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Misha Brukmanc1449e62008-12-10 23:07:02 +0000[diff] [blame]6 <title>LLVM Coding Standards</title>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]7</head>
8<body>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]9
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]10<div class="doc_title">
Misha Brukmanc1449e62008-12-10 23:07:02 +0000[diff] [blame]11 LLVM Coding Standards
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]12</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]13
14<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner7ae36bb2001-07-23 20:40:41 +0000[diff] [blame]16 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]17 <ol>
18 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]19 <ol>
20 <li><a href="#scf_commenting">Commenting</a></li>
21 <li><a href="#scf_commentformat">Comment Formatting</a></li>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]22 <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]23 <li><a href="#scf_codewidth">Source Code Width</a></li>
24 <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
25 <li><a href="#scf_indentation">Indent Code Consistently</a></li>
26 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]27 <li><a href="#compilerissues">Compiler Issues</a>
28 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]29 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
30 Errors</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]31 <li><a href="#ci_portable_code">Write Portable Code</a></li>
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]32 <li><a href="#ci_class_struct">Use of class/struct Keywords</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]33 </ol></li>
34 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]35 <li><a href="#styleissues">Style Issues</a>
36 <ol>
37 <li><a href="#macro">The High Level Issues</a>
38 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]39 <li><a href="#hl_module">A Public Header File <b>is</b> a
40 Module</a></li>
41 <li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
42 <li><a href="#hl_privateheaders">Keep "internal" Headers
43 Private</a></li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]44 <li><a href="#ll_iostream"><tt>#include &lt;iostream&gt;</tt> is
45 <em>forbidden</em></a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]46 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]47 <li><a href="#micro">The Low Level Issues</a>
48 <ol>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]49 <li><a href="#ll_assert">Assert Liberally</a></li>
50 <li><a href="#ll_ns_std">Do not use 'using namespace std'</a></li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]51 <li><a href="#ll_virtual_anch">Provide a virtual method anchor for
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]52 classes in headers</a></li>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]53 <li><a href="#ll_preincrement">Prefer Preincrement</a></li>
54 <li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]55 </ol></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]56 </ol></li>
57 <li><a href="#seealso">See Also</a></li>
58</ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]59
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]60<div class="doc_author">
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]61 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
62 <a href="mailto:void@nondot.org">Bill Wendling</a></p>
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]63</div>
64
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]65
66<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]67<div class="doc_section">
68 <a name="introduction">Introduction</a>
69</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]70<!-- *********************************************************************** -->
71
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]72<div class="doc_text">
73
74<p>This document attempts to describe a few coding standards that are being used
75in the LLVM source tree. Although no coding standards should be regarded as
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]76absolute requirements to be followed in all instances, coding standards can be
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]77useful.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]78
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]79<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]80issues such as brace placement and space usage. For issues like this, follow
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]81the golden rule:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]82
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]83<blockquote>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]84
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]85<p><b><a name="goldenrule">If you are adding a significant body of source to a
86project, feel free to use whatever style you are most comfortable with. If you
87are extending, enhancing, or bug fixing already implemented code, use the style
88that is already being used so that the source is uniform and easy to
89follow.</a></b></p>
90
91</blockquote>
92
93<p>The ultimate goal of these guidelines is the increase readability and
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]94maintainability of our common source base. If you have suggestions for topics to
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]95be included, please mail them to <a
96href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]97
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]98</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]99
100<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]101<div class="doc_section">
102 <a name="mechanicalissues">Mechanical Source Issues</a>
103</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]104<!-- *********************************************************************** -->
105
106<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]107<div class="doc_subsection">
108 <a name="sourceformating">Source Code Formatting</a>
109</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]110
111<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]112<div class="doc_subsubsection">
113 <a name="scf_commenting">Commenting</a>
114</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]115
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]116<div class="doc_text">
117
118<p>Comments are one critical part of readability and maintainability. Everyone
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]119knows they should comment, so should you. Although we all should probably
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]120comment our code more than we do, there are a few very critical places that
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]121documentation is very useful:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]122
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]123<b>File Headers</b>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]124
Reid Spencer669ed452007-07-09 08:04:31 +0000[diff] [blame]125<p>Every source file should have a header on it that describes the basic
126purpose of the file. If a file does not have a header, it should not be
127checked into Subversion. Most source trees will probably have a standard
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]128file header format. The standard format for the LLVM source tree looks like
129this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]130
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]131<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]132<pre>
Chris Lattnerc49fcd12003-10-13 14:58:11 +0000[diff] [blame]133//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Misha Brukman98117cd2009-01-02 16:58:42 +0000[diff] [blame]134//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]135// The LLVM Compiler Infrastructure
136//
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]137// This file is distributed under the University of Illinois Open Source
138// License. See LICENSE.TXT for details.
