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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
Reid Spencerc7f87f22007-07-09 08:04:31 +0000[diff] [blame^]125<p>Every source file should have a header on it that describes the basic
126purpose of the file. If a file does not have a header, it should not be
127checked into Subversion. Most source trees will probably have a standard
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]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//
Chris Lattner85030072007-02-19 03:33:06 +0000[diff] [blame]137// This file was developed by &lt;whoever started the file&gt; and is distributed under
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]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 Lattner85030072007-02-19 03:33:06 +0000[diff] [blame]149<p>A few things to note about this particular format: The 'developed by' line
150should be the name of the person or organization who initially contributed the
151file. The "<tt>-*- C++
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]152-*-</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]153is a C++ file, not a C file (Emacs assumes .h files are C files by default).
154Note that this tag is not necessary in .cpp files. The name of the file is also
155on the first line, along with a very short description of the purpose of the
156file. This is important when printing out code and flipping though lots of
157pages.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]158
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]159<p>The next section in the file is a concise note that defines the license that
160the file is released under. This makes it perfectly clear what terms the source
161code can be distributed under.</p>
162
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]163<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]164Here it's only two lines. If an algorithm is being implemented or something
165tricky is going on, a reference to the paper where it is published should be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]166included, 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]167
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]168<b>Class overviews</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]169
Jim Laskey88b5e792006-07-31 20:18:49 +0000[diff] [blame]170<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]171a class definition should have a comment block that explains what the class is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]172used for... if it's not obvious. If it's so completely obvious your grandma
173could figure it out, it's probably safe to leave it out. Naming classes
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]174something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]175
176
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]177<b>Method information</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]178
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]179<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]180documented properly. A quick note about what it does any a description of the
181borderline behaviour is all that is necessary here (unless something
182particularly tricky or insideous is going on). The hope is that people can
183figure out how to use your interfaces without reading the code itself... that is
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]184the goal metric.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]185
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]186<p>Good things to talk about here are what happens when something unexpected
187happens: does the method return null? Abort? Format your hard disk?</p>
188
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]189</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]190
191<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]192<div class="doc_subsubsection">
193 <a name="scf_commentformat">Comment Formatting</a>
194</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]195
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]196<div class="doc_text">
197
198<p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]199require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]200when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]201
202<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]203 <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]204 comments.</li>
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]205 <li>When writing a header file that may be <tt>#include</tt>d by a C source
206 file.</li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]207 <li>When writing a source file that is used by a tool that only accepts C
208 style comments.</li>
209</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]210
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]211<p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
212These nest properly and are better behaved in general than C style comments.</p>
213
214</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]215
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]216<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]217<div class="doc_subsubsection">
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]218 <a name="scf_includes"><tt>#include</tt> Style</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]219</div>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]220
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]221<div class="doc_text">
222
223<p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]224include guards if working on a header file), the <a
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]225href="#hl_dontinclude">minimal</a> list of <tt>#include</tt>s required by the
226file should be listed. We prefer these <tt>#include</tt>s to be listed in this
227order:</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]228
229<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]230 <li><a href="#mmheader">Main Module header</a></li>
231 <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]232 <li><tt>llvm/*</tt></li>
233 <li><tt>llvm/Analysis/*</tt></li>
234 <li><tt>llvm/Assembly/*</tt></li>
235 <li><tt>llvm/Bytecode/*</tt></li>
236 <li><tt>llvm/CodeGen/*</tt></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]237 <li>...</li>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]238 <li><tt>Support/*</tt></li>
239 <li><tt>Config/*</tt></li>
240 <li>System <tt>#includes</tt></li>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]241</ol>
242
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]243<p>... and each catagory should be sorted by name.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]244
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]245<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]246which implement an interface defined by a .h file. This <tt>#include</tt>
247should always be included <b>first</b> regardless of where it lives on the file
248system. By including a header file first in the .cpp files that implement the
249interfaces, we ensure that the header does not have any hidden dependencies
250which are not explicitly #included in the header, but should be. It is also a
251form of documentation in the .cpp file to indicate where the interfaces it
252implements are defined.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]253
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]254</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]255
256<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]257<div class="doc_subsubsection">
258 <a name="scf_codewidth">Source Code Width</a>
259</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]260
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]261<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]262
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]263<p>Write your code to fit within 80 columns of text. This helps those of us who
264like to print out code and look at your code in an xterm without resizing
265it.</p>
266
267</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]268
269<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]270<div class="doc_subsubsection">
271 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
272</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]273
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]274<div class="doc_text">
275
276<p>In all cases, prefer spaces to tabs in source files. People have different
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]277prefered indentation levels, and different styles of indentation that they
278like... this is fine. What isn't is that different editors/viewers expand tabs
279out to different tab stops. This can cause your code to look completely
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]280unreadable, and it is not worth dealing with.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]281
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]282<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]283style of existing code if your are modifying and extending it. If you like four
284spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
285with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]286makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]287
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]288</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]289
290<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]291<div class="doc_subsubsection">
292 <a name="scf_indentation">Indent Code Consistently</a>
293</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]294
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]295<div class="doc_text">
296
297<p>Okay, your first year of programming you were told that indentation is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]298important. If you didn't believe and internalize this then, now is the time.
