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<?xml version="1.0" encoding="UTF-8" standalone="no"?>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd">
<html xmlns="http://www.w3.org/1999/xhtml"><head><title>Coding Style</title><meta name="generator" content="DocBook XSL-NS Stylesheets V1.76.1"/><meta name="keywords" content=" ISO C++ , library "/><link rel="home" href="../spine.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 align="left"><a accesskey="p" href="source_organization.html">Prev</a> </td><th width="60%" align="center">Appendix A.
Contributing
</th><td align="right"> <a accesskey="n" href="source_design_notes.html">Next</a></td></tr></table><hr/></div><div class="section" title="Coding Style"><div class="titlepage"><div><div><h2 class="title"><a id="contrib.coding_style"/>Coding Style</h2></div></div></div><p>
</p><div class="section" title="Bad Identifiers"><div class="titlepage"><div><div><h3 class="title"><a id="coding_style.bad_identifiers"/>Bad Identifiers</h3></div></div></div><p>
Identifiers that conflict and should be avoided.
</p><div class="literallayout"><p><br/>
This is the list of names <span class="quote">“<span class="quote">reserved to the<br/>
implementation</span>”</span> that have been claimed by certain<br/>
compilers and system headers of interest, and should not be used<br/>
in the library. It will grow, of course. We generally are<br/>
interested in names that are not all-caps, except for those like<br/>
"_T"<br/>
<br/>
For Solaris:<br/>
_B<br/>
_C<br/>
_L<br/>
_N<br/>
_P<br/>
_S<br/>
_U<br/>
_X<br/>
_E1<br/>
..<br/>
_E24<br/>
<br/>
Irix adds:<br/>
_A<br/>
_G<br/>
<br/>
MS adds:<br/>
_T<br/>
<br/>
BSD adds:<br/>
__used<br/>
__unused<br/>
__inline<br/>
_Complex<br/>
__istype<br/>
__maskrune<br/>
__tolower<br/>
__toupper<br/>
__wchar_t<br/>
__wint_t<br/>
_res<br/>
_res_ext<br/>
__tg_*<br/>
<br/>
SPU adds:<br/>
__ea<br/>
<br/>
For GCC:<br/>
<br/>
[Note that this list is out of date. It applies to the old<br/>
name-mangling; in G++ 3.0 and higher a different name-mangling is<br/>
used. In addition, many of the bugs relating to G++ interpreting<br/>
these names as operators have been fixed.]<br/>
<br/>
The full set of __* identifiers (combined from gcc/cp/lex.c and<br/>
gcc/cplus-dem.c) that are either old or new, but are definitely<br/>
recognized by the demangler, is:<br/>
<br/>
__aa<br/>
__aad<br/>
__ad<br/>
__addr<br/>
__adv<br/>
__aer<br/>
__als<br/>
__alshift<br/>
__amd<br/>
__ami<br/>
__aml<br/>
__amu<br/>
__aor<br/>
__apl<br/>
__array<br/>
__ars<br/>
__arshift<br/>
__as<br/>
__bit_and<br/>
__bit_ior<br/>
__bit_not<br/>
__bit_xor<br/>
__call<br/>
__cl<br/>
__cm<br/>
__cn<br/>
__co<br/>
__component<br/>
__compound<br/>
__cond<br/>
__convert<br/>
__delete<br/>
__dl<br/>
__dv<br/>
__eq<br/>
__er<br/>
__ge<br/>
__gt<br/>
__indirect<br/>
__le<br/>
__ls<br/>
__lt<br/>
__max<br/>
__md<br/>
__method_call<br/>
__mi<br/>
__min<br/>
__minus<br/>
__ml<br/>
__mm<br/>
__mn<br/>
__mult<br/>
__mx<br/>
__ne<br/>
__negate<br/>
__new<br/>
__nop<br/>
__nt<br/>
__nw<br/>
__oo<br/>
__op<br/>
__or<br/>
__pl<br/>
__plus<br/>
__postdecrement<br/>
__postincrement<br/>
__pp<br/>
__pt<br/>
__rf<br/>
__rm<br/>
__rs<br/>
__sz<br/>
__trunc_div<br/>
__trunc_mod<br/>
__truth_andif<br/>
__truth_not<br/>
__truth_orif<br/>
__vc<br/>
__vd<br/>
__vn<br/>
<br/>
