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4<head>
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]5 <meta http-equiv="content-type" content="text/html; charset=iso-8859-1">
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]6 <title>Clang - Expressive Diagnostics</title>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]7 <link type="text/css" rel="stylesheet" href="menu.css">
8 <link type="text/css" rel="stylesheet" href="content.css">
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]9 <style type="text/css">
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]10 .warn { color:magenta; }
11 .err { color:red; }
12 .snip { color:darkgreen; }
13 .point { color:blue; }
14 </style>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]15</head>
16<body>
17
18<!--#include virtual="menu.html.incl"-->
19
20<div id="content">
21
22
23<!--=======================================================================-->
24<h1>Expressive Diagnostics</h1>
25<!--=======================================================================-->
26
27<p>In addition to being fast and functional, we aim to make Clang extremely user
28friendly. As far as a command-line compiler goes, this basically boils down to
29making the diagnostics (error and warning messages) generated by the compiler
30be as useful as possible. There are several ways that we do this. This section
31talks about the experience provided by the command line compiler, contrasting
32Clang output to GCC 4.2's output in several examples.
33<!--
34Other clients
35that embed Clang and extract equivalent information through internal APIs.-->
36</p>
37
38<h2>Column Numbers and Caret Diagnostics</h2>
39
40<p>First, all diagnostics produced by clang include full column number
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]41information. The clang command-line compiler driver uses this information
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]42to print "point diagnostics".
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]43(IDEs can use the information to display in-line error markup.)
44Precise error location in the source is a feature provided by many commercial
45compilers, but is generally missing from open source
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]46compilers. This is nice because it makes it very easy to understand exactly
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]47what is wrong in a particular piece of code</p>
48
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]49<p>The point (the blue "^" character) exactly shows where the problem is, even
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]50inside of a string. This makes it really easy to jump to the problem and
51helps when multiple instances of the same character occur on a line. (We'll
52revisit this more in following examples.)</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]53
54<pre>
55 $ <b>gcc-4.2 -fsyntax-only -Wformat format-strings.c</b>
56 format-strings.c:91: warning: too few arguments for format
57 $ <b>clang -fsyntax-only format-strings.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]58 format-strings.c:91:13: <span class="warn">warning:</span> '.*' specified field precision is missing a matching 'int' argument
59 <span class="snip"> printf("%.*d");</span>
60 <span class="point"> ^</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]61</pre>
62
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]63<h2>Range Highlighting for Related Text</h2>
64
65<p>Clang captures and accurately tracks range information for expressions,
66statements, and other constructs in your program and uses this to make
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]67diagnostics highlight related information. In the following somewhat
68nonsensical example you can see that you don't even need to see the original source code to
69understand what is wrong based on the Clang error. Because clang prints a
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]70point, you know exactly <em>which</em> plus it is complaining about. The range
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]71information highlights the left and right side of the plus which makes it
72immediately obvious what the compiler is talking about.
73Range information is very useful for
74cases involving precedence issues and many other cases.</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]75
76<pre>
77 $ <b>gcc-4.2 -fsyntax-only t.c</b>
78 t.c:7: error: invalid operands to binary + (have 'int' and 'struct A')
79 $ <b>clang -fsyntax-only t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]80 t.c:7:39: <span class="err">error:</span> invalid operands to binary expression ('int' and 'struct A')
81 <span class="snip"> return y + func(y ? ((SomeA.X + 40) + SomeA) / 42 + SomeA.X : SomeA.X);</span>
82 <span class="point"> ~~~~~~~~~~~~~~ ^ ~~~~~</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]83</pre>
84
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]85<h2>Precision in Wording</h2>
86
87<p>A detail is that we have tried really hard to make the diagnostics that come
88out of clang contain exactly the pertinent information about what is wrong and
89why. In the example above, we tell you what the inferred types are for