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]299Just do it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]300
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]301</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]302
303
304<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]305<div class="doc_subsection">
306 <a name="compilerissues">Compiler Issues</a>
307</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]308
309
310<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]311<div class="doc_subsubsection">
312 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
313</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]314
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]315<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]316
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]317<p>If your code has compiler warnings in it, something is wrong: you aren't
318casting values correctly, your have "questionable" constructs in your code, or
319you are doing something legitimately wrong. Compiler warnings can cover up
320legitimate errors in output and make dealing with a translation unit
321difficult.</p>
322
323<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]324desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
325a good thorough set of warnings, and stick to them. At least in the case of
326<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
327syntax of the code slightly. For example, an warning that annoys me occurs when
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]328I write code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]329
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]330<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]331<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]332if (V = getValue()) {
333 ...
334}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]335</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]336</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]337
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]338<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
339operator, and that I probably mistyped it. In most cases, I haven't, and I
340really don't want the spurious errors. To fix this particular problem, I
341rewrite the code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]342
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]343<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]344<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]345if ((V = getValue())) {
346 ...
347}
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]348</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]349</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]350
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]351<p>...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
352be fixed by massaging the code appropriately.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]353
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]354<p>These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall
355-Winline -W -Wwrite-strings -Wno-unused</tt></p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]356
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]357</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]358
359<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]360<div class="doc_subsubsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]361 <a name="ci_portable_code">Write Portable Code</a>
362</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]363
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]364<div class="doc_text">
365
366<p>In almost all cases, it is possible and within reason to write completely
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]367portable code. If there are cases where it isn't possible to write portable
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]368code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]369
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]370<p>In practice, this means that you shouldn't assume much about the host
371compiler, including its support for "high tech" features like partial
372specialization of templates. In fact, Visual C++ 6 could be an important target
373for our work in the future, and we don't want to have to rewrite all of our code
374to support it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]375
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]376</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]377
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]378<!-- _______________________________________________________________________ -->
379<div class="doc_subsubsection">
380<a name="ci_class_struct">Use of <tt>class</tt> and <tt>struct</tt> Keywords</a>
381</div>
382<div class="doc_text">
Misha Brukmanf2499132004-10-26 15:45:13 +0000[diff] [blame]383
384<p>In C++, the <tt>class</tt> and <tt>struct</tt> keywords can be used almost
385interchangeably. The only difference is when they are used to declare a class:
386<tt>class</tt> makes all members private by default while <tt>struct</tt> makes
387all members public by default.</p>
388
389<p>Unfortunately, not all compilers follow the rules and some will generate
390different symbols based on whether <tt>class</tt> or <tt>struct</tt> was used to
391declare the symbol. This can lead to problems at link time.</p>
392
393<p>So, the rule for LLVM is to always use the <tt>class</tt> keyword, unless
394<b>all</b> members are public, in which case <tt>struct</tt> is allowed.</p>
395
Reid Spencerbf6439f2004-09-23 16:03:48 +0000[diff] [blame]396</div>
397
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]398<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]399<div class="doc_section">
400 <a name="styleissues">Style Issues</a>
401</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]402<!-- *********************************************************************** -->
403
404
405<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]406<div class="doc_subsection">
407 <a name="macro">The High Level Issues</a>
408</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]409
410
411<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]412<div class="doc_subsubsection">
413 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
414</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]415
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]416<div class="doc_text">
417
418<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]419encapsulation or data hiding (unless you use expensive protocol classes), but it
420is what we have to work with. When you write a public header file (in the LLVM
421source tree, they live in the top level "include" directory), you are defining a
