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6 <title>A Few Coding Standards</title>
7</head>
8<body>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]9
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]10<div class="doc_title">
11 A Few Coding Standards
12</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]13
14<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner7ae36bb2001-07-23 20:40:41 +0000[diff] [blame]16 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]17 <ol>
18 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]19 <ol>
20 <li><a href="#scf_commenting">Commenting</a></li>
21 <li><a href="#scf_commentformat">Comment Formatting</a></li>
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]22 <li><a href="#scf_includes"><tt>#include</tt> Style</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]23 <li><a href="#scf_codewidth">Source Code Width</a></li>
24 <li><a href="#scf_spacestabs">Use Spaces Instead of Tabs</a></li>
25 <li><a href="#scf_indentation">Indent Code Consistently</a></li>
26 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]27 <li><a href="#compilerissues">Compiler Issues</a>
28 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]29 <li><a href="#ci_warningerrors">Treat Compiler Warnings Like
30 Errors</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]31 <li><a href="#ci_portable_code">Write Portable Code</a></li>
Reid Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]32 <li><a href="#ci_class_struct">Use of class/struct Keywords</a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]33 </ol></li>
34 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]35 <li><a href="#styleissues">Style Issues</a>
36 <ol>
37 <li><a href="#macro">The High Level Issues</a>
38 <ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]39 <li><a href="#hl_module">A Public Header File <b>is</b> a
40 Module</a></li>
41 <li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
42 <li><a href="#hl_privateheaders">Keep "internal" Headers
43 Private</a></li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]44 <li><a href="#ll_iostream"><tt>#include &lt;iostream&gt;</tt> is
45 <em>forbidden</em></a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]46 </ol></li>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]47 <li><a href="#micro">The Low Level Issues</a>
48 <ol>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]49 <li><a href="#ll_assert">Assert Liberally</a></li>
50 <li><a href="#ll_ns_std">Do not use 'using namespace std'</a></li>
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]51 <li><a href="#ll_virtual_anch">Provide a virtual method anchor for
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]52 classes in headers</a></li>
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]53 <li><a href="#ll_preincrement">Prefer Preincrement</a></li>
54 <li><a href="#ll_avoidendl">Avoid <tt>std::endl</tt></a></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]55 </ol></li>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]56 </ol></li>
57 <li><a href="#seealso">See Also</a></li>
58</ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]59
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]60<div class="doc_author">
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]61 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a> and
62 <a href="mailto:void@nondot.org">Bill Wendling</a></p>
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]63</div>
64
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]65
66<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]67<div class="doc_section">
68 <a name="introduction">Introduction</a>
69</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]70<!-- *********************************************************************** -->
71
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]72<div class="doc_text">
73
74<p>This document attempts to describe a few coding standards that are being used
75in the LLVM source tree. Although no coding standards should be regarded as
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]76absolute requirements to be followed in all instances, coding standards can be
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]77useful.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]78
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]79<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]80issues such as brace placement and space usage. For issues like this, follow
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]81the golden rule:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]82
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]83<blockquote>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]84
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]85<p><b><a name="goldenrule">If you are adding a significant body of source to a
86project, feel free to use whatever style you are most comfortable with. If you
87are extending, enhancing, or bug fixing already implemented code, use the style
88that is already being used so that the source is uniform and easy to
89follow.</a></b></p>
90
91</blockquote>
92
93<p>The ultimate goal of these guidelines is the increase readability and
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]94maintainability of our common source base. If you have suggestions for topics to
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]95be included, please mail them to <a
96href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]97
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]98</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]99
100<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]101<div class="doc_section">
102 <a name="mechanicalissues">Mechanical Source Issues</a>
103</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]104<!-- *********************************************************************** -->
105
106<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]107<div class="doc_subsection">
108 <a name="sourceformating">Source Code Formatting</a>
109</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]110
111<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]112<div class="doc_subsubsection">
113 <a name="scf_commenting">Commenting</a>
114</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]115
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]116<div class="doc_text">
117
118<p>Comments are one critical part of readability and maintainability. Everyone
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]119knows they should comment, so should you. Although we all should probably
Misha Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]120comment our code more than we do, there are a few very critical places that
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]121documentation is very useful:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]122
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]123<b>File Headers</b>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]124
125<p>Every source file should have a header on it that
126describes the basic purpose of the file. If a file does not have a header, it
127should not be checked into CVS. Most source trees will probably have a standard
128file header format. The standard format for the LLVM source tree looks like
129this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]130
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]131<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]132<pre>
Chris Lattnerc49fcd12003-10-13 14:58:11 +0000[diff] [blame]133//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]134//
135// The LLVM Compiler Infrastructure
136//
Chris Lattner4f28a2f2007-02-19 03:33:06 +0000[diff] [blame]137// This file was developed by &lt;whoever started the file&gt; and is distributed under
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]138// the University of Illinois Open Source License. See LICENSE.TXT for details.
