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gerrit-public.fairphone.software / toolchain / llvm-project / 2361fcff41581bc3ef2c4e52ae970c3a153bed83 / . / llvm / docs / CodingStandards.html
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4<head>
5 <link rel="stylesheet" href="llvm.css" type="text/css">
6 <title>A Few Coding Standards</title>
7</head>
8<body>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]9
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]10<div class="doc_title">
11 A Few Coding Standards
12</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]13
14<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]15 <li><a href="#introduction">Introduction</a></li>
Chris Lattner85014f42001-07-23 20:40:41 +0000[diff] [blame]16 <li><a href="#mechanicalissues">Mechanical Source Issues</a>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]17 <ol>
18 <li><a href="#sourceformating">Source Code Formatting</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]19 <ol>
20 <li><a href="#scf_commenting">Commenting</a></li>
21 <li><a href="#scf_commentformat">Comment Formatting</a></li>
22 <li><a href="#scf_includes">#include Style</a></li>
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>
32 </ol></li>
33 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]34 <li><a href="#styleissues">Style Issues</a>
35 <ol>
36 <li><a href="#macro">The High Level Issues</a>
37 <ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]38 <li><a href="#hl_module">A Public Header File <b>is</b> a
39 Module</a></li>
40 <li><a href="#hl_dontinclude">#include as Little as Possible</a></li>
41 <li><a href="#hl_privateheaders">Keep "internal" Headers
42 Private</a></li>
43 </ol></li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]44 <li><a href="#micro">The Low Level Issues</a>
45 <ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]46 <li><a href="#hl_assert">Assert Liberally</a></li>
47 <li><a href="#hl_preincrement">Prefer Preincrement</a></li>
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]48 <li><a href="#hl_avoidendl">Avoid std::endl</a></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]49 <li><a href="#hl_exploitcpp">Exploit C++ to its Fullest</a></li>
50 </ol></li>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]51 </ol></li>
52 <li><a href="#seealso">See Also</a></li>
53</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]54
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]55<div class="doc_author">
56 <p>Written by <a href="mailto:sabre@nondot.org">Chris Lattner</a></p>
57</div>
58
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]59
60<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]61<div class="doc_section">
62 <a name="introduction">Introduction</a>
63</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]64<!-- *********************************************************************** -->
65
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]66<div class="doc_text">
67
68<p>This document attempts to describe a few coding standards that are being used
69in the LLVM source tree. Although no coding standards should be regarded as
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]70absolute requirements to be followed in all instances, coding standards can be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]71useful.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]72
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]73<p>This document intentionally does not prescribe fixed standards for religious
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]74issues such as brace placement and space usage. For issues like this, follow
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]75the golden rule:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]76
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]77<blockquote>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]78
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]79<p><b><a name="goldenrule">If you are adding a significant body of source to a
80project, feel free to use whatever style you are most comfortable with. If you
81are extending, enhancing, or bug fixing already implemented code, use the style
82that is already being used so that the source is uniform and easy to
83follow.</a></b></p>
84
85</blockquote>
86
87<p>The ultimate goal of these guidelines is the increase readability and
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]88maintainability of our common source base. If you have suggestions for topics to
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]89be included, please mail them to <a
90href="mailto:sabre@nondot.org">Chris</a>.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]91
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]92</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]93
94<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]95<div class="doc_section">
96 <a name="mechanicalissues">Mechanical Source Issues</a>
97</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]98<!-- *********************************************************************** -->
99
100<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]101<div class="doc_subsection">
102 <a name="sourceformating">Source Code Formatting</a>
103</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]104
105<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]106<div class="doc_subsubsection">
107 <a name="scf_commenting">Commenting</a>
108</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]109
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]110<div class="doc_text">
111
112<p>Comments are one critical part of readability and maintainability. Everyone
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]113knows they should comment, so should you. :) Although we all should probably
114comment our code more than we do, there are a few very critical places that
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]115documentation is very useful:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]116
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]117<b>File Headers</b>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]118
119<p>Every source file should have a header on it that
120describes the basic purpose of the file. If a file does not have a header, it
121should not be checked into CVS. Most source trees will probably have a standard
122file header format. The standard format for the LLVM source tree looks like
123this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]124
125<pre>
Chris Lattnere6f4e072003-10-13 14:58:11 +0000[diff] [blame]126//===-- llvm/Instruction.h - Instruction class definition -------*- C++ -*-===//
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]127//
128// The LLVM Compiler Infrastructure
129//
130// This file was developed by the LLVM research group and is distributed under
131// the University of Illinois Open Source License. See LICENSE.TXT for details.