SGI badnames:<br/>
__builtin_alloca<br/>
__builtin_fsqrt<br/>
__builtin_sqrt<br/>
__builtin_fabs<br/>
__builtin_dabs<br/>
__builtin_cast_f2i<br/>
__builtin_cast_i2f<br/>
__builtin_cast_d2ll<br/>
__builtin_cast_ll2d<br/>
__builtin_copy_dhi2i<br/>
__builtin_copy_i2dhi<br/>
__builtin_copy_dlo2i<br/>
__builtin_copy_i2dlo<br/>
__add_and_fetch<br/>
__sub_and_fetch<br/>
__or_and_fetch<br/>
__xor_and_fetch<br/>
__and_and_fetch<br/>
__nand_and_fetch<br/>
__mpy_and_fetch<br/>
__min_and_fetch<br/>
__max_and_fetch<br/>
__fetch_and_add<br/>
__fetch_and_sub<br/>
__fetch_and_or<br/>
__fetch_and_xor<br/>
__fetch_and_and<br/>
__fetch_and_nand<br/>
__fetch_and_mpy<br/>
__fetch_and_min<br/>
__fetch_and_max<br/>
__lock_test_and_set<br/>
__lock_release<br/>
__lock_acquire<br/>
__compare_and_swap<br/>
__synchronize<br/>
__high_multiply<br/>
__unix<br/>
__sgi<br/>
__linux__<br/>
__i386__<br/>
__i486__<br/>
__cplusplus<br/>
__embedded_cplusplus<br/>
// long double conversion members mangled as __opr<br/>
// http://gcc.gnu.org/ml/libstdc++/1999-q4/msg00060.html<br/>
__opr<br/>
</p></div></div><div class="section" title="By Example"><div class="titlepage"><div><div><h3 class="title"><a id="coding_style.example"/>By Example</h3></div></div></div><div class="literallayout"><p><br/>
This library is written to appropriate C++ coding standards. As such,<br/>
it is intended to precede the recommendations of the GNU Coding<br/>
Standard, which can be referenced in full here:<br/>
<br/>
<a class="link" href="http://www.gnu.org/prep/standards/standards.html#Formatting">http://www.gnu.org/prep/standards/standards.html#Formatting</a><br/>
<br/>
The rest of this is also interesting reading, but skip the "Design<br/>
Advice" part.<br/>
<br/>
The GCC coding conventions are here, and are also useful:<br/>
<a class="link" href="http://gcc.gnu.org/codingconventions.html">http://gcc.gnu.org/codingconventions.html</a><br/>
<br/>
In addition, because it doesn't seem to be stated explicitly anywhere<br/>
else, there is an 80 column source limit.<br/>
<br/>
<code class="filename">ChangeLog</code> entries for member functions should use the<br/>
classname::member function name syntax as follows:<br/>
<br/>
<code class="code"><br/>
1999-04-15 Dennis Ritchie <dr@att.com><br/>
<br/>
* src/basic_file.cc (__basic_file::open): Fix thinko in<br/>
_G_HAVE_IO_FILE_OPEN bits.<br/>
</code><br/>
<br/>
Notable areas of divergence from what may be previous local practice<br/>
(particularly for GNU C) include:<br/>
<br/>
01. Pointers and references<br/>
<code class="code"><br/>
char* p = "flop";<br/>
char& c = *p;<br/>
-NOT-<br/>
char *p = "flop"; // wrong<br/>
char &c = *p; // wrong<br/>
</code><br/>
<br/>
Reason: In C++, definitions are mixed with executable code. Here,<br/>
<code class="code">p</code> is being initialized, not <code class="code">*p</code>. This is near-universal<br/>
practice among C++ programmers; it is normal for C hackers<br/>
to switch spontaneously as they gain experience.<br/>
<br/>
02. Operator names and parentheses<br/>
<code class="code"><br/>
operator==(type)<br/>
-NOT-<br/>
operator == (type) // wrong<br/>
</code><br/>
<br/>
Reason: The <code class="code">==</code> is part of the function name. Separating<br/>
it makes the declaration look like an expression.<br/>
<br/>
03. Function names and parentheses<br/>
<code class="code"><br/>