139//
140//===----------------------------------------------------------------------===//
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]141//
142// This file contains the declaration of the Instruction class, which is the
143// base class for all of the VM instructions.
144//
145//===----------------------------------------------------------------------===//
146</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]147</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]148
Chris Lattner4f28a2f2007-02-19 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]152-*-</tt>" string on the first line is there to tell Emacs that the source file
Misha Brukman69c58892004-07-28 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]158
Chris Lattner999cf092004-05-23 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 Brukman75f258e2003-10-24 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 Brukman1b36d672003-10-06 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]166included, as well as any notes or "gotchas" in the code to watch out for.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]167
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]168<b>Class overviews</b>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]169
Jim Laskeyf55914a2006-07-31 20:18:49 +0000[diff] [blame]170<p>Classes are one fundamental part of a good object oriented design. As such,
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]171a class definition should have a comment block that explains what the class is
Misha Brukman1b36d672003-10-06 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 Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]174something sane goes a long ways towards avoiding writing documentation.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]175
176
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]177<b>Method information</b>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]178
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]179<p>Methods defined in a class (as well as any global functions) should also be
Misha Brukman1b36d672003-10-06 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]184the goal metric.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]185
Misha Brukman75f258e2003-10-24 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]189</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]190
191<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]192<div class="doc_subsubsection">
193 <a name="scf_commentformat">Comment Formatting</a>
194</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]195
Misha Brukman75f258e2003-10-24 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 Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]199require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]200when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]201
202<ol>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]203 <li>When writing a C code: Obviously if you are writing C code, use C style
Misha Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]204 comments.</li>
Misha Brukman91d64af2004-10-26 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 Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]210
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]215
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]216<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]217<div class="doc_subsubsection">
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]218 <a name="scf_includes"><tt>#include</tt> Style</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]219</div>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]220
Misha Brukman75f258e2003-10-24 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 Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]224include guards if working on a header file), the <a
Misha Brukmana8c760a2004-07-28 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 Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]228
229<ol>
Misha Brukman75f258e2003-10-24 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 Brukmana8c760a2004-07-28 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]237 <li>...</li>
Misha Brukmana8c760a2004-07-28 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 Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]241</ol>
242
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]243<p>... and each catagory should be sorted by name.</p>
Chris Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]244
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]245<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
Misha Brukman91d64af2004-10-26 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 Lattner2e5cbc22003-08-07 21:45:47 +0000[diff] [blame]253
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]254</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]255
256<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]257<div class="doc_subsubsection">
258 <a name="scf_codewidth">Source Code Width</a>
259</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]260
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]261<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]262
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]268
269<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]273
Misha Brukman75f258e2003-10-24 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 Brukman1b36d672003-10-06 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]280unreadable, and it is not worth dealing with.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]281
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]282<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman1b36d672003-10-06 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]286makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]287
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]288</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]289
290<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]291<div class="doc_subsubsection">
292 <a name="scf_indentation">Indent Code Consistently</a>
293</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]294
Misha Brukman75f258e2003-10-24 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 Brukman1b36d672003-10-06 19:26:00 +0000[diff] [blame]298important. If you didn't believe and internalize this then, now is the time.