132//
133//===----------------------------------------------------------------------===//
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]134//
135// This file contains the declaration of the Instruction class, which is the
136// base class for all of the VM instructions.
137//
138//===----------------------------------------------------------------------===//
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]139
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]140</pre>
141
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]142<p>A few things to note about this particular format: The "<tt>-*- C++
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]143-*-</tt>" string on the first line is there to tell Emacs that the source file
144is a C++ file, not a C file (Emacs assumes .h files are C files by default [Note
145that tag this is not necessary in .cpp files]). The name of the file is also on
146the first line, along with a very short description of the purpose of the file.
147This is important when printing out code and flipping though lots of pages.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]148
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]149<p>The next section in the file is a concise note that defines the license that
150the file is released under. This makes it perfectly clear what terms the source
151code can be distributed under.</p>
152
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]153<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]154Here it's only two lines. If an algorithm is being implemented or something
155tricky is going on, a reference to the paper where it is published should be
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]156included, 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]157
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]158<b>Class overviews</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]159
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]160<p>Classes are one fundemental part of a good object oriented design. As such,
161a class definition should have a comment block that explains what the class is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]162used for... if it's not obvious. If it's so completely obvious your grandma
163could figure it out, it's probably safe to leave it out. Naming classes
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]164something sane goes a long ways towards avoiding writing documentation. :)</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]165
166
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]167<b>Method information</b>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]168
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]169<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]170documented properly. A quick note about what it does any a description of the
171borderline behaviour is all that is necessary here (unless something
172particularly tricky or insideous is going on). The hope is that people can
173figure out how to use your interfaces without reading the code itself... that is
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]174the goal metric.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]175
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]176<p>Good things to talk about here are what happens when something unexpected
177happens: does the method return null? Abort? Format your hard disk?</p>
178
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]179</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]180
181<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]182<div class="doc_subsubsection">
183 <a name="scf_commentformat">Comment Formatting</a>
184</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]185
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]186<div class="doc_text">
187
188<p>In general, prefer C++ style (<tt>//</tt>) comments. They take less space,
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]189require less typing, don't have nesting problems, etc. There are a few cases
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]190when it is useful to use C style (<tt>/* */</tt>) comments however:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]191
192<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]193 <li>When writing a C code: Obviously if you are writing C code, use C style
194 comments. :)</li>
195 <li>When writing a header file that may be #included by a C source file.</li>
196 <li>When writing a source file that is used by a tool that only accepts C
197 style comments.</li>
198</ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]199
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]200<p>To comment out a large block of code, use <tt>#if 0</tt> and <tt>#endif</tt>.
201These nest properly and are better behaved in general than C style comments.</p>
202
203</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]204
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]205<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]206<div class="doc_subsubsection">
207 <a name="scf_includes">#include Style</a>
208</div>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]209
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]210<div class="doc_text">
211
212<p>Immediately after the <a href="#scf_commenting">header file comment</a> (and
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]213include guards if working on a header file), the <a
Misha Brukman31551592004-06-03 23:42:24 +0000[diff] [blame]214href="#hl_dontinclude">minimal</a> list of #includes required by the file should
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]215be listed. We prefer these #includes to be listed in this order:</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]216
217<ol>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]218 <li><a href="#mmheader">Main Module header</a></li>
219 <li><a href="#hl_privateheaders">Local/Private Headers</a></li>
220 <li>llvm/*</li>
221 <li>llvm/Analysis/*</li>
222 <li>llvm/Assembly/*</li>
223 <li>llvm/Bytecode/*</li>
224 <li>llvm/CodeGen/*</li>
225 <li>...</li>
226 <li>Support/*</li>
227 <li>Config/*</li>
228 <li>System #includes</li>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]229</ol>
230
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]231<p>... and each catagory should be sorted by name.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]232
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]233<p><a name="mmheader">The "Main Module Header"</a> file applies to .cpp file
234which implement an interface defined by a .h file. This #include should always
235be included <b>first</b> regardless of where it lives on the file system. By
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]236including a header file first in the .cpp files that implement the interfaces,
237we ensure that the header does not have any hidden dependencies which are not
238explicitly #included in the header, but should be. It is also a form of
239documentation in the .cpp file to indicate where the interfaces it implements
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]240are defined.</p>
Chris Lattner245b5252003-08-07 21:45:47 +0000[diff] [blame]241
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]242</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]243
244<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]245<div class="doc_subsubsection">
246 <a name="scf_codewidth">Source Code Width</a>
247</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]248
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]249<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]250
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]251<p>Write your code to fit within 80 columns of text. This helps those of us who
252like to print out code and look at your code in an xterm without resizing
253it.</p>
254
255</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]256
257<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]258<div class="doc_subsubsection">
259 <a name="scf_spacestabs">Use Spaces Instead of Tabs</a>
260</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]261
