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4<head>
5 <link rel="stylesheet" href="llvm.css" type="text/css">
6 <title>A Few Coding Standards</title>
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">
11 A Few Coding Standards
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
125<p>Every source file should have a header on it that
126describes the basic purpose of the file. If a file does not have a header, it
127should not be checked into CVS. Most source trees will probably have a standard
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++ -*-===//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]134//
135// The LLVM Compiler Infrastructure
136//
137// This file was developed by the LLVM research group and is distributed under
138// the University of Illinois Open Source License. See LICENSE.TXT for details.
139//
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 Lattner999cf092004-05-23 21:05:07 +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 Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]157<p>The next section in the file is a concise note that defines the license that
158the file is released under. This makes it perfectly clear what terms the source
159code can be distributed under.</p>
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
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]241<p>... and each catagory 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
265</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]266
267<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]268<div class="doc_subsubsection">
269 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
270</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]271
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]272<div class="doc_text">
273
274<p>In all cases, prefer spaces to tabs in source files. People have different
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]275prefered indentation levels, and different styles of indentation that they
276like... this is fine. What isn't is that different editors/viewers expand tabs
277out to different tab stops. This can cause your code to look completely
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]278unreadable, and it is not worth dealing with.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]279
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]280<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]281style of existing code if your are modifying and extending it. If you like four
282spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
283with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]284makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]285
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]286</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]287
288<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]289<div class="doc_subsubsection">
290 <a name="scf_indentation">Indent Code Consistently</a>
291</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]292
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]293<div class="doc_text">
294
295<p>Okay, your first year of programming you were told that indentation is
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]296important. If you didn't believe and internalize this then, now is the time.
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]297Just do it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]298
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]299</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]300
301
302<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]303<div class="doc_subsection">
304 <a name="compilerissues">Compiler Issues</a>
305</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]306
307
308<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]309<div class="doc_subsubsection">
310 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
311</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]312
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]313<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]314
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]315<p>If your code has compiler warnings in it, something is wrong: you aren't
316casting values correctly, your have "questionable" constructs in your code, or
317you are doing something legitimately wrong. Compiler warnings can cover up
318legitimate errors in output and make dealing with a translation unit
319difficult.</p>
320
321<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]322desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
323a good thorough set of warnings, and stick to them. At least in the case of
324<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
325syntax of the code slightly. For example, an warning that annoys me occurs when
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]326I write code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]327
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]328<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]329<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]330if (V = getValue()) {
331 ...
332}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]333</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]334</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]335
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]336<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
337operator, and that I probably mistyped it. In most cases, I haven't, and I
338really don't want the spurious errors. To fix this particular problem, I
339rewrite the code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]340
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]341<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]342<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]343if ((V = getValue())) {
344 ...
345}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]346</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]347</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]348
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]349<p>...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
350be fixed by massaging the code appropriately.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]351
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]352<p>These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall
353-Winline -W -Wwrite-strings -Wno-unused</tt></p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]354
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]355</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]356
357<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]358<div class="doc_subsubsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]359 <a name="ci_portable_code">Write Portable Code</a>
360</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]361
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]362<div class="doc_text">
363
364<p>In almost all cases, it is possible and within reason to write completely
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]365portable code. If there are cases where it isn't possible to write portable
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]366code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]367
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]368<p>In practice, this means that you shouldn't assume much about the host
369compiler, including its support for "high tech" features like partial
370specialization of templates. In fact, Visual C++ 6 could be an important target
371for our work in the future, and we don't want to have to rewrite all of our code
372to support it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]373
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]374</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]375
