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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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]9
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]10<div class="doc_title">
11 A Few Coding Standards
12</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]13
14<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner85014f42001-07-23 20:40:41 +0000[diff] [blame]16 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]17 <ol>
18 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukmanf196dbb2003-10-24 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 Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]22 <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]27 <li><a href="#compilerissues">Compiler Issues</a>
28 <ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]29 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
30 Errors</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]31 <li><a href="#ci_portable_code">Write Portable Code</a></li>
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]32 <li><a href="#ci_class_struct">Use of class/struct Keywords</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]33 </ol></li>
34 </ol></li>
Chris Lattnerac457c42001-07-09 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 Brukmanf196dbb2003-10-24 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 Wendling2b52dc12006-12-09 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]46 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]47 <li><a href="#micro">The Low Level Issues</a>
48 <ol>
Chris Lattner85ea83e2006-07-27 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 Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]51 <li><a href="#ll_virtual_anch">Provide a virtual method anchor for
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]52 classes in headers</a></li>
Chris Lattner85ea83e2006-07-27 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]55 </ol></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]56 </ol></li>
57 <li><a href="#seealso">See Also</a></li>
58</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]59
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]60<div class="doc_author">
Bill Wendling2b52dc12006-12-09 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 Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]63</div>
64
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]65
66<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]67<div class="doc_section">
68 <a name="introduction">Introduction</a>
69</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]70<!-- *********************************************************************** -->
71
Misha Brukmanf196dbb2003-10-24 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 Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]76absolute requirements to be followed in all instances, coding standards can be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]77useful.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]78
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]79<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]80issues such as brace placement and space usage. For issues like this, follow
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]81the golden rule:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]82
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]83<blockquote>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]84
Misha Brukmanf196dbb2003-10-24 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 Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]94maintainability of our common source base. If you have suggestions for topics to
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]95be included, please mail them to <a
96href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]97
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]98</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]99
100<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]101<div class="doc_section">
102 <a name="mechanicalissues">Mechanical Source Issues</a>
103</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]104<!-- *********************************************************************** -->
105
106<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]107<div class="doc_subsection">
108 <a name="sourceformating">Source Code Formatting</a>
109</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]110
111<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]112<div class="doc_subsubsection">
113 <a name="scf_commenting">Commenting</a>
114</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]115
Misha Brukmanf196dbb2003-10-24 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 Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]119knows they should comment, so should you. Although we all should probably
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]120comment our code more than we do, there are a few very critical places that
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]121documentation is very useful:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]122
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]123<b>File Headers</b>
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]130
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]131<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]132<pre>
Chris Lattnere6f4e072003-10-13 14:58:11 +0000[diff] [blame]133//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Chris Lattner1dab1922004-05-23 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 Lattnerac457c42001-07-09 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 Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]147</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]148
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]149<p>A few things to note about this particular format: The "<tt>-*- C++
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]150-*-</tt>" string on the first line is there to tell Emacs that the source file
Misha Brukman0d640e82004-07-28 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]156
Chris Lattner1dab1922004-05-23 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 Brukmanf196dbb2003-10-24 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 Brukman0cedb1f2003-10-06 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]164included, as well as any notes or "gotchas" in the code to watch out for.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]165
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]166<b>Class overviews</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]167
Jim Laskey88b5e792006-07-31 20:18:49 +0000[diff] [blame]168<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]169a class definition should have a comment block that explains what the class is
Misha Brukman0cedb1f2003-10-06 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 Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]172something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]173
174
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]175<b>Method information</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]176
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]177<p>Methods defined in a class (as well as any global functions) should also be
Misha Brukman0cedb1f2003-10-06 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]182the goal metric.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]183
Misha Brukmanf196dbb2003-10-24 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]187</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]188
189<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]190<div class="doc_subsubsection">
191 <a name="scf_commentformat">Comment Formatting</a>
192</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]193
Misha Brukmanf196dbb2003-10-24 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 Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]197require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]198when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]199
200<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]201 <li>When writing a C code: Obviously if you are writing C code, use C style
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]202 comments.</li>
Misha Brukman03f87d52004-10-26 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 Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]208
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]213
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]214<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]215<div class="doc_subsubsection">
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]216 <a name="scf_includes"><tt>#include</tt> Style</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]217</div>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]218
Misha Brukmanf196dbb2003-10-24 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 Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]222include guards if working on a header file), the <a
Misha Brukmanb2246152004-07-28 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 Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]226
227<ol>
Misha Brukmanf196dbb2003-10-24 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 Brukmanb2246152004-07-28 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]235 <li>...</li>
Misha Brukmanb2246152004-07-28 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 Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]239</ol>
240
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]241<p>... and each catagory should be sorted by name.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]242
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]243<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
Misha Brukman03f87d52004-10-26 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 Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]251
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]252</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]253
254<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]255<div class="doc_subsubsection">
256 <a name="scf_codewidth">Source Code Width</a>
257</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]258
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]259<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]260
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]266
267<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]271
Misha Brukmanf196dbb2003-10-24 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 Brukman0cedb1f2003-10-06 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]278unreadable, and it is not worth dealing with.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]279
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]280<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman0cedb1f2003-10-06 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]284makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]285
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]286</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]287
288<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]289<div class="doc_subsubsection">
290 <a name="scf_indentation">Indent Code Consistently</a>
291</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]292
Misha Brukmanf196dbb2003-10-24 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 Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]296important. If you didn't believe and internalize this then, now is the time.