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]299Just do it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]300
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]301</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]302
303
304<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]305<div class="doc_subsection">
306 <a name="compilerissues">Compiler Issues</a>
307</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]308
309
310<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]314
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]315<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]316
Misha Brukman75f258e2003-10-24 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 Brukman1b36d672003-10-06 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]328I write code like this:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]329
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]330<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]331<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]332if (V = getValue()) {
333 ...
334}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]335</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]336</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]337
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]342
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]343<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]344<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]345if ((V = getValue())) {
346 ...
347}
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]348</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]349</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]350
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]353
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]356
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]357</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]358
359<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]360<div class="doc_subsubsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]361 <a name="ci_portable_code">Write Portable Code</a>
362</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]363
Misha Brukman75f258e2003-10-24 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 Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]367portable code. If there are cases where it isn't possible to write portable
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]368code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]369
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]375
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]376</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]377
Reid Spencerb40df562004-09-23 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 Brukmanedcc78a2004-10-26 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 Spencerb40df562004-09-23 16:03:48 +0000[diff] [blame]396</div>
397
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]398<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]399<div class="doc_section">
400 <a name="styleissues">Style Issues</a>
401</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]402<!-- *********************************************************************** -->
403
404
405<!-- ======================================================================= -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]406<div class="doc_subsection">
407 <a name="macro">The High Level Issues</a>
408</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]409
410
411<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]415
Misha Brukman75f258e2003-10-24 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 Brukman2d10d752003-07-28 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]422module of functionality.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]423
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]424<p>Ideally, modules should be completely independent of each other, and their
Misha Brukman2d10d752003-07-28 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]430together.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]431
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]438
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]439</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]440
441<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]442<div class="doc_subsubsection">
Misha Brukman91d64af2004-10-26 16:18:43 +0000[diff] [blame]443 <a name="hl_dontinclude"><tt>#include</tt> as Little as Possible</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]444</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]445
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]446<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]447
Misha Brukman75f258e2003-10-24 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 Brukman91d64af2004-10-26 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]459
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]460<p>It is easy to try to go too overboard on this recommendation, however. You
Chris Lattner5da59b12007-02-10 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 Brukman2d10d752003-07-28 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]467about later...</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]468
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]469</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]470
471<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]472<div class="doc_subsubsection">
473 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
474</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]475
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]476<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]477
Misha Brukman75f258e2003-10-24 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 Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]481public module header file. Don't do this.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]482
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]486
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]491
Bill Wendling7f564c02006-12-09 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 Wendlingb0a9d1b2006-12-17 11:40:40 +0000[diff] [blame]515<table align="center">
Bill Wendling7f564c02006-12-09 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 Wendlingb0a9d1b2006-12-17 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 Wendling7f564c02006-12-09 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 Wendling0f7c10d2006-12-09 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 Wendlingb0a9d1b2006-12-17 11:40:40 +0000[diff] [blame]560void print(std::ostream *Out) { if (Out) print(*Out) }
Bill Wendling0f7c10d2006-12-09 01:27:51 +0000[diff] [blame]561// ...