void mangle()<br/>
-NOT-<br/>
void mangle () // wrong<br/>
</code><br/>
<br/>
Reason: no space before parentheses (except after a control-flow<br/>
keyword) is near-universal practice for C++. It identifies the<br/>
parentheses as the function-call operator or declarator, as<br/>
opposed to an expression or other overloaded use of parentheses.<br/>
<br/>
04. Template function indentation<br/>
<code class="code"><br/>
template<typename T><br/>
void<br/>
template_function(args)<br/>
{ }<br/>
-NOT-<br/>
template<class T><br/>
void template_function(args) {};<br/>
</code><br/>
<br/>
Reason: In class definitions, without indentation whitespace is<br/>
needed both above and below the declaration to distinguish<br/>
it visually from other members. (Also, re: "typename"<br/>
rather than "class".) <code class="code">T</code> often could be <code class="code">int</code>, which is<br/>
not a class. ("class", here, is an anachronism.)<br/>
<br/>
05. Template class indentation<br/>
<code class="code"><br/>
template<typename _CharT, typename _Traits><br/>
class basic_ios : public ios_base<br/>
{<br/>
public:<br/>
// Types:<br/>
};<br/>
-NOT-<br/>
template<class _CharT, class _Traits><br/>
class basic_ios : public ios_base<br/>
{<br/>
public:<br/>
// Types:<br/>
};<br/>
-NOT-<br/>
template<class _CharT, class _Traits><br/>
class basic_ios : public ios_base<br/>
{<br/>
public:<br/>
// Types:<br/>
};<br/>
</code><br/>
<br/>
06. Enumerators<br/>
<code class="code"><br/>
enum<br/>
{<br/>
space = _ISspace,<br/>
print = _ISprint,<br/>
cntrl = _IScntrl<br/>
};<br/>
-NOT-<br/>
enum { space = _ISspace, print = _ISprint, cntrl = _IScntrl };<br/>
</code><br/>
<br/>
07. Member initialization lists<br/>
All one line, separate from class name.<br/>
<br/>
<code class="code"><br/>
gribble::gribble()<br/>
: _M_private_data(0), _M_more_stuff(0), _M_helper(0)<br/>
{ }<br/>
-NOT-<br/>
gribble::gribble() : _M_private_data(0), _M_more_stuff(0), _M_helper(0)<br/>
{ }<br/>
</code><br/>
<br/>
08. Try/Catch blocks<br/>
<code class="code"><br/>
try<br/>
{<br/>
//<br/>
}<br/>
catch (...)<br/>
{<br/>
//<br/>
}<br/>
-NOT-<br/>
try {<br/>
//<br/>
} catch(...) {<br/>
//<br/>
}<br/>
</code><br/>
<br/>
09. Member functions declarations and definitions<br/>
Keywords such as extern, static, export, explicit, inline, etc<br/>
go on the line above the function name. Thus<br/>
<br/>
<code class="code"><br/>
virtual int<br/>
foo()<br/>
-NOT-<br/>
virtual int foo()<br/>
</code><br/>
<br/>
Reason: GNU coding conventions dictate return types for functions<br/>
are on a separate line than the function name and parameter list<br/>
for definitions. For C++, where we have member functions that can<br/>
be either inline definitions or declarations, keeping to this<br/>
standard allows all member function names for a given class to be<br/>
aligned to the same margin, increasing readability.<br/>
<br/>
<br/>
10. Invocation of member functions with "this->"<br/>
For non-uglified names, use <code class="code">this->name</code> to call the function.<br/>
<br/>
<code class="code"><br/>
this->sync()<br/>
-NOT-<br/>
sync()<br/>
</code><br/>
<br/>
Reason: Koenig lookup.<br/>
<br/>
11. Namespaces<br/>
<code class="code"><br/>
namespace std<br/>
{<br/>
blah blah blah;<br/>
} // namespace std<br/>
<br/>
-NOT-<br/>
<br/>
namespace std {<br/>