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]262<div class="doc_text">
263
264<p>In all cases, prefer spaces to tabs in source files. People have different
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]265prefered indentation levels, and different styles of indentation that they
266like... this is fine. What isn't is that different editors/viewers expand tabs
267out to different tab stops. This can cause your code to look completely
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]268unreadable, and it is not worth dealing with.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]269
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]270<p>As always, follow the <a href="#goldenrule">Golden Rule</a> above: follow the
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]271style of existing code if your are modifying and extending it. If you like four
272spaces of indentation, <b>DO NOT</b> do that in the middle of a chunk of code
273with two spaces of indentation. Also, do not reindent a whole source file: it
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]274makes for incredible diffs that are absolutely worthless.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]275
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]276</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]277
278<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]279<div class="doc_subsubsection">
280 <a name="scf_indentation">Indent Code Consistently</a>
281</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]282
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]283<div class="doc_text">
284
285<p>Okay, your first year of programming you were told that indentation is
Misha Brukman0cedb1f2003-10-06 19:26:00 +0000[diff] [blame]286important. If you didn't believe and internalize this then, now is the time.
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]287Just do it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]288
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]289</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]290
291
292<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]293<div class="doc_subsection">
294 <a name="compilerissues">Compiler Issues</a>
295</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]296
297
298<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]299<div class="doc_subsubsection">
300 <a name="ci_warningerrors">Treat Compiler Warnings Like Errors</a>
301</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]302
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]303<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]304
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]305<p>If your code has compiler warnings in it, something is wrong: you aren't
306casting values correctly, your have "questionable" constructs in your code, or
307you are doing something legitimately wrong. Compiler warnings can cover up
308legitimate errors in output and make dealing with a translation unit
309difficult.</p>
310
311<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]312desirable. Instead, pick a standard compiler (like <tt>gcc</tt>) that provides
313a good thorough set of warnings, and stick to them. At least in the case of
314<tt>gcc</tt>, it is possible to work around any spurious errors by changing the
315syntax of the code slightly. For example, an warning that annoys me occurs when
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]316I write code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]317
318<pre>
319 if (V = getValue()) {
320 ..
321 }
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]322</pre>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]323
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]324<p><tt>gcc</tt> will warn me that I probably want to use the <tt>==</tt>
325operator, and that I probably mistyped it. In most cases, I haven't, and I
326really don't want the spurious errors. To fix this particular problem, I
327rewrite the code like this:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]328
329<pre>
330 if ((V = getValue())) {
331 ..
332 }
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]333</pre>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]334
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]335<p>...which shuts <tt>gcc</tt> up. Any <tt>gcc</tt> warning that annoys you can
336be fixed by massaging the code appropriately.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]337
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]338<p>These are the <tt>gcc</tt> warnings that I prefer to enable: <tt>-Wall
339-Winline -W -Wwrite-strings -Wno-unused</tt></p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]340
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]341</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]342
343<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]344<div class="doc_subsubsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]345 <a name="ci_portable_code">Write Portable Code</a>
346</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]347
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]348<div class="doc_text">
349
350<p>In almost all cases, it is possible and within reason to write completely
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]351portable code. If there are cases where it isn't possible to write portable
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]352code, isolate it behind a well defined (and well documented) interface.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]353
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]354<p>In practice, this means that you shouldn't assume much about the host
355compiler, including its support for "high tech" features like partial
356specialization of templates. In fact, Visual C++ 6 could be an important target
357for our work in the future, and we don't want to have to rewrite all of our code
358to support it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]359
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]360</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]361
362<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]363<div class="doc_section">
364 <a name="styleissues">Style Issues</a>
365</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]366<!-- *********************************************************************** -->
367
368
369<!-- ======================================================================= -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]370<div class="doc_subsection">
371 <a name="macro">The High Level Issues</a>
372</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]373
374
375<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]376<div class="doc_subsubsection">
377 <a name="hl_module">A Public Header File <b>is</b> a Module</a>
378</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]379
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]380<div class="doc_text">
381
382<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]383encapsulation or data hiding (unless you use expensive protocol classes), but it
384is what we have to work with. When you write a public header file (in the LLVM
385source tree, they live in the top level "include" directory), you are defining a
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]386module of functionality.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]387
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]388<p>Ideally, modules should be completely independent of each other, and their
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]389header files should only include the absolute minimum number of headers
390possible. A module is not just a class, a function, or a namespace: <a
391href="http://www.cuj.com/articles/2000/0002/0002c/0002c.htm">it's a collection
392of these</a> that defines an interface. This interface may be several
393functions, classes or data structures, but the important issue is how they work
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]394together.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]395
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]396<p>In general, a module should be implemented with one or more <tt>.cpp</tt>