Bill Wendlingb0a9d1b2006-12-17 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 Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]568</table>
569
570</div>
571
572
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]573<!-- ======================================================================= -->
Chris Lattner999cf092004-05-23 21:05:07 +0000[diff] [blame]574<div class="doc_subsection">
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]575 <a name="micro">The Low Level Issues</a>
576</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]577
578
579<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]580<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]581 <a name="ll_assert">Assert Liberally</a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]582</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]583
Misha Brukman75f258e2003-10-24 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 Brukman2d10d752003-07-28 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]591it.</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]592
Misha Brukman75f258e2003-10-24 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 Brukman2d10d752003-07-28 21:57:18 +0000[diff] [blame]595helps the poor debugging make sense of why an assertion is being made and
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]596enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]597
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]598<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]599<pre>
Misha Brukmana8c760a2004-07-28 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]604</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]605</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]606
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]607<p>Here are some examples:</p>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]608
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]609<div class="doc_code">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]610<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]611assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]612
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]613assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]614
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]615assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]616
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]617assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]618
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]619assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]620</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]621</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]622
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]623<p>You get the idea...</p>
624
625</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]626
Chris Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]627<!-- _______________________________________________________________________ -->
628<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]629 <a name="ll_ns_std">Do not use '<tt>using namespace std</tt>'</a>
Chris Lattnerb0bff9e2006-01-01 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 Wendling4ad6d612006-12-09 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 Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]636
Bill Wendling4ad6d612006-12-09 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 Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]640
Bill Wendling4ad6d612006-12-09 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 Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]650
Bill Wendling4ad6d612006-12-09 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 Lattnerb0bff9e2006-01-01 21:59:22 +0000[diff] [blame]659
660</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]661
662<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]663<div class="doc_subsubsection">
Bill Wendling4ad6d612006-12-09 01:35:43 +0000[diff] [blame]664 <a name="ll_virtual_anch">Provide a virtual method anchor for classes
665 in headers</a>
Chris Lattner6883a882006-07-27 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]683</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]684
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]685<div class="doc_text">
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]686
Misha Brukmana8c760a2004-07-28 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]690
691<p>The semantics of postincrement include making a copy of the value being
Misha Brukman2d10d752003-07-28 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 Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]699
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]700<!-- _______________________________________________________________________ -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]701<div class="doc_subsubsection">
Chris Lattner6883a882006-07-27 04:24:14 +0000[diff] [blame]702 <a name="ll_avoidendl">Avoid <tt>std::endl</tt></a>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]703</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]704
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]705<div class="doc_text">
706
Chris Lattner999cf092004-05-23 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 Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]710
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]711<div class="doc_code">
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]712<pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]713std::cout &lt;&lt; std::endl;
714std::cout &lt;&lt; '\n' &lt;&lt; std::flush;
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]715</pre>
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]716</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]717
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]718<p>Most of the time, you probably have no reason to flush the output stream, so
Misha Brukmana8c760a2004-07-28 22:31:54 +0000[diff] [blame]719it's better to use a literal <tt>'\n'</tt>.</p>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]720
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]721</div>
Chris Lattner13c46592002-01-20 19:01:26 +0000[diff] [blame]722
Bill Wendling7f564c02006-12-09 01:20:34 +0000[diff] [blame]723
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]724<!-- *********************************************************************** -->
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]725<div class="doc_section">
726 <a name="seealso">See Also</a>
727</div>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]728<!-- *********************************************************************** -->
729
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]734
735<ol>
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]736
Tanya Lattner09cf73c2004-06-22 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 Brukman75f258e2003-10-24 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 Lattner999cf092004-05-23 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]743
Misha Brukman75f258e2003-10-24 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 Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]746
Misha Brukman75f258e2003-10-24 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 Brukman3b53a262004-12-04 00:32:12 +0000[diff] [blame]750something.</p>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]751
752</div>
753
Chris Lattnerd80c43c2001-07-09 03:27:08 +0000[diff] [blame]754<!-- *********************************************************************** -->
755
756<hr>
Misha Brukman6c16c4b2004-05-12 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 Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]762
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]763 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
Reid Spencer05fe4b02006-03-14 05:39:39 +0000[diff] [blame]764 <a href="http://llvm.org">LLVM Compiler Infrastructure</a><br>
Misha Brukman75f258e2003-10-24 17:57:33 +0000[diff] [blame]765 Last modified: $Date$
Misha Brukman6c16c4b2004-05-12 18:37:22 +0000[diff] [blame]766</address>
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