blah blah blah;<br/>
} // namespace std<br/>
</code><br/>
<br/>
12. Spacing under protected and private in class declarations:<br/>
space above, none below<br/>
i.e.<br/>
<br/>
<code class="code"><br/>
public:<br/>
int foo;<br/>
<br/>
-NOT-<br/>
public:<br/>
<br/>
int foo;<br/>
</code><br/>
<br/>
13. Spacing WRT return statements.<br/>
no extra spacing before returns, no parenthesis<br/>
i.e.<br/>
<br/>
<code class="code"><br/>
}<br/>
return __ret;<br/>
<br/>
-NOT-<br/>
}<br/>
<br/>
return __ret;<br/>
<br/>
-NOT-<br/>
<br/>
}<br/>
return (__ret);<br/>
</code><br/>
<br/>
<br/>
14. Location of global variables.<br/>
All global variables of class type, whether in the "user visible"<br/>
space (e.g., <code class="code">cin</code>) or the implementation namespace, must be defined<br/>
as a character array with the appropriate alignment and then later<br/>
re-initialized to the correct value.<br/>
<br/>
This is due to startup issues on certain platforms, such as AIX.<br/>
For more explanation and examples, see <code class="filename">src/globals.cc</code>. All such<br/>
variables should be contained in that file, for simplicity.<br/>
<br/>
15. Exception abstractions<br/>
Use the exception abstractions found in <code class="filename">functexcept.h</code>, which allow<br/>
C++ programmers to use this library with <code class="literal">-fno-exceptions</code>. (Even if<br/>
that is rarely advisable, it's a necessary evil for backwards<br/>
compatibility.)<br/>
<br/>
16. Exception error messages<br/>
All start with the name of the function where the exception is<br/>
thrown, and then (optional) descriptive text is added. Example:<br/>
<br/>
<code class="code"><br/>
__throw_logic_error(__N("basic_string::_S_construct NULL not valid"));<br/>
</code><br/>
<br/>
Reason: The verbose terminate handler prints out <code class="code">exception::what()</code>,<br/>
as well as the typeinfo for the thrown exception. As this is the<br/>
default terminate handler, by putting location info into the<br/>
exception string, a very useful error message is printed out for<br/>
uncaught exceptions. So useful, in fact, that non-programmers can<br/>
give useful error messages, and programmers can intelligently<br/>
speculate what went wrong without even using a debugger.<br/>
<br/>
17. The doxygen style guide to comments is a separate document,<br/>
see index.<br/>
<br/>
The library currently has a mixture of GNU-C and modern C++ coding<br/>
styles. The GNU C usages will be combed out gradually.<br/>
<br/>
Name patterns:<br/>
<br/>
For nonstandard names appearing in Standard headers, we are constrained<br/>
to use names that begin with underscores. This is called "uglification".<br/>
The convention is:<br/>
<br/>
Local and argument names: <code class="literal">__[a-z].*</code><br/>
<br/>
Examples: <code class="code">__count __ix __s1</code><br/>
<br/>
Type names and template formal-argument names: <code class="literal">_[A-Z][^_].*</code><br/>
<br/>
Examples: <code class="code">_Helper _CharT _N</code><br/>
<br/>
Member data and function names: <code class="literal">_M_.*</code><br/>
<br/>
Examples: <code class="code">_M_num_elements _M_initialize ()</code><br/>
<br/>
Static data members, constants, and enumerations: <code class="literal">_S_.*</code><br/>
<br/>
Examples: <code class="code">_S_max_elements _S_default_value</code><br/>
