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2 <!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"><html xmlns="http://www.w3.org/1999/xhtml"><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8" /><title>Coding Style</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.77.1" /><meta name="keywords" content="ISO C++, library" /><meta name="keywords" content="ISO C++, runtime, library" /><link rel="home" href="../index.html" title="The GNU C++ Library" /><link rel="up" href="appendix_contributing.html" title="Appendix A. Contributing" /><link rel="prev" href="source_organization.html" title="Directory Layout and Source Conventions" /><link rel="next" href="source_design_notes.html" title="Design Notes" /></head><body><div class="navheader"><table width="100%" summary="Navigation header"><tr><th colspan="3" align="center">Coding Style</th></tr><tr><td width="20%" align="left"><a accesskey="p" href="source_organization.html">Prev</a> </td><th width="60%" align="center">Appendix A.
5 </th><td width="20%" align="right"> <a accesskey="n" href="source_design_notes.html">Next</a></td></tr></table><hr /></div><div class="section"><div class="titlepage"><div><div><h2 class="title" style="clear: both"><a id="contrib.coding_style"></a>Coding Style</h2></div></div></div><p>
6 </p><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="coding_style.bad_identifiers"></a>Bad Identifiers</h3></div></div></div><p>
7 Identifiers that conflict and should be avoided.
8 </p><div class="literallayout"><p><br />
9 This is the list of names <span class="quote">“<span class="quote">reserved to the<br />
10 implementation</span>”</span> that have been claimed by certain<br />
11 compilers and system headers of interest, and should not be used<br />
12 in the library. It will grow, of course. We generally are<br />
13 interested in names that are not all-caps, except for those like<br />
56 [Note that this list is out of date. It applies to the old<br />
57 name-mangling; in G++ 3.0 and higher a different name-mangling is<br />
58 used. In addition, many of the bugs relating to G++ interpreting<br />
59 these names as operators have been fixed.]<br />
61 The full set of __* identifiers (combined from gcc/cp/lex.c and<br />
62 gcc/cplus-dem.c) that are either old or new, but are definitely<br />
63 recognized by the demangler, is:<br />
129 __postdecrement<br />
130 __postincrement<br />
147 __builtin_alloca<br />
148 __builtin_fsqrt<br />
152 __builtin_cast_f2i<br />
153 __builtin_cast_i2f<br />
154 __builtin_cast_d2ll<br />
155 __builtin_cast_ll2d<br />
156 __builtin_copy_dhi2i<br />
157 __builtin_copy_i2dhi<br />
158 __builtin_copy_dlo2i<br />
159 __builtin_copy_i2dlo<br />
160 __add_and_fetch<br />
161 __sub_and_fetch<br />
163 __xor_and_fetch<br />
164 __and_and_fetch<br />
165 __nand_and_fetch<br />
166 __mpy_and_fetch<br />
167 __min_and_fetch<br />
168 __max_and_fetch<br />
169 __fetch_and_add<br />
170 __fetch_and_sub<br />
172 __fetch_and_xor<br />
173 __fetch_and_and<br />
174 __fetch_and_nand<br />
175 __fetch_and_mpy<br />
176 __fetch_and_min<br />
177 __fetch_and_max<br />
178 __lock_test_and_set<br />
181 __compare_and_swap<br />
183 __high_multiply<br />
190 __embedded_cplusplus<br />
191 // long double conversion members mangled as __opr<br />
192 // http://gcc.gnu.org/ml/libstdc++/1999-q4/msg00060.html<br />
194 </p></div></div><div class="section"><div class="titlepage"><div><div><h3 class="title"><a id="coding_style.example"></a>By Example</h3></div></div></div><div class="literallayout"><p><br />
195 This library is written to appropriate C++ coding standards. As such,<br />
196 it is intended to precede the recommendations of the GNU Coding<br />
197 Standard, which can be referenced in full here:<br />
199 <a class="link" href="http://www.gnu.org/prep/standards/standards.html#Formatting" target="_top">http://www.gnu.org/prep/standards/standards.html#Formatting</a><br />
201 The rest of this is also interesting reading, but skip the "Design<br />
204 The GCC coding conventions are here, and are also useful:<br />
205 <a class="link" href="http://gcc.gnu.org/codingconventions.html" target="_top">http://gcc.gnu.org/codingconventions.html</a><br />
207 In addition, because it doesn't seem to be stated explicitly anywhere<br />
208 else, there is an 80 column source limit.<br />
210 <code class="filename">ChangeLog</code> entries for member functions should use the<br />
211 classname::member function name syntax as follows:<br />
213 <code class="code"><br />
214 1999-04-15 Dennis Ritchie <dr@att.com><br />
216 * src/basic_file.cc (__basic_file::open): Fix thinko in<br />
217 _G_HAVE_IO_FILE_OPEN bits.<br />
220 Notable areas of divergence from what may be previous local practice<br />
221 (particularly for GNU C) include:<br />
223 01. Pointers and references<br />
224 <code class="code"><br />
225 char* p = "flop";<br />
226 char& c = *p;<br />
228 char *p = "flop"; // wrong<br />
229 char &c = *p; // wrong<br />
232 Reason: In C++, definitions are mixed with executable code. Here,<br />