90the left and right hand sides, and we don't repeat what is obvious from the
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]91point (e.g., that this is a "binary +").</p>
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]92
93<p>Many other examples abound. In the following example, not only do we tell you that there is a problem with the *
94and point to it, we say exactly why and tell you what the type is (in case it is
95a complicated subexpression, such as a call to an overloaded function). This
96sort of attention to detail makes it much easier to understand and fix problems
97quickly.</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]98
99<pre>
100 $ <b>gcc-4.2 -fsyntax-only t.c</b>
101 t.c:5: error: invalid type argument of 'unary *'
102 $ <b>clang -fsyntax-only t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]103 t.c:5:11: <span class="err">error:</span> indirection requires pointer operand ('int' invalid)
104 <span class="snip"> int y = *SomeA.X;</span>
105 <span class="point"> ^~~~~~~~</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]106</pre>
107
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]108<h2>No Pretty Printing of Expressions in Diagnostics</h2>
109
110<p>Since Clang has range highlighting, it never needs to pretty print your code
Chris Lattnerb3de1122011-08-03 15:54:40 +0000[diff] [blame]111back out to you. GCC can produce inscrutible error messages in some cases when
112it tries to do this. In this example P and Q have type "int*":</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]113
114<pre>
115 $ <b>gcc-4.2 -fsyntax-only t.c</b>
116 #'exact_div_expr' not supported by pp_c_expression#'t.c:12: error: called object is not a function
117 $ <b>clang -fsyntax-only t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]118 t.c:12:8: <span class="err">error:</span> called object type 'int' is not a function or function pointer
119 <span class="snip"> (P-Q)();</span>
120 <span class="point"> ~~~~~^</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]121</pre>
122
Chris Lattnerb3de1122011-08-03 15:54:40 +0000[diff] [blame]123<p>This can be particularly bad in G++, which often emits errors
124 containing lowered vtable references. For example:</p>
125
126<pre>
127 $ <b>cat t.cc</b>
128 struct a {
129 virtual int bar();
130 };
131
132 struct foo : public virtual a {
133 };
134
135 void test(foo *P) {
136 return P->bar() + *P;
137 }
138 $ <b>gcc-4.2 t.cc</b>
139 t.cc: In function 'void test(foo*)':
140 t.cc:9: error: no match for 'operator+' in '(((a*)P) + (*(long int*)(P-&gt;foo::&lt;anonymous&gt;.a::_vptr$a + -0x00000000000000020)))-&gt;a::bar() + * P'
141 t.cc:9: error: return-statement with a value, in function returning 'void'
142 $ <b>clang t.cc</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]143 t.cc:9:18: <span class="err">error:</span> invalid operands to binary expression ('int' and 'foo')
144 <span class="snip"> return P->bar() + *P;</span>
145 <span class="point"> ~~~~~~~~ ^ ~~</span>
Chris Lattnerb3de1122011-08-03 15:54:40 +0000[diff] [blame]146</pre>
147
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]148
149<h2>Typedef Preservation and Selective Unwrapping</h2>
150
151<p>Many programmers use high-level user defined types, typedefs, and other
152syntactic sugar to refer to types in their program. This is useful because they
153can abbreviate otherwise very long types and it is useful to preserve the
154typename in diagnostics. However, sometimes very simple typedefs can wrap
155trivial types and it is important to strip off the typedef to understand what
156is going on. Clang aims to handle both cases well.<p>
157
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]158<p>The following example shows where it is important to preserve
159a typedef in C. Here the type printed by GCC isn't even valid, but if the error
160were about a very long and complicated type (as often happens in C++) the error
161message would be ugly just because it was long and hard to read.</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]162
163<pre>
164 $ <b>gcc-4.2 -fsyntax-only t.c</b>
165 t.c:15: error: invalid operands to binary / (have 'float __vector__' and 'const int *')
166 $ <b>clang -fsyntax-only t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]167 t.c:15:11: <span class="err">error:</span> can't convert between vector values of different size ('__m128' and 'int const *')
168 <span class="snip"> myvec[1]/P;</span>
169 <span class="point"> ~~~~~~~~^~</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]170</pre>
171
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]172<p>The following example shows where it is useful for the compiler to expose
173underlying details of a typedef. If the user was somehow confused about how the
174system "pid_t" typedef is defined, Clang helpfully displays it with "aka".</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]175
176<pre>
177 $ <b>gcc-4.2 -fsyntax-only t.c</b>
178 t.c:13: error: request for member 'x' in something not a structure or union
179 $ <b>clang -fsyntax-only t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]180 t.c:13:9: <span class="err">error:</span> member reference base type 'pid_t' (aka 'int') is not a structure or union