Misha Brukman98117cd2009-01-02 16:58:42 +0000[diff] [blame]139//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]140//===----------------------------------------------------------------------===//
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]141//
142// This file contains the declaration of the Instruction class, which is the
143// base class for all of the VM instructions.
144//
145//===----------------------------------------------------------------------===//
146</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]147</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]148
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]149<p>A few things to note about this particular format: The "<tt>-*- C++
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]150-*-</tt>" string on the first line is there to tell Emacs that the source file
Misha Brukman69c58892004-07-28 22:37:57 +0000[diff] [blame]151is a C++ file, not a C file (Emacs assumes .h files are C files by default).
152Note that this tag is not necessary in .cpp files. The name of the file is also
153on the first line, along with a very short description of the purpose of the
154file. This is important when printing out code and flipping though lots of
155pages.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]156
Chris Lattnerab2b10c2007-12-29 19:56:08 +0000[diff] [blame]157<p>The next section in the file is a concise note that defines the license
158that the file is released under. This makes it perfectly clear what terms the
159source code can be distributed under and should not be modified in any way.</p>
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]160
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]161<p>The main body of the description does not have to be very long in most cases.
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]162Here it's only two lines. If an algorithm is being implemented or something
163tricky is going on, a reference to the paper where it is published should be
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]164included, as well as any notes or "gotchas" in the code to watch out for.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]165
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]166<b>Class overviews</b>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]167
Jim Laskeyf55914a2006-07-31 20:18:49 +0000[diff] [blame]168<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]169a class definition should have a comment block that explains what the class is
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]170used for... if it's not obvious. If it's so completely obvious your grandma
171could figure it out, it's probably safe to leave it out. Naming classes
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]172something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]173
174
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]175<b>Method information</b>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]176
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]177<p>Methods defined in a class (as well as any global functions) should also be
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]178documented properly. A quick note about what it does any a description of the
179borderline behaviour is all that is necessary here (unless something
180particularly tricky or insideous is going on). The hope is that people can
181figure out how to use your interfaces without reading the code itself... that is
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]182the goal metric.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]183
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]184<p>Good things to talk about here are what happens when something unexpected
185happens: does the method return null? Abort? Format your hard disk?</p>
186
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]187</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]188
189<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]190<div class="doc_subsubsection">
191 <a name="scf_commentformat">Comment Formatting</a>
192</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]193
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]194<div class="doc_text">
195
196<p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]197require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]198when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]199
200<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]201 <li>When writing a C code: Obviously if you are writing C code, use C style
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]202 comments.</li>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]203 <li>When writing a header file that may be <tt>#include</tt>d by a C source
204 file.</li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]205 <li>When writing a source file that is used by a tool that only accepts C
206 style comments.</li>
207</ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]208
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]209<p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
210These nest properly and are better behaved in general than C style comments.</p>
211
212</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]213
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]214<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]215<div class="doc_subsubsection">
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]216 <a name="scf_includes"><tt>#include</tt> Style</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]217</div>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]218
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]219<div class="doc_text">
220
221<p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]222include guards if working on a header file), the <a
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]223href="#hl_dontinclude">minimal</a> list of <tt>#include</tt>s required by the
224file should be listed. We prefer these <tt>#include</tt>s to be listed in this
225order:</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]226
227<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]228 <li><a href="#mmheader">Main Module header</a></li>
229 <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]230 <li><tt>llvm/*</tt></li>
231 <li><tt>llvm/Analysis/*</tt></li>
232 <li><tt>llvm/Assembly/*</tt></li>
233 <li><tt>llvm/Bytecode/*</tt></li>
234 <li><tt>llvm/CodeGen/*</tt></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]235 <li>...</li>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]236 <li><tt>Support/*</tt></li>
237 <li><tt>Config/*</tt></li>
238 <li>System <tt>#includes</tt></li>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]239</ol>
240