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]297Just do it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]298
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]299</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]300
301
302<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]303<div class="doc_subsection">
304 <a name="compilerissues">Compiler Issues</a>
305</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]306
307
308<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]312
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]313<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]314
Misha Brukmanf196dbb2003-10-24 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 Brukman0cedb1f2003-10-06 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]326I write code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]327
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]328<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]329<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]330if (V = getValue()) {
331 ...
332}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]333</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]334</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]335
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]340
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]341<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]342<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]343if ((V = getValue())) {
344 ...
345}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]346</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]347</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]348
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]351
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]354
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]355</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]356
357<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]358<div class="doc_subsubsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]359 <a name="ci_portable_code">Write Portable Code</a>
360</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]361
Misha Brukmanf196dbb2003-10-24 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 Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]365portable code. If there are cases where it isn't possible to write portable
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]366code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]367
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]373
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]374</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]375
Reid Spencerbf6439f2004-09-23 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 Brukmanf2499132004-10-26 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 Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]394</div>
395
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]396<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]397<div class="doc_section">
398 <a name="styleissues">Style Issues</a>
399</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]400<!-- *********************************************************************** -->
401
402
403<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]404<div class="doc_subsection">
405 <a name="macro">The High Level Issues</a>
406</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]407
408
409<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]413
Misha Brukmanf196dbb2003-10-24 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 Brukmanc3e78932003-07-28 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]420module of functionality.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]421
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]422<p>Ideally, modules should be completely independent of each other, and their
Misha Brukmanc3e78932003-07-28 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]428together.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]429
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]436
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]437</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]438
439<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]440<div class="doc_subsubsection">
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]441 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]442</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]443
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]444<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]445
Misha Brukmanf196dbb2003-10-24 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 Brukman03f87d52004-10-26 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]457
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]458<p>It is easy to try to go too overboard on this recommendation, however. You
Chris Lattner756f83f2007-02-10 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 Brukmanc3e78932003-07-28 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]465about later...</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]466
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]467</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]468
469<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]470<div class="doc_subsubsection">
471 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
472</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]473
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]474<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]475
Misha Brukmanf196dbb2003-10-24 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 Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]479public module header file. Don't do this.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]480
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]484
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]489
Bill Wendling2b52dc12006-12-09 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 Wendling33072442006-12-17 11:40:40 +0000[diff] [blame]513<table align="center">
Bill Wendling2b52dc12006-12-09 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 Wendling33072442006-12-17 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 Wendling2b52dc12006-12-09 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 Wendlingc78ae262006-12-09 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 Wendling33072442006-12-17 11:40:40 +0000[diff] [blame]558void print(std::ostream *Out) { if (Out) print(*Out) }
Bill Wendlingc78ae262006-12-09 01:27:51 +0000[diff] [blame]559// ...
Bill Wendling33072442006-12-17 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 Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]566</table>
567
568</div>
569
570
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]571<!-- ======================================================================= -->
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]572<div class="doc_subsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]573 <a name="micro">The Low Level Issues</a>
574</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]575
576
577<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]578<div class="doc_subsubsection">
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]579 <a name="ll_assert">Assert Liberally</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]580</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]581
Misha Brukmanf196dbb2003-10-24 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 Brukmanc3e78932003-07-28 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]589it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]590
Misha Brukmanf196dbb2003-10-24 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 Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]593helps the poor debugging make sense of why an assertion is being made and
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]594enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]595
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]596<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]597<pre>
Misha Brukmanb2246152004-07-28 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]602</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]603</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]604
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]605<p>Here are some examples:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]606
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]607<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]608<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]609assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]610
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]611assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]612
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]613assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]614
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]615assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]616
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]617assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]618</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]619</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]620
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]621<p>You get the idea...</p>
622
623</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]624
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]625<!-- _______________________________________________________________________ -->
626<div class="doc_subsubsection">
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]627 <a name="ll_ns_std">Do not use '<tt>using namespace std</tt>'</a>
Chris Lattner01e81e62006-01-01 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 Wendlingb0629482006-12-09 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 Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]634
Bill Wendlingb0629482006-12-09 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 Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]638
Bill Wendlingb0629482006-12-09 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 Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]648
Bill Wendlingb0629482006-12-09 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 Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]657
658</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]659
660<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]661<div class="doc_subsubsection">
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]662 <a name="ll_virtual_anch">Provide a virtual method anchor for classes
663 in headers</a>
Chris Lattner85ea83e2006-07-27 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]681</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]682
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]683<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]684
Misha Brukmanb2246152004-07-28 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]688
689<p>The semantics of postincrement include making a copy of the value being
Misha Brukmanc3e78932003-07-28 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 Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]697
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]698<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]699<div class="doc_subsubsection">
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]700 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]701</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]702
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]703<div class="doc_text">
704
Chris Lattner1dab1922004-05-23 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 Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]708
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]709<div class="doc_code">
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]710<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]711std::cout &lt;&lt; std::endl;
712std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]713</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]714</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]715
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]716<p>Most of the time, you probably have no reason to flush the output stream, so
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]717it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]718
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]719</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]720
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]721
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]722<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]723<div class="doc_section">
724 <a name="seealso">See Also</a>
725</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]726<!-- *********************************************************************** -->
727
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]732
733<ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]734
Tanya Lattner8ed32be2004-06-22 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 Brukmanf196dbb2003-10-24 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 Lattner1dab1922004-05-23 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]741
Misha Brukmanf196dbb2003-10-24 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 Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]744
Misha Brukmanf196dbb2003-10-24 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 Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]748something.</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]749
750</div>
751
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]752<!-- *********************************************************************** -->
753
754<hr>
Misha Brukmand4f290a2004-05-12 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 Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]760
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]761 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]762 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]763 Last modified: $Date$
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]764</address>
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