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]376<!-- _______________________________________________________________________ -->
377<div class="doc_subsubsection">
378<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
379</div>
380<div class="doc_text">
Misha Brukmanedcc78a2004-10-26 15:45:13 +0000[diff] [blame]381
382<p>In C++, the <tt>class</tt> and <tt>struct</tt> keywords can be used almost
383interchangeably. The only difference is when they are used to declare a class:
384<tt>class</tt> makes all members private by default while <tt>struct</tt> makes
385all members public by default.</p>
386
387<p>Unfortunately, not all compilers follow the rules and some will generate
388different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used to
389declare the symbol. This can lead to problems at link time.</p>
390
391<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
392<b>all</b> members are public, in which case <tt>struct</tt> is allowed.</p>
393
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]394</div>
395
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]396<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]397<div class="doc_section">
398 <a name="styleissues">Style Issues</a>
399</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]400<!-- *********************************************************************** -->
401
402
403<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]404<div class="doc_subsection">
405 <a name="macro">The High Level Issues</a>
406</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]407
408
409<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]410<div class="doc_subsubsection">
411 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
412</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]413
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]414<div class="doc_text">
415
416<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]417encapsulation or data hiding (unless you use expensive protocol classes), but it
418is what we have to work with. When you write a public header file (in the LLVM
419source tree, they live in the top level "include" directory), you are defining a
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]420module of functionality.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]421
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]422<p>Ideally, modules should be completely independent of each other, and their
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]423header files should only include the absolute minimum number of headers
424possible. A module is not just a class, a function, or a namespace: <a
425href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection
426of these</a> that defines an interface. This interface may be several
427functions, classes or data structures, but the important issue is how they work
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]428together.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]429
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]430<p>In general, a module should be implemented with one or more <tt>.cpp</tt>
431files. Each of these <tt>.cpp</tt> files should include the header that defines
432their interface first. This ensure that all of the dependences of the module
433header have been properly added to the module header itself, and are not
434implicit. System headers should be included after user headers for a
435translation unit.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]436
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]437</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]438
439<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]440<div class="doc_subsubsection">
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]441 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]442</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]443
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]444<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]445
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]446<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
447have to, especially in header files.</p>
448
449<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]450to inherit from it. In these cases go ahead and <tt>#include</tt> that header
451file. Be aware however that there are many cases where you don't need to have
452the full definition of a class. If you are using a pointer or reference to a
453class, you don't need the header file. If you are simply returning a class
454instance from a prototyped function or method, you don't need it. In fact, for
455most cases, you simply don't need the definition of a class... and not
456<tt>#include</tt>'ing speeds up compilation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]457
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]458<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]459<b>must</b> include all of the header files that you are using -- you can
460include them either directly
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]461or indirectly (through another header file). To make sure that you don't
462accidently forget to include a header file in your module header, make sure to
463include your module header <b>first</b> in the implementation file (as mentioned
464above). This way there won't be any hidden dependencies that you'll find out
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]465about later...</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]466
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]467</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]468
469<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]470<div class="doc_subsubsection">
471 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
472</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]473
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]474<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]475
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]476<p>Many modules have a complex implementation that causes them to use more than
477one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
478internal communication interface (helper classes, extra functions, etc) in the
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]479public module header file. Don't do this.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]480
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]481<p>If you really need to do something like this, put a private header file in
482the same directory as the source files, and include it locally. This ensures
483that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]484
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]485<p>Note however, that it's okay to put extra implementation methods a public
486class itself... just make them private (or protected), and all is well.</p>
487
488</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]489
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]490<!-- _______________________________________________________________________ -->
491<div class="doc_subsubsection">
492 <a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is forbidden</a>
493</div>
494
495<div class="doc_text">
496
497<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
498hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
499support clients using LLVM libraries as part of larger systems. In particular,
500we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
501the static c'tors are run whenever an application start up that uses the dynamic
502library. There are two problems with this:</p>
503
504<ol>
505 <li>The time to run the static c'tors impacts startup time of