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]422module of functionality.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]423
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]424<p>Ideally, modules should be completely independent of each other, and their
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]425header files should only include the absolute minimum number of headers
426possible. A module is not just a class, a function, or a namespace: <a
427href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection
428of these</a> that defines an interface. This interface may be several
429functions, classes or data structures, but the important issue is how they work
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]430together.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]431
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]432<p>In general, a module should be implemented with one or more <tt>.cpp</tt>
433files. Each of these <tt>.cpp</tt> files should include the header that defines
434their interface first. This ensure that all of the dependences of the module
435header have been properly added to the module header itself, and are not
436implicit. System headers should be included after user headers for a
437translation unit.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]438
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]439</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]440
441<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]442<div class="doc_subsubsection">
Misha Brukman03f87d52004-10-26 16:18:43 +0000[diff] [blame]443 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]444</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]445
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]446<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]447
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]448<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
449have to, especially in header files.</p>
450
451<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]452to inherit from it. In these cases go ahead and <tt>#include</tt> that header
453file. Be aware however that there are many cases where you don't need to have
454the full definition of a class. If you are using a pointer or reference to a
455class, you don't need the header file. If you are simply returning a class
456instance from a prototyped function or method, you don't need it. In fact, for
457most cases, you simply don't need the definition of a class... and not
458<tt>#include</tt>'ing speeds up compilation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]459
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]460<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]461<b>must</b> include all of the header files that you are using -- you can
462include them either directly
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]463or indirectly (through another header file). To make sure that you don't
464accidently forget to include a header file in your module header, make sure to
465include your module header <b>first</b> in the implementation file (as mentioned
466above). This way there won't be any hidden dependencies that you'll find out
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]467about later...</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]468
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]469</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]470
471<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]472<div class="doc_subsubsection">
473 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
474</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]475
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]476<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]477
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]478<p>Many modules have a complex implementation that causes them to use more than
479one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
480internal communication interface (helper classes, extra functions, etc) in the
Misha Brukman6d1686c2004-12-04 00:32:12 +0000[diff] [blame]481public module header file. Don't do this.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]482
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]483<p>If you really need to do something like this, put a private header file in
484the same directory as the source files, and include it locally. This ensures
485that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]486
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]487<p>Note however, that it's okay to put extra implementation methods a public
488class itself... just make them private (or protected), and all is well.</p>
489
490</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]491
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]492<!-- _______________________________________________________________________ -->
493<div class="doc_subsubsection">
494 <a name="ll_iostream"><tt>#include &lt;iostream&gt;</tt> is forbidden</a>
495</div>
496
497<div class="doc_text">
498
499<p>The use of <tt>#include &lt;iostream&gt;</tt> in library files is
500hereby <b><em>forbidden</em></b>. The primary reason for doing this is to
501support clients using LLVM libraries as part of larger systems. In particular,
502we statically link LLVM into some dynamic libraries. Even if LLVM isn't used,
503the static c'tors are run whenever an application start up that uses the dynamic
504library. There are two problems with this:</p>
505
506<ol>
507 <li>The time to run the static c'tors impacts startup time of
508 applications&mdash;a critical time for gui apps.</li>
509 <li>The static c'tors cause the app to pull many extra pages of memory off the
510 disk: both the code for the static c'tors in each .o file and the small
511 amount of data that gets touched. In addition, touched/dirty pages put
512 more pressure on the VM system on low-memory machines.</li>
513</ol>
514
Bill Wendling33072442006-12-17 11:40:40 +0000[diff] [blame]515<table align="center">
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]516 <tbody>
517 <tr>
518 <th>Old Way</th>
519 <th>New Way</th>
520 </tr>
521 <tr>
522 <td align="left"><pre>#include &lt;iostream&gt;</pre></td>
523 <td align="left"><pre>#include "llvm/Support/Streams.h"</pre></td>
524 </tr>
525 <tr>
Bill Wendling33072442006-12-17 11:40:40 +0000[diff] [blame]526 <td align="left"><pre>DEBUG(std::cerr &lt;&lt; ...);
527DEBUG(dump(std::cerr));</pre></td>
528 <td align="left"><pre>DOUT &lt;&lt; ...;
529dump(DOUT);</pre></td>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]530 </tr>
531 <tr>
532 <td align="left"><pre>std::cerr &lt;&lt; "Hello world\n";</pre></td>
533 <td align="left"><pre>llvm::cerr &lt;&lt; "Hello world\n";</pre></td>
534 </tr>