397files. Each of these <tt>.cpp</tt> files should include the header that defines
398their interface first. This ensure that all of the dependences of the module
399header have been properly added to the module header itself, and are not
400implicit. System headers should be included after user headers for a
401translation unit.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]402
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]403</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]404
405<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]406<div class="doc_subsubsection">
407 <a name="hl_dontinclude">#include as Little as Possible</a>
408</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]409
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]410<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]411
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]412<p><tt>#include</tt> hurts compile time performance. Don't do it unless you
413have to, especially in header files.</p>
414
415<p>But wait, sometimes you need to have the definition of a class to use it, or
416to inherit from it. In these cases go ahead and #include that header file. Be
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]417aware however that there are many cases where you don't need to have the full
418definition of a class. If you are using a pointer or reference to a class, you
419don't need the header file. If you are simply returning a class instance from a
420prototyped function or method, you don't need it. In fact, for most cases, you
421simply don't need the definition of a class... and not <tt>#include</tt>'ing
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]422speeds up compilation.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]423
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]424<p>It is easy to try to go too overboard on this recommendation, however. You
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]425<b>must</b> include all of the header files that you are using, either directly
426or indirectly (through another header file). To make sure that you don't
427accidently forget to include a header file in your module header, make sure to
428include your module header <b>first</b> in the implementation file (as mentioned
429above). This way there won't be any hidden dependencies that you'll find out
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]430about later...</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]431
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]432</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]433
434<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]435<div class="doc_subsubsection">
436 <a name="hl_privateheaders">Keep "internal" Headers Private</a>
437</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]438
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]439<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]440
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]441<p>Many modules have a complex implementation that causes them to use more than
442one implementation (<tt>.cpp</tt>) file. It is often tempting to put the
443internal communication interface (helper classes, extra functions, etc) in the
444public module header file. Don't do this. :)</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]445
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]446<p>If you really need to do something like this, put a private header file in
447the same directory as the source files, and include it locally. This ensures
448that your private interface remains private and undisturbed by outsiders.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]449
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]450<p>Note however, that it's okay to put extra implementation methods a public
451class itself... just make them private (or protected), and all is well.</p>
452
453</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]454
455<!-- ======================================================================= -->
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]456<div class="doc_subsection">
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]457 <a name="micro">The Low Level Issues</a>
458</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]459
460
461<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]462<div class="doc_subsubsection">
463 <a name="hl_assert">Assert Liberally</a>
464</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]465
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]466<div class="doc_text">
467
468<p>Use the "<tt>assert</tt>" function to its fullest. Check all of your
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]469preconditions and assumptions, you never know when a bug (not neccesarily even
470yours) might be caught early by an assertion, which reduces debugging time
471dramatically. The "<tt>&lt;cassert&gt;</tt>" header file is probably already
472included 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]473it.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]474
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]475<p>To further assist with debugging, make sure to put some kind of error message
476in the assertion statement (which is printed if the assertion is tripped). This
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]477helps the poor debugging make sense of why an assertion is being made and
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]478enforced, and hopefully what to do about it. Here is one complete example:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]479
480<pre>
481 inline Value *getOperand(unsigned i) {
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]482 assert(i &lt; Operands.size() &amp;&amp; "getOperand() out of range!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]483 return Operands[i];
484 }
485</pre>
486
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]487<p>Here are some examples:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]488
489<pre>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]490 assert(Ty-&gt;isPointerType() &amp;&amp; "Can't allocate a non pointer type!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]491
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]492 assert((Opcode == Shl || Opcode == Shr) &amp;&amp; "ShiftInst Opcode invalid!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]493
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]494 assert(idx &lt; getNumSuccessors() &amp;&amp; "Successor # out of range!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]495
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]496 assert(V1.getType() == V2.getType() &amp;&amp; "Constant types must be identical!");
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]497
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]498 assert(isa&lt;PHINode&gt;(Succ-&gt;front()) &amp;&amp; "Only works on PHId BBs!");
499</pre>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]500
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]501<p>You get the idea...</p>
502
503</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]504
505
506<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]507<div class="doc_subsubsection">
508 <a name="hl_preincrement">Prefer Preincrement</a>
509</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]510
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]511<div class="doc_text">
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]512
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]513<p>Hard fast rule: Preincrement (++X) may be no slower than postincrement (X++)
514and could very well be a lot faster than it. Use preincrementation whenever
515possible.</p>
516
517<p>The semantics of postincrement include making a copy of the value being
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]518incremented, returning it, and then preincrementing the "work value". For
519primitive types, this isn't a big deal... but for iterators, it can be a huge
520issue (for example, some iterators contains stack and set objects in them...