506 applications&mdash;a critical time for gui apps.</li>
507 <li>The static c'tors cause the app to pull many extra pages of memory off the
508 disk: both the code for the static c'tors in each .o file and the small
509 amount of data that gets touched. In addition, touched/dirty pages put
510 more pressure on the VM system on low-memory machines.</li>
511</ol>
512
Bill Wendlingb0a9d1b2006-12-17 11:40:40 +0000[diff] [blame]513<table align="center">
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]514 <tbody>
515 <tr>
516 <th>Old Way</th>
517 <th>New Way</th>
518 </tr>
519 <tr>
520 <td align="left"><pre>#include &lt;iostream&gt;</pre></td>
521 <td align="left"><pre>#include "llvm/Support/Streams.h"</pre></td>
522 </tr>
523 <tr>
Bill Wendlingb0a9d1b2006-12-17 11:40:40 +0000[diff] [blame]524 <td align="left"><pre>DEBUG(std::cerr &lt;&lt; ...);
525DEBUG(dump(std::cerr));</pre></td>
526 <td align="left"><pre>DOUT &lt;&lt; ...;
527dump(DOUT);</pre></td>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]528 </tr>
529 <tr>
530 <td align="left"><pre>std::cerr &lt;&lt; "Hello world\n";</pre></td>
531 <td align="left"><pre>llvm::cerr &lt;&lt; "Hello world\n";</pre></td>
532 </tr>
533 <tr>
534 <td align="left"><pre>std::cout &lt;&lt; "Hello world\n";</pre></td>
535 <td align="left"><pre>llvm::cout &lt;&lt; "Hello world\n";</pre></td>
536 </tr>
537 <tr>
538 <td align="left"><pre>std::cin &gt;&gt; Var;</pre></td>
539 <td align="left"><pre>llvm::cin &gt;&gt; Var;</pre></td>
540 </tr>
541 <tr>
542 <td align="left"><pre>std::ostream</pre></td>
543 <td align="left"><pre>llvm::OStream</pre></td>
544 </tr>
545 <tr>
546 <td align="left"><pre>std::istream</pre></td>
547 <td align="left"><pre>llvm::IStream</pre></td>
548 </tr>
549 <tr>
550 <td align="left"><pre>std::stringstream</pre></td>
551 <td align="left"><pre>llvm::StringStream</pre></td>
552 </tr>
Bill Wendling0f7c10d2006-12-09 01:27:51 +0000[diff] [blame]553 <tr>
554 <td align="left"><pre>void print(std::ostream &Out);
555// ...
556print(std::cerr);</pre></td>
557 <td align="left"><pre>void print(std::ostream &Out);
Bill Wendlingb0a9d1b2006-12-17 11:40:40 +0000[diff] [blame]558void print(std::ostream *Out) { if (Out) print(*Out) }
Bill Wendling0f7c10d2006-12-09 01:27:51 +0000[diff] [blame]559// ...
Bill Wendlingb0a9d1b2006-12-17 11:40:40 +0000[diff] [blame]560print(llvm::cerr);</pre>
561
562<ul><i>N.B.</i> The second <tt>print</tt> method is called by the <tt>print</tt>
563expression. It prevents the execution of the first <tt>print</tt> method if the
564stream is <tt>cnull</tt>.</ul></td>
565 </tbody>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]566</table>
567
568</div>
569
570
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]571<!-- ======================================================================= -->
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]572<div class="doc_subsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]573 <a name="micro">The Low Level Issues</a>
574</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]575
576
577<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]578<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]579 <a name="ll_assert">Assert Liberally</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]580</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]581
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]582<div class="doc_text">
583
584<p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]585preconditions and assumptions, you never know when a bug (not neccesarily even
586yours) might be caught early by an assertion, which reduces debugging time
587dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
588included 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]589it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]590
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]591<p>To further assist with debugging, make sure to put some kind of error message
592in the assertion statement (which is printed if the assertion is tripped). This
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]593helps the poor debugging make sense of why an assertion is being made and
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]594enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]595
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]596<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]597<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]598inline Value *getOperand(unsigned i) {
599 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
600 return Operands[i];
601}
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]602</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]603</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]604
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]605<p>Here are some examples:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]606
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]607<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]608<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]609assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]610
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]611assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]612
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]613assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]614
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]615assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]616
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]617assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]618</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]619</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]620
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]621<p>You get the idea...</p>
622
623</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]624
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]625<!-- _______________________________________________________________________ -->
626<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]627 <a name="ll_ns_std">Do not use '<tt>using namespace std</tt>'</a>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]628</div>
629
630<div class="doc_text">
631<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]632namespace with an "<tt>std::</tt>" prefix, rather than rely on
633"<tt>using namespace std;</tt>".</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]634
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]635<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
636the namespace of any source file that includes the header. This is clearly a
637bad thing.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]638
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]639<p>In implementation files (e.g. .cpp files), the rule is more of a stylistic
640rule, but is still important. Basically, using explicit namespace prefixes
641makes the code <b>clearer</b>, because it is immediately obvious what facilities
642are being used and where they are coming from, and <b>more portable</b>, because
643namespace clashes cannot occur between LLVM code and other namespaces. The
644portability rule is important because different standard library implementations
645expose different symbols (potentially ones they shouldn't), and future revisions
646to the C++ standard will add more symbols to the <tt>std</tt> namespace. As
647such, we never use '<tt>using namespace std;</tt>' in LLVM.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]648
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]649<p>The exception to the general rule (i.e. it's not an exception for
650the <tt>std</tt> namespace) is for implementation files. For example, all of
651the code in the LLVM project implements code that lives in the 'llvm' namespace.