Nick Lewycky822293a2008-11-29 20:13:25 +0000[diff] [blame]241<p>... and each category should be sorted by name.</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]242
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]243<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]244which implement an interface defined by a .h file. This <tt>#include</tt>
245should always be included <b>first</b> regardless of where it lives on the file
246system. By including a header file first in the .cpp files that implement the
247interfaces, we ensure that the header does not have any hidden dependencies
248which are not explicitly #included in the header, but should be. It is also a
249form of documentation in the .cpp file to indicate where the interfaces it
250implements are defined.</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]251
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]252</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]253
254<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]255<div class="doc_subsubsection">
256 <a name="scf_codewidth">Source Code Width</a>
257</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]258
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]259<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]260
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]261<p>Write your code to fit within 80 columns of text. This helps those of us who
262like to print out code and look at your code in an xterm without resizing
263it.</p>
264
Chris Lattner5822e9e2008-07-08 05:12:37 +0000[diff] [blame]265<p>The longer answer is that there must be some limit to the width of the code
266in order to reasonably allow developers to have multiple files side-by-side in
267windows on a modest display. If you are going to pick a width limit, it is
268somewhat arbitrary but you might as well pick something standard. Going with
26990 columns (for example) instead of 80 columns wouldn't add any significant
270value and would be detrimental to printing out code. Also many other projects
271have standardized on 80 columns, so some people have already configured their
272editors for it (vs something else, like 90 columns).</p>
273
274<p>This is one of many contentious issues in coding standards, but is not up
275for debate.</p>
276
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]277</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]278
279<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]280<div class="doc_subsubsection">
281 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
282</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]283
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]284<div class="doc_text">
285
286<p>In all cases, prefer spaces to tabs in source files. People have different
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]287prefered indentation levels, and different styles of indentation that they
288like... this is fine. What isn't is that different editors/viewers expand tabs
289out to different tab stops. This can cause your code to look completely
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]290unreadable, and it is not worth dealing with.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]291
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]292<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]293style of existing code if your are modifying and extending it. If you like four
294spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
295with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]296makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]297
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]298</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]299
300<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]301<div class="doc_subsubsection">
302 <a name="scf_indentation">Indent Code Consistently</a>
303</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]304
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]305<div class="doc_text">
306
307<p>Okay, your first year of programming you were told that indentation is
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]308important. If you didn't believe and internalize this then, now is the time.
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]309Just do it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]310
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]311</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]312
313
314<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]315<div class="doc_subsection">
316 <a name="compilerissues">Compiler Issues</a>
317</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]318
319
320<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]321<div class="doc_subsubsection">
322 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
323</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]324
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]325<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]326
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]327<p>If your code has compiler warnings in it, something is wrong: you aren't
328casting values correctly, your have "questionable" constructs in your code, or
329you are doing something legitimately wrong. Compiler warnings can cover up
330legitimate errors in output and make dealing with a translation unit
331difficult.</p>
332
333<p>It is not possible to prevent all warnings from all compilers, nor is it
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]334desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
335a good thorough set of warnings, and stick to them. At least in the case of
336<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
337syntax of the code slightly. For example, an warning that annoys me occurs when
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]338I write code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]339
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]340<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]341<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]342if (V = getValue()) {
343 ...
344}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]345</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]346</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]347
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]348<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
349operator, and that I probably mistyped it. In most cases, I haven't, and I
350really don't want the spurious errors. To fix this particular problem, I
351rewrite the code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]352
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]353<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]354<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]355if ((V = getValue())) {
356 ...