521copying an iterator could invoke the copy ctor's of these as well). In general,
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]522get in the habit of always using preincrement, and you won't have a problem.</p>
523
524</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]525
526
527<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]528<div class="doc_subsubsection">
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]529 <a name="hl_avoidendl">Avoid std::endl</a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]530</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]531
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]532<div class="doc_text">
533
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]534<p>The <tt>std::endl</tt> modifier, when used with iostreams outputs a newline
535to the output stream specified. In addition to doing this, however, it also
536flushes the output stream. In other words, these are equivalent:</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]537
538<pre>
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]539 std::cout &lt;&lt; std::endl;
540 std::cout &lt;&lt; "\n" &lt;&lt; std::flush;
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]541</pre>
542
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]543<p>Most of the time, you probably have no reason to flush the output stream, so
544it's better to use a literal <tt>"\n"</tt>.</p>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]545
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]546</div>
Chris Lattner850d4f62002-01-20 19:01:26 +0000[diff] [blame]547
548<!-- _______________________________________________________________________ -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]549<div class="doc_subsubsection">
550 <a name="hl_exploitcpp">Exploit C++ to its Fullest</a>
551</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]552
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]553<div class="doc_text">
554
555<p>C++ is a powerful language. With a firm grasp on its capabilities, you can make
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]556write effective, consise, readable and maintainable code all at the same time.
557By staying consistent, you reduce the amount of special cases that need to be
558remembered. Reducing the total number of lines of code you write is a good way
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]559to avoid documentation, and avoid giving bugs a place to hide.</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]560
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]561<p>For these reasons, come to know and love the contents of your local
Misha Brukmanc3e78932003-07-28 21:57:18 +0000[diff] [blame]562&lt;algorithm&gt; header file. Know about &lt;functional&gt; and what it can do
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]563for you. C++ is just a tool that wants you to master it. :)</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]564
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]565</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]566
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]567<!-- *********************************************************************** -->
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]568<div class="doc_section">
569 <a name="seealso">See Also</a>
570</div>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]571<!-- *********************************************************************** -->
572
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]573<div class="doc_text">
574
575<p>A lot of these comments and recommendations have been culled for other
576sources. Two particularly important books for our work are:</p>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]577
578<ol>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]579
Tanya Lattner8ed32be2004-06-22 04:24:55 +0000[diff] [blame]580<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]581C++</a> by Scott Meyers. There is an online version of the book (only some
582chapters though) <a
Chris Lattner1dab1922004-05-23 21:05:07 +0000[diff] [blame]583href="http://www.awlonline.com/cseng/meyerscddemo/">available as well</a>. Also
584interesting and useful are "More Effective C++" and "Effective STL" by the same
585author.</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]586
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]587<li><a href="http://cseng.aw.com/book/0,3828,0201633620,00.html">Large-Scale C++
588Software Design</a> by John Lakos</li>
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]589
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]590</ol>
591
592<p>If you get some free time, and you haven't read them: do so, you might learn
593something. :)</p>
594
595</div>
596
Chris Lattnerac457c42001-07-09 03:27:08 +0000[diff] [blame]597<!-- *********************************************************************** -->
598
599<hr>
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]600<address>
601 <a href="http://jigsaw.w3.org/css-validator/check/referer"><img
602 src="http://jigsaw.w3.org/css-validator/images/vcss" alt="Valid CSS!"></a>
603 <a href="http://validator.w3.org/check/referer"><img
604 src="http://www.w3.org/Icons/valid-html401" alt="Valid HTML 4.01!"></a>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]605
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]606 <a href="mailto:sabre@nondot.org">Chris Lattner</a><br>
607 <a href="http://llvm.cs.uiuc.edu">LLVM Compiler Infrastructure</a><br>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]608 Last modified: $Date$
Misha Brukmand4f290a2004-05-12 18:37:22 +0000[diff] [blame]609</address>
Misha Brukmanf196dbb2003-10-24 17:57:33 +0000[diff] [blame]610
611</body>
612</html>