535 <tr>
536 <td align="left"><pre>std::cout &lt;&lt; "Hello world\n";</pre></td>
537 <td align="left"><pre>llvm::cout &lt;&lt; "Hello world\n";</pre></td>
538 </tr>
539 <tr>
540 <td align="left"><pre>std::cin &gt;&gt; Var;</pre></td>
541 <td align="left"><pre>llvm::cin &gt;&gt; Var;</pre></td>
542 </tr>
543 <tr>
544 <td align="left"><pre>std::ostream</pre></td>
545 <td align="left"><pre>llvm::OStream</pre></td>
546 </tr>
547 <tr>
548 <td align="left"><pre>std::istream</pre></td>
549 <td align="left"><pre>llvm::IStream</pre></td>
550 </tr>
551 <tr>
552 <td align="left"><pre>std::stringstream</pre></td>
553 <td align="left"><pre>llvm::StringStream</pre></td>
554 </tr>
Bill Wendlingc78ae262006-12-09 01:27:51 +0000[diff] [blame]555 <tr>
556 <td align="left"><pre>void print(std::ostream &Out);
557// ...
558print(std::cerr);</pre></td>
559 <td align="left"><pre>void print(std::ostream &Out);
Bill Wendling33072442006-12-17 11:40:40 +0000[diff] [blame]560void print(std::ostream *Out) { if (Out) print(*Out) }
Bill Wendlingc78ae262006-12-09 01:27:51 +0000[diff] [blame]561// ...
Bill Wendling33072442006-12-17 11:40:40 +0000[diff] [blame]562print(llvm::cerr);</pre>
563
564<ul><i>N.B.</i> The second <tt>print</tt> method is called by the <tt>print</tt>
565expression. It prevents the execution of the first <tt>print</tt> method if the
566stream is <tt>cnull</tt>.</ul></td>
567 </tbody>
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]568</table>
569
570</div>
571
572
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]573<!-- ======================================================================= -->
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]574<div class="doc_subsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]575 <a name="micro">The Low Level Issues</a>
576</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]577
578
579<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]580<div class="doc_subsubsection">
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]581 <a name="ll_assert">Assert Liberally</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]582</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]583
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]584<div class="doc_text">
585
586<p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]587preconditions and assumptions, you never know when a bug (not neccesarily even
588yours) might be caught early by an assertion, which reduces debugging time
589dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
590included 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]591it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]592
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]593<p>To further assist with debugging, make sure to put some kind of error message
594in the assertion statement (which is printed if the assertion is tripped). This
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]595helps the poor debugging make sense of why an assertion is being made and
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]596enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]597
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]598<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]599<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]600inline Value *getOperand(unsigned i) {
601 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
602 return Operands[i];
603}
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]604</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]605</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]606
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]607<p>Here are some examples:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]608
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]609<div class="doc_code">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]610<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]611assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]612
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]613assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]614
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]615assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]616
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]617assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]618
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]619assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]620</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]621</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]622
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]623<p>You get the idea...</p>
624
625</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]626
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]627<!-- _______________________________________________________________________ -->
628<div class="doc_subsubsection">
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]629 <a name="ll_ns_std">Do not use '<tt>using namespace std</tt>'</a>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]630</div>
631
632<div class="doc_text">
633<p>In LLVM, we prefer to explicitly prefix all identifiers from the standard
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]634namespace with an "<tt>std::</tt>" prefix, rather than rely on
635"<tt>using namespace std;</tt>".</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]636
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]637<p> In header files, adding a '<tt>using namespace XXX</tt>' directive pollutes
638the namespace of any source file that includes the header. This is clearly a
639bad thing.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]640
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]641<p>In implementation files (e.g. .cpp files), the rule is more of a stylistic
642rule, but is still important. Basically, using explicit namespace prefixes
643makes the code <b>clearer</b>, because it is immediately obvious what facilities
644are being used and where they are coming from, and <b>more portable</b>, because
645namespace clashes cannot occur between LLVM code and other namespaces. The
646portability rule is important because different standard library implementations
647expose different symbols (potentially ones they shouldn't), and future revisions
648to the C++ standard will add more symbols to the <tt>std</tt> namespace. As
649such, we never use '<tt>using namespace std;</tt>' in LLVM.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]650
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]651<p>The exception to the general rule (i.e. it's not an exception for
652the <tt>std</tt> namespace) is for implementation files. For example, all of
653the code in the LLVM project implements code that lives in the 'llvm' namespace.