357}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]358</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]359</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]360
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]361<p>...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
362be fixed by massaging the code appropriately.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]363
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]364<p>These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall
365-Winline -W -Wwrite-strings -Wno-unused</tt></p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]366
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]367</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]368
369<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]370<div class="doc_subsubsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]371 <a name="ci_portable_code">Write Portable Code</a>
372</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]373
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]374<div class="doc_text">
375
376<p>In almost all cases, it is possible and within reason to write completely
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]377portable code. If there are cases where it isn't possible to write portable
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]378code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]379
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]380<p>In practice, this means that you shouldn't assume much about the host
381compiler, including its support for "high tech" features like partial
Chris Lattner4bd3d7e2009-03-23 04:52:53 +0000[diff] [blame^]382specialization of templates. If these features are used, they should only be
383an implementation detail of a library which has a simple exposed API.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]384
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]385</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]386
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]387<!-- _______________________________________________________________________ -->
388<div class="doc_subsubsection">
389<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
390</div>
391<div class="doc_text">
Misha Brukmanedcc78a2004-10-26 15:45:13 +0000[diff] [blame]392
393<p>In C++, the <tt>class</tt> and <tt>struct</tt> keywords can be used almost
394interchangeably. The only difference is when they are used to declare a class:
395<tt>class</tt> makes all members private by default while <tt>struct</tt> makes
396all members public by default.</p>
397
398<p>Unfortunately, not all compilers follow the rules and some will generate
399different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used to
400declare the symbol. This can lead to problems at link time.</p>
401
402<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
403<b>all</b> members are public, in which case <tt>struct</tt> is allowed.</p>
404
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]405</div>
406
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]407<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]408<div class="doc_section">
409 <a name="styleissues">Style Issues</a>
410</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]411<!-- *********************************************************************** -->
412
413
414<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]415<div class="doc_subsection">
416 <a name="macro">The High Level Issues</a>
417</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]418
419
420<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]421<div class="doc_subsubsection">
422 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
423</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]424
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]425<div class="doc_text">
426
427<p>C++ doesn't do too well in the modularity department. There is no real
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]428encapsulation or data hiding (unless you use expensive protocol classes), but it
429is what we have to work with. When you write a public header file (in the LLVM
430source tree, they live in the top level "include" directory), you are defining a
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]431module of functionality.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]432
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]433<p>Ideally, modules should be completely independent of each other, and their
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]434header files should only include the absolute minimum number of headers
435possible. A module is not just a class, a function, or a namespace: <a
436href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection
437of these</a> that defines an interface. This interface may be several
438functions, classes or data structures, but the important issue is how they work
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]439together.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]440
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]441<p>In general, a module should be implemented with one or more <tt>.cpp</tt>
442files. Each of these <tt>.cpp</tt> files should include the header that defines
443their interface first. This ensure that all of the dependences of the module
444header have been properly added to the module header itself, and are not
445implicit. System headers should be included after user headers for a
446translation unit.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]447
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]448</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]449
450<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]451<div class="doc_subsubsection">
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]452 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]453</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]454
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]455<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]456
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]457<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
458have to, especially in header files.</p>
459
460<p>But wait, sometimes you need to have the definition of a class to use it, or
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]461to inherit from it. In these cases go ahead and <tt>#include</tt> that header
462file. Be aware however that there are many cases where you don't need to have
463the full definition of a class. If you are using a pointer or reference to a
464class, you don't need the header file. If you are simply returning a class
465instance from a prototyped function or method, you don't need it. In fact, for
466most cases, you simply don't need the definition of a class... and not
467<tt>#include</tt>'ing speeds up compilation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]468
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]469<p>It is easy to try to go too overboard on this recommendation, however. You
Chris Lattner5da59b12007-02-10 18:35:31 +0000[diff] [blame]470<b>must</b> include all of the header files that you are using -- you can
471include them either directly
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]472or indirectly (through another header file). To make sure that you don't
473accidently forget to include a header file in your module header, make sure to
474include your module header <b>first</b> in the implementation file (as mentioned
475above). This way there won't be any hidden dependencies that you'll find out
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]476about later...</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]477
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]478</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]479
480<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]481<div class="doc_subsubsection">
482 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
483</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]484
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]485<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]486
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]487<p>Many modules have a complex implementation that causes them to use more than
488one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
489internal communication interface (helper classes, extra functions, etc) in the
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]490public module header file. Don't do this.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]491
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]492<p>If you really need to do something like this, put a private header file in
