237
 238 namespace std
 239 {
 240   class gribble
 241   {
 242   public:
 243     // ctor, op=, dtor
 244     gribble() throw();
 245
 246     gribble(const gribble&);
 247
 248     explicit
 249     gribble(int __howmany);
 250
 251     gribble&
 252     operator=(const gribble&);
 253
 254     virtual
 255     ~gribble() throw ();
 256
 257     // argument
 258     inline void
 259     public_member(const char* __arg) const;
 260
 261     // in-class function definitions should be restricted to one-liners.
 262     int
 263     one_line() { return 0 }
 264
 265     int
 266     two_lines(const char* arg)
 267       { return strchr(arg, 'a'); }
 268
 269     inline int
 270     three_lines();  // inline, but defined below.
 271
 272     // note indentation
 273     template<typename _Formal_argument>
 274       void
 275       public_template() const throw();
 276
 277     template<typename _Iterator>
 278       void
 279       other_template();
 280
 281   private:
 282     class _Helper;
 283
 284     int _M_private_data;
 285     int _M_more_stuff;
 286     _Helper* _M_helper;
 287     int _M_private_function();
 288
 289     enum _Enum
 290       {
 291         _S_one,
 292         _S_two
 293       };
 294
 295     static void
 296     _S_initialize_library();
 297   };
 298
 299 // More-or-less-standard language features described by lack, not presence:
 300 # ifndef _G_NO_LONGLONG
 301   extern long long _G_global_with_a_good_long_name;  // avoid globals!
 302 # endif
 303
 304   // Avoid in-class inline definitions, define separately;
 305   // likewise for member class definitions:
 306   inline int
 307   gribble::public_member() const
 308   { int __local = 0; return __local; }
 309
 310   class gribble::_Helper
 311   {
 312     int _M_stuff;
 313
 314     friend class gribble;
 315   };
 316 }
 317
 318 // Names beginning with "__": only for arguments and
 319 //   local variables; never use "__" in a type name, or
 320 //   within any name; never use "__[0-9]".
 321
 322 #endif /* _HEADER_ */
 323
 324
 325 namespace std
 326 {
 327   template<typename T>  // notice: "typename", not "class", no space
 328     long_return_value_type<with_many, args>
 329     function_name(char* pointer,               // "char *pointer" is wrong.
 330                   char* argument,
 331                   const Reference& ref)
 332     {
 333       // int a_local;  /* wrong; see below. */
 334       if (test)
 335       {
 336           nested code
 337       }
 338
 339       int a_local = 0;  // declare variable at first use.
 340
 341       //  char a, b, *p;   /* wrong */
 342       char a = 'a';
 343       char b = a + 1;
 344       char* c = "abc";  // each variable goes on its own line, always.
 345
 346       // except maybe here...
 347       for (unsigned i = 0, mask = 1; mask; ++i, mask <<= 1) {
 348           // ...
 349       }
 350     }
 351
 352   gribble::gribble()
 353   : _M_private_data(0), _M_more_stuff(0), _M_helper(0);
 354   { }
 355
 356   inline int
 357   gribble::three_lines()
 358   {
 359     // doesn't fit in one line.
 360   }
 361 } // namespace std
 362
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 364
 365
 366