654As such, it is ok, and actually clearer, for the .cpp files to have a '<tt>using
655namespace llvm</tt>' directive at their top, after the <tt>#include</tt>s. The
656general form of this rule is that any .cpp file that implements code in any
657namespace may use that namespace (and its parents'), but should not use any
658others.</p>
Chris Lattner01e81e62006-01-01 21:59:22 +0000[diff] [blame]659
660</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]661
662<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]663<div class="doc_subsubsection">
Bill Wendlingb0629482006-12-09 01:35:43 +0000[diff] [blame]664 <a name="ll_virtual_anch">Provide a virtual method anchor for classes
665 in headers</a>
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]666</div>
667
668<div class="doc_text">
669
670<p>If a class is defined in a header file and has a v-table (either it has
671virtual methods or it derives from classes with virtual methods), it must
672always have at least one out-of-line virtual method in the class. Without
673this, the compiler will copy the vtable and RTTI into every .o file that
674#includes the header, bloating .o file sizes and increasing link times.
675</p>
676
677</div>
678
679
680<!-- _______________________________________________________________________ -->
681<div class="doc_subsubsection">
682 <a name="ll_preincrement">Prefer Preincrement</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]683</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]684
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]685<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]686
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]687<p>Hard fast rule: Preincrement (<tt>++X</tt>) may be no slower than
688postincrement (<tt>X++</tt>) and could very well be a lot faster than it. Use
689preincrementation whenever possible.</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]690
691<p>The semantics of postincrement include making a copy of the value being
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]692incremented, returning it, and then preincrementing the "work value". For
693primitive types, this isn't a big deal... but for iterators, it can be a huge
694issue (for example, some iterators contains stack and set objects in them...
695copying an iterator could invoke the copy ctor's of these as well). In general,
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]696get in the habit of always using preincrement, and you won't have a problem.</p>
697
698</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]699
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]700<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]701<div class="doc_subsubsection">
Chris Lattner85ea83e2006-07-27 04:24:14 +0000[diff] [blame]702 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]703</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]704
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]705<div class="doc_text">
706
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]707<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
708to the output stream specified. In addition to doing this, however, it also
709flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]710
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]711<div class="doc_code">
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]712<pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]713std::cout &lt;&lt; std::endl;
714std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]715</pre>
Misha Brukmanb2246152004-07-28 22:31:54 +0000[diff] [blame]716</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]717
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]718<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]719it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]720
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]721</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]722
Bill Wendling2b52dc12006-12-09 01:20:34 +0000[diff] [blame]723
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]724<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]725<div class="doc_section">
726 <a name="seealso">See Also</a>
727</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]728<!-- *********************************************************************** -->
729
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]730<div class="doc_text">
731
732<p>A lot of these comments and recommendations have been culled for other
733sources. Two particularly important books for our work are:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]734
735<ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]736
Tanya Lattner8ed32be2004-06-22 04:24:55 +0000[diff] [blame]737<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]738C++</a> by Scott Meyers. There is an online version of the book (only some
739chapters though) <a
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]740href="http://www.awlonline.com/cseng/meyerscddemo/">available as well</a>. Also
741interesting and useful are "More Effective C++" and "Effective STL" by the same
742author.</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]743
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]744<li><a href="http://cseng.aw.com/book/0,3828,0201633620,00.html">Large-Scale C++
745Software Design</a> by John Lakos</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]746
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]747</ol>
748
749<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]750something.</p>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]751
752</div>
753
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]754<!-- *********************************************************************** -->
755
756<hr>
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]757<address>
758 <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]762
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]763 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencerca058542006-03-14 05:39:39 +0000[diff] [blame]764 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]765 Last modified: $Date$
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]766</address>
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