493the same directory as the source files, and include it locally. This ensures
494that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]495
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]496<p>Note however, that it's okay to put extra implementation methods a public
497class itself... just make them private (or protected), and all is well.</p>
498
499</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]500
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]501<!-- _______________________________________________________________________ -->
502<div class="doc_subsubsection">
503 <a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is forbidden</a>
504</div>
505
506<div class="doc_text">
507
508<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
509hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
510support clients using LLVM libraries as part of larger systems. In particular,
511we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
512the static c'tors are run whenever an application start up that uses the dynamic
513library. There are two problems with this:</p>
514
515<ol>
516 <li>The time to run the static c'tors impacts startup time of
Bill Wendling4f6766d2007-11-06 09:36:34 +0000[diff] [blame]517 applications&mdash;a critical time for GUI apps.</li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]518 <li>The static c'tors cause the app to pull many extra pages of memory off the
Bill Wendling4f6766d2007-11-06 09:36:34 +0000[diff] [blame]519 disk: both the code for the static c'tors in each <tt>.o</tt> file and the
520 small amount of data that gets touched. In addition, touched/dirty pages
521 put more pressure on the VM system on low-memory machines.</li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]522</ol>
523
Matthijs Kooijmaned58a972008-07-30 12:14:10 +0000[diff] [blame]524<p>Note that using the other stream headers (<tt>&lt;sstream&gt;</tt> for
525example) is allowed normally, it is just <tt>&lt;iostream&gt;</tt> that is
526causing problems.</p>
527
Chris Lattner4bd3d7e2009-03-23 04:52:53 +0000[diff] [blame^]528<p>The preferred replacement for stream functionality is the
529<tt>raw_ostream</tt> class (for writing to output streams of various sorts) and
530the MemoryBuffer API (for reading in files).</p>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]531
532</div>
533
534
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]535<!-- ======================================================================= -->
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]536<div class="doc_subsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]537 <a name="micro">The Low Level Issues</a>
538</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]539
540
541<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]542<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]543 <a name="ll_assert">Assert Liberally</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]544</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]545
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]546<div class="doc_text">
547
548<p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]549preconditions and assumptions, you never know when a bug (not neccesarily even
550yours) might be caught early by an assertion, which reduces debugging time
551dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
552included by the header files you are using, so it doesn't cost anything to use
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]553it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]554
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]555<p>To further assist with debugging, make sure to put some kind of error message
556in the assertion statement (which is printed if the assertion is tripped). This
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]557helps the poor debugging make sense of why an assertion is being made and
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]558enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]559
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]560<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]561<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]562inline Value *getOperand(unsigned i) {
563 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
564 return Operands[i];
565}
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]566</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]567</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]568
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]569<p>Here are some examples:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]570
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]571<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]572<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]573assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]574
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]575assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]576
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]577assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]578
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]579assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]580
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]581assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]582</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]583</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]584
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]585<p>You get the idea...</p>
586
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]587<p>Please be aware when adding assert statements that not all compilers are aware of
588the semantics of the assert. In some places, asserts are used to indicate a piece of
589code that should not be reached. These are typically of the form:</p>
590
591<div class="doc_code">
592<pre>
Dan Gohmanf0032762008-11-24 17:18:39 +0000[diff] [blame]593assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]594</pre>
595</div>
596
597<p>When used in a function that returns a value, they should be followed with a return
598statement and a comment indicating that this line is never reached. This will prevent
599a compiler which is unable to deduce that the assert statement never returns from
600generating a warning.</p>
601
602<div class="doc_code">
603<pre>
Dan Gohmanf0032762008-11-24 17:18:39 +0000[diff] [blame]604assert(0 &amp;&amp; "Some helpful error message");
Nick Lewyckyf4408e82008-05-31 23:54:55 +0000[diff] [blame]605// Not reached
606return 0;
607</pre>
608</div>
609
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]610</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]611
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]612<!-- _______________________________________________________________________ -->
613<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]614 <a name="ll_ns_std">Do not use '<tt>using namespace std</tt>'</a>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]615</div>
616
617<div class="doc_text">
618<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]619namespace with an "<tt>std::</tt>" prefix, rather than rely on
620"<tt>using namespace std;</tt>".</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]621
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]622<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
Misha Brukman2d33c542008-12-11 19:37:04 +0000[diff] [blame]623the namespace of any source file that <tt>#include</tt>s the header. This is
624clearly a bad thing.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]625
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]626<p>In implementation files (e.g. .cpp files), the rule is more of a stylistic
627rule, but is still important. Basically, using explicit namespace prefixes
628makes the code <b>clearer</b>, because it is immediately obvious what facilities
629are being used and where they are coming from, and <b>more portable</b>, because
630namespace clashes cannot occur between LLVM code and other namespaces. The
631portability rule is important because different standard library implementations
632expose different symbols (potentially ones they shouldn't), and future revisions
633to the C++ standard will add more symbols to the <tt>std</tt> namespace. As
634such, we never use '<tt>using namespace std;</tt>' in LLVM.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]635
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]636<p>The exception to the general rule (i.e. it's not an exception for
637the <tt>std</tt> namespace) is for implementation files. For example, all of
638the code in the LLVM project implements code that lives in the 'llvm' namespace.