<br/>
Don't use names in the same scope that differ only in the prefix,<br/>
e.g. _S_top and _M_top. See BADNAMES for a list of forbidden names.<br/>
(The most tempting of these seem to be and "_T" and "__sz".)<br/>
<br/>
Names must never have "__" internally; it would confuse name<br/>
unmanglers on some targets. Also, never use "__[0-9]", same reason.<br/>
<br/>
--------------------------<br/>
<br/>
[BY EXAMPLE]<br/>
<code class="code"><br/>
<br/>
#ifndef _HEADER_<br/>
#define _HEADER_ 1<br/>
<br/>
namespace std<br/>
{<br/>
class gribble<br/>
{<br/>
public:<br/>
gribble() throw();<br/>
<br/>
gribble(const gribble&);<br/>
<br/>
explicit<br/>
gribble(int __howmany);<br/>
<br/>
gribble&<br/>
operator=(const gribble&);<br/>
<br/>
virtual<br/>
~gribble() throw ();<br/>
<br/>
// Start with a capital letter, end with a period.<br/>
inline void<br/>
public_member(const char* __arg) const;<br/>
<br/>
// In-class function definitions should be restricted to one-liners.<br/>
int<br/>
one_line() { return 0 }<br/>
<br/>
int<br/>
two_lines(const char* arg)<br/>
{ return strchr(arg, 'a'); }<br/>
<br/>
inline int<br/>
three_lines(); // inline, but defined below.<br/>
<br/>
// Note indentation.<br/>
template<typename _Formal_argument><br/>
void<br/>
public_template() const throw();<br/>
<br/>
template<typename _Iterator><br/>
void<br/>
other_template();<br/>
<br/>
private:<br/>
class _Helper;<br/>
<br/>
int _M_private_data;<br/>
int _M_more_stuff;<br/>
_Helper* _M_helper;<br/>
int _M_private_function();<br/>
<br/>
enum _Enum<br/>
{<br/>
_S_one,<br/>
_S_two<br/>
};<br/>
<br/>
static void<br/>
_S_initialize_library();<br/>
};<br/>
<br/>
// More-or-less-standard language features described by lack, not presence.<br/>
# ifndef _G_NO_LONGLONG<br/>
extern long long _G_global_with_a_good_long_name; // avoid globals!<br/>
# endif<br/>
<br/>
// Avoid in-class inline definitions, define separately;<br/>
// likewise for member class definitions:<br/>
inline int<br/>
gribble::public_member() const<br/>
{ int __local = 0; return __local; }<br/>
<br/>
class gribble::_Helper<br/>
{<br/>
int _M_stuff;<br/>
<br/>
friend class gribble;<br/>
};<br/>
}<br/>
<br/>
// Names beginning with "__": only for arguments and<br/>
// local variables; never use "__" in a type name, or<br/>
// within any name; never use "__[0-9]".<br/>
<br/>
#endif /* _HEADER_ */<br/>
<br/>
<br/>
namespace std<br/>
{<br/>
template<typename T> // notice: "typename", not "class", no space<br/>
long_return_value_type<with_many, args><br/>
function_name(char* pointer, // "char *pointer" is wrong.<br/>
char* argument,<br/>
const Reference& ref)<br/>
{<br/>
// int a_local; /* wrong; see below. */<br/>
if (test)<br/>
{<br/>
nested code<br/>
}<br/>
<br/>
int a_local = 0; // declare variable at first use.<br/>
<br/>
// char a, b, *p; /* wrong */<br/>
char a = 'a';<br/>
char b = a + 1;<br/>
char* c = "abc"; // each variable goes on its own line, always.<br/>
<br/>
// except maybe here...<br/>
for (unsigned i = 0, mask = 1; mask; ++i, mask <<= 1) {<br/>
// ...<br/>
}<br/>
}<br/>
<br/>
gribble::gribble()<br/>
: _M_private_data(0), _M_more_stuff(0), _M_helper(0)<br/>
{ }<br/>
<br/>
int<br/>
gribble::three_lines()<br/>
{<br/>
// doesn't fit in one line.<br/>
}<br/>
} // namespace std<br/>
</code><br/>
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