652As such, it is ok, and actually clearer, for the .cpp files to have a '<tt>using
653namespace llvm</tt>' directive at their top, after the <tt>#include</tt>s. The
654general form of this rule is that any .cpp file that implements code in any
655namespace may use that namespace (and its parents'), but should not use any
656others.</p>
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]657
658</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]659
660<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]661<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]662 <a name="ll_virtual_anch">Provide a virtual method anchor for classes
663 in headers</a>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]664</div>
665
666<div class="doc_text">
667
668<p>If a class is defined in a header file and has a v-table (either it has
669virtual methods or it derives from classes with virtual methods), it must
670always have at least one out-of-line virtual method in the class. Without
671this, the compiler will copy the vtable and RTTI into every .o file that
672#includes the header, bloating .o file sizes and increasing link times.
673</p>
674
675</div>
676
677
678<!-- _______________________________________________________________________ -->
679<div class="doc_subsubsection">
680 <a name="ll_preincrement">Prefer Preincrement</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]681</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]682
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]683<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]684
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]685<p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
686postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
687preincrementation whenever possible.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]688
689<p>The semantics of postincrement include making a copy of the value being
Misha Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]690incremented, returning it, and then preincrementing the "work value". For
691primitive types, this isn't a big deal... but for iterators, it can be a huge
692issue (for example, some iterators contains stack and set objects in them...
693copying an iterator could invoke the copy ctor's of these as well). In general,
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]694get in the habit of always using preincrement, and you won't have a problem.</p>
695
696</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]697
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]698<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]699<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]700 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
Misha Brukman75f258e2003-10-24 17:57:33 +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<div class="doc_text">
704
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]705<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
706to the output stream specified. In addition to doing this, however, it also
707flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]708
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]709<div class="doc_code">
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]710<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]711std::cout &lt;&lt; std::endl;
712std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]713</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]714</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]715
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]716<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]717it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]718
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]719</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]720
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]721
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]722<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]723<div class="doc_section">
724 <a name="seealso">See Also</a>
725</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]726<!-- *********************************************************************** -->
727
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]728<div class="doc_text">
729
730<p>A lot of these comments and recommendations have been culled for other
731sources. Two particularly important books for our work are:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]732
733<ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]734
Tanya Lattner09cf73c2004-06-22 04:24:55 +0000[diff] [blame]735<li><a href="http://www.aw-bc.com/catalog/academic/product/0,1144,0201310155,00.html">Effective
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]736C++</a> by Scott Meyers. There is an online version of the book (only some
737chapters though) <a
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]738href="http://www.awlonline.com/cseng/meyerscddemo/">available as well</a>. Also
739interesting and useful are "More Effective C++" and "Effective STL" by the same
740author.</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]741
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]742<li><a href="http://cseng.aw.com/book/0,3828,0201633620,00.html">Large-Scale C++
743Software Design</a> by John Lakos</li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]744
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]745</ol>
746
747<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]748something.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]749
750</div>
751
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]752<!-- *********************************************************************** -->
753
754<hr>
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]755<address>
756 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
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Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]760
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]761 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]762 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]763 Last modified: $Date$
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]764</address>
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