639As such, it is ok, and actually clearer, for the .cpp files to have a '<tt>using
640namespace llvm</tt>' directive at their top, after the <tt>#include</tt>s. The
641general form of this rule is that any .cpp file that implements code in any
642namespace may use that namespace (and its parents'), but should not use any
643others.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]644
645</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]646
647<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]648<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]649 <a name="ll_virtual_anch">Provide a virtual method anchor for classes
650 in headers</a>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]651</div>
652
653<div class="doc_text">
654
655<p>If a class is defined in a header file and has a v-table (either it has
656virtual methods or it derives from classes with virtual methods), it must
657always have at least one out-of-line virtual method in the class. Without
Misha Brukman2d33c542008-12-11 19:37:04 +0000[diff] [blame]658this, the compiler will copy the vtable and RTTI into every <tt>.o</tt> file
659that <tt>#include</tt>s the header, bloating <tt>.o</tt> file sizes and
660increasing link times.</p>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]661
662</div>
663
664
665<!-- _______________________________________________________________________ -->
666<div class="doc_subsubsection">
667 <a name="ll_preincrement">Prefer Preincrement</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]668</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]669
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]670<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]671
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]672<p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
673postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
674preincrementation whenever possible.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]675
676<p>The semantics of postincrement include making a copy of the value being
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]677incremented, returning it, and then preincrementing the "work value". For
678primitive types, this isn't a big deal... but for iterators, it can be a huge
679issue (for example, some iterators contains stack and set objects in them...
680copying an iterator could invoke the copy ctor's of these as well). In general,
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]681get in the habit of always using preincrement, and you won't have a problem.</p>
682
683</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]684
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]685<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]686<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]687 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]688</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]689
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]690<div class="doc_text">
691
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]692<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
693to the output stream specified. In addition to doing this, however, it also
694flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]695
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]696<div class="doc_code">
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]697<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]698std::cout &lt;&lt; std::endl;
699std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]700</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]701</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]702
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]703<p>Most of the time, you probably have no reason to flush the output stream, so
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]704it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]705
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]706</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]707
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]708
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]709<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]710<div class="doc_section">
711 <a name="seealso">See Also</a>
712</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]713<!-- *********************************************************************** -->
714
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]715<div class="doc_text">
716
717<p>A lot of these comments and recommendations have been culled for other
718sources. Two particularly important books for our work are:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]719
720<ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]721
Chris Lattner788ee282007-11-09 21:49:08 +0000[diff] [blame]722<li><a href="http://www.amazon.com/Effective-Specific-Addison-Wesley-Professional-Computing/dp/0321334876">Effective
723C++</a> by Scott Meyers. Also
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]724interesting and useful are "More Effective C++" and "Effective STL" by the same
725author.</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]726
Chris Lattner788ee282007-11-09 21:49:08 +0000[diff] [blame]727<li>Large-Scale C++ Software Design by John Lakos</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]728
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]729</ol>
730
731<p>If you get some free time, and you haven't read them: do so, you might learn
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]732something.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]733
734</div>
735
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]736<!-- *********************************************************************** -->
737
738<hr>
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]739<address>
740 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]741 src="http://jigsaw.w3.org/css-validator/images/vcss-blue" alt="Valid CSS"></a>
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]742 <a href="http://validator.w3.org/check/referer"><img
Misha Brukman44408702008-12-11 17:34:48 +0000[diff] [blame]743 src="http://www.w3.org/Icons/valid-html401-blue" alt="Valid HTML 4.01"></a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]744
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]745 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]746 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]747 Last modified: $Date$
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]748</address>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]749
750</body>
751</html>