233 <code class="code">p</code> is being initialized, not <code class="code">*p</code>. This is near-universal<br />
234 practice among C++ programmers; it is normal for C hackers<br />
235 to switch spontaneously as they gain experience.<br />
237 02. Operator names and parentheses<br />
238 <code class="code"><br />
239 operator==(type)<br />
241 operator == (type) // wrong<br />
244 Reason: The <code class="code">==</code> is part of the function name. Separating<br />
245 it makes the declaration look like an expression.<br />
247 03. Function names and parentheses<br />
248 <code class="code"><br />
251 void mangle () // wrong<br />
254 Reason: no space before parentheses (except after a control-flow<br />
255 keyword) is near-universal practice for C++. It identifies the<br />
256 parentheses as the function-call operator or declarator, as<br />
257 opposed to an expression or other overloaded use of parentheses.<br />
259 04. Template function indentation<br />
260 <code class="code"><br />
261 template<typename T><br />
263 template_function(args)<br />
266 template<class T><br />
267 void template_function(args) {};<br />
270 Reason: In class definitions, without indentation whitespace is<br />
271 needed both above and below the declaration to distinguish<br />
272 it visually from other members. (Also, re: "typename"<br />
273 rather than "class".) <code class="code">T</code> often could be <code class="code">int</code>, which is<br />
274 not a class. ("class", here, is an anachronism.)<br />
276 05. Template class indentation<br />
277 <code class="code"><br />
278 template<typename _CharT, typename _Traits><br />
279 class basic_ios : public ios_base<br />
285 template<class _CharT, class _Traits><br />
286 class basic_ios : public ios_base<br />
292 template<class _CharT, class _Traits><br />
293 class basic_ios : public ios_base<br />
300 06. Enumerators<br />
301 <code class="code"><br />
304 space = _ISspace,<br />
305 print = _ISprint,<br />
306 cntrl = _IScntrl<br />
309 enum { space = _ISspace, print = _ISprint, cntrl = _IScntrl };<br />
312 07. Member initialization lists<br />
313 All one line, separate from class name.<br />
315 <code class="code"><br />
316 gribble::gribble()<br />
317 : _M_private_data(0), _M_more_stuff(0), _M_helper(0)<br />
320 gribble::gribble() : _M_private_data(0), _M_more_stuff(0), _M_helper(0)<br />
324 08. Try/Catch blocks<br />
325 <code class="code"><br />
342 09. Member functions declarations and definitions<br />
343 Keywords such as extern, static, export, explicit, inline, etc<br />
344 go on the line above the function name. Thus<br />
346 <code class="code"><br />
350 virtual int foo()<br />
353 Reason: GNU coding conventions dictate return types for functions<br />
354 are on a separate line than the function name and parameter list<br />
355 for definitions. For C++, where we have member functions that can<br />
356 be either inline definitions or declarations, keeping to this<br />
357 standard allows all member function names for a given class to be<br />
358 aligned to the same margin, increasing readability.<br />
361 10. Invocation of member functions with "this->"<br />
362 For non-uglified names, use <code class="code">this->name</code> to call the function.<br />
364 <code class="code"><br />
365 this->sync()<br />
370 Reason: Koenig lookup.<br />
373 <code class="code"><br />
376 blah blah blah;<br />
377 } // namespace std<br />
381 namespace std {<br />
382 blah blah blah;<br />
383 } // namespace std<br />
386 12. Spacing under protected and private in class declarations:<br />
387 space above, none below<br />
390 <code class="code"><br />
400 13. Spacing WRT return statements.<br />
401 no extra spacing before returns, no parenthesis<br />
404 <code class="code"><br />
416 return (__ret);<br />
420 14. Location of global variables.<br />
421 All global variables of class type, whether in the "user visible"<br />
422 space (e.g., <code class="code">cin</code>) or the implementation namespace, must be defined<br />
423 as a character array with the appropriate alignment and then later<br />
424 re-initialized to the correct value.<br />
426 This is due to startup issues on certain platforms, such as AIX.<br />
427 For more explanation and examples, see <code class="filename">src/globals.cc</code>. All such<br />
428 variables should be contained in that file, for simplicity.<br />
430 15. Exception abstractions<br />
431 Use the exception abstractions found in <code class="filename">functexcept.h</code>, which allow<br />
432 C++ programmers to use this library with <code class="literal">-fno-exceptions</code>. (Even if<br />
433 that is rarely advisable, it's a necessary evil for backwards<br />
434 compatibility.)<br />
436 16. Exception error messages<br />
437 All start with the name of the function where the exception is<br />
438 thrown, and then (optional) descriptive text is added. Example:<br />
440 <code class="code"><br />
441 __throw_logic_error(__N("basic_string::_S_construct NULL not valid"));<br />
444 Reason: The verbose terminate handler prints out <code class="code">exception::what()</code>,<br />
445 as well as the typeinfo for the thrown exception. As this is the<br />
446 default terminate handler, by putting location info into the<br />
447 exception string, a very useful error message is printed out for<br />
448 uncaught exceptions. So useful, in fact, that non-programmers can<br />
449 give useful error messages, and programmers can intelligently<br />
450 speculate what went wrong without even using a debugger.<br />
452 17. The doxygen style guide to comments is a separate document,<br />
455 The library currently has a mixture of GNU-C and modern C++ coding<br />
456 styles. The GNU C usages will be combed out gradually.<br />
460 For nonstandard names appearing in Standard headers, we are constrained<br />
461 to use names that begin with underscores. This is called "uglification".<br />
462 The convention is:<br />
464 Local and argument names: <code class="literal">__[a-z].*</code><br />
466 Examples: <code class="code">__count __ix __s1</code><br />
468 Type names and template formal-argument names: <code class="literal">_[A-Z][^_].*</code><br />
470 Examples: <code class="code">_Helper _CharT _N</code><br />
472 Member data and function names: <code class="literal">_M_.*</code><br />
474 Examples: <code class="code">_M_num_elements _M_initialize ()</code><br />
476 Static data members, constants, and enumerations: <code class="literal">_S_.*</code><br />
478 Examples: <code class="code">_S_max_elements _S_default_value</code><br />
480 Don't use names in the same scope that differ only in the prefix,<br />
481 e.g. _S_top and _M_top. See BADNAMES for a list of forbidden names.<br />
482 (The most tempting of these seem to be and "_T" and "__sz".)<br />
484 Names must never have "__" internally; it would confuse name<br />
485 unmanglers on some targets. Also, never use "__[0-9]", same reason.<br />
487 --------------------------<br />
490 <code class="code"><br />
492 #ifndef _HEADER_<br />
493 #define _HEADER_ 1<br />
500 gribble() throw();<br />
502 gribble(const gribble&);<br />
505 gribble(int __howmany);<br />
508 operator=(const gribble&);<br />
511 ~gribble() throw ();<br />
513 // Start with a capital letter, end with a period.<br />
515 public_member(const char* __arg) const;<br />
517 // In-class function definitions should be restricted to one-liners.<br />
519 one_line() { return 0 }<br />
522 two_lines(const char* arg)<br />
523 { return strchr(arg, 'a'); }<br />
526 three_lines(); // inline, but defined below.<br />
528 // Note indentation.<br />
529 template<typename _Formal_argument><br />
531 public_template() const throw();<br />
533 template<typename _Iterator><br />
535 other_template();<br />
540 int _M_private_data;<br />
541 int _M_more_stuff;<br />
542 _Helper* _M_helper;<br />
543 int _M_private_function();<br />
552 _S_initialize_library();<br />
555 // More-or-less-standard language features described by lack, not presence.<br />
556 # ifndef _G_NO_LONGLONG<br />
557 extern long long _G_global_with_a_good_long_name; // avoid globals!<br />
560 // Avoid in-class inline definitions, define separately;<br />
561 // likewise for member class definitions:<br />
563 gribble::public_member() const<br />
564 { int __local = 0; return __local; }<br />
566 class gribble::_Helper<br />
570 friend class gribble;<br />
574 // Names beginning with "__": only for arguments and<br />
575 // local variables; never use "__" in a type name, or<br />
576 // within any name; never use "__[0-9]".<br />
578 #endif /* _HEADER_ */<br />
583 template<typename T> // notice: "typename", not "class", no space<br />
584 long_return_value_type<with_many, args><br />
585 function_name(char* pointer, // "char *pointer" is wrong.<br />
586 char* argument,<br />
587 const Reference& ref)<br />
589 // int a_local; /* wrong; see below. */<br />
595 int a_local = 0; // declare variable at first use.<br />
597 // char a, b, *p; /* wrong */<br />
599 char b = a + 1;<br />
600 char* c = "abc"; // each variable goes on its own line, always.<br />
602 // except maybe here...<br />
603 for (unsigned i = 0, mask = 1; mask; ++i, mask <<= 1) {<br />
608 gribble::gribble()<br />
609 : _M_private_data(0), _M_more_stuff(0), _M_helper(0)<br />
613 gribble::three_lines()<br />
615 // doesn't fit in one line.<br />
617 } // namespace std<br />
619 </p></div></div></div><div class="navfooter"><hr /><table width="100%" summary="Navigation footer"><tr><td width="40%" align="left"><a accesskey="p" href="source_organization.html">Prev</a> </td><td width="20%" align="center"><a accesskey="u" href="appendix_contributing.html">Up</a></td><td width="40%" align="right"> <a accesskey="n" href="source_design_notes.html">Next</a></td></tr><tr><td width="40%" align="left" valign="top">Directory Layout and Source Conventions </td><td width="20%" align="center"><a accesskey="h" href="../index.html">Home</a></td><td width="40%" align="right" valign="top"> Design Notes</td></tr></table></div></body></html>