181 <span class="snip"> myvar = myvar.x;</span>
182 <span class="point"> ~~~~~ ^</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]183</pre>
184
Douglas Gregor969c6892009-04-01 15:47:24 +0000[diff] [blame]185<p>In C++, type preservation includes retaining any qualification written into type names. For example, if we take a small snippet of code such as:
186
187<blockquote>
188<pre>
189namespace services {
190 struct WebService { };
191}
192namespace myapp {
193 namespace servers {
194 struct Server { };
195 }
196}
197
198using namespace myapp;
Benjamin Kramerd8ee4072011-08-06 03:04:45 +0000[diff] [blame]199void addHTTPService(servers::Server const &amp;server, ::services::WebService const *http) {
Douglas Gregor969c6892009-04-01 15:47:24 +0000[diff] [blame]200 server += http;
201}
202</pre>
203</blockquote>
204
205<p>and then compile it, we see that Clang is both providing more accurate information and is retaining the types as written by the user (e.g., "servers::Server", "::services::WebService"):
206
207<pre>
208 $ <b>g++-4.2 -fsyntax-only t.cpp</b>
209 t.cpp:9: error: no match for 'operator+=' in 'server += http'
210 $ <b>clang -fsyntax-only t.cpp</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]211 t.cpp:9:10: <span class="err">error:</span> invalid operands to binary expression ('servers::Server const' and '::services::WebService const *')
212 <span class="snip">server += http;</span>
213 <span class="point">~~~~~~ ^ ~~~~</span>
Douglas Gregor969c6892009-04-01 15:47:24 +0000[diff] [blame]214</pre>
215
216<p>Naturally, type preservation extends to uses of templates, and Clang retains information about how a particular template specialization (like <code>std::vector&lt;Real&gt;</code>) was spelled within the source code. For example:</p>
217
218<pre>
219 $ <b>g++-4.2 -fsyntax-only t.cpp</b>
220 t.cpp:12: error: no match for 'operator=' in 'str = vec'
221 $ <b>clang -fsyntax-only t.cpp</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]222 t.cpp:12:7: <span class="err">error:</span> incompatible type assigning 'vector&lt;Real&gt;', expected 'std::string' (aka 'class std::basic_string&lt;char&gt;')
223 <span class="snip">str = vec</span>;
224 <span class="point">^ ~~~</span>
Douglas Gregor969c6892009-04-01 15:47:24 +0000[diff] [blame]225</pre>
226
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]227<h2>Fix-it Hints</h2>
228
Douglas Gregoreff49c62009-04-01 16:24:40 +0000[diff] [blame]229<p>"Fix-it" hints provide advice for fixing small, localized problems
230in source code. When Clang produces a diagnostic about a particular
231problem that it can work around (e.g., non-standard or redundant
232syntax, missing keywords, common mistakes, etc.), it may also provide
233specific guidance in the form of a code transformation to correct the
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]234problem. In the following example, Clang warns about the use of a GCC
235extension that has been considered obsolete since 1993. The underlined
236code should be removed, then replaced with the code below the
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]237point line (".x =" or ".y =", respectively).</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]238
Douglas Gregoreff49c62009-04-01 16:24:40 +0000[diff] [blame]239<pre>
240 $ <b>clang t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]241 t.c:5:28: <span class="warn">warning:</span> use of GNU old-style field designator extension
242 <span class="snip">struct point origin = { x: 0.0, y: 0.0 };</span>
243 <span class="err">~~</span> <span class="point">^</span>
244 <span class="snip">.x = </span>
245 t.c:5:36: <span class="warn">warning:</span> use of GNU old-style field designator extension
246 <span class="snip">struct point origin = { x: 0.0, y: 0.0 };</span>
247 <span class="err">~~</span> <span class="point">^</span>
248 <span class="snip">.y = </span>
Douglas Gregoreff49c62009-04-01 16:24:40 +0000[diff] [blame]249</pre>
250
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]251<p>"Fix-it" hints are most useful for
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]252working around common user errors and misconceptions. For example, C++ users
253commonly forget the syntax for explicit specialization of class templates,
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]254as in the error in the following example. Again, after describing the problem,
255Clang provides the fix--add <code>template&lt;&gt;</code>--as part of the
256diagnostic.<p>
Douglas Gregoreff49c62009-04-01 16:24:40 +0000[diff] [blame]257
258<pre>
259 $ <b>clang t.cpp</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]260 t.cpp:9:3: <span class="err">error:</span> template specialization requires 'template&lt;&gt;'
Douglas Gregoreff49c62009-04-01 16:24:40 +0000[diff] [blame]261 struct iterator_traits&lt;file_iterator&gt; {
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]262 <span class="point">^</span>
263 <span class="snip">template&lt;&gt; </span>
Douglas Gregoreff49c62009-04-01 16:24:40 +0000[diff] [blame]264</pre>
265
Richard Trieue59331a2012-06-27 02:00:20 +0000[diff] [blame]266<h2>Template Type Diffing</h2>
267
268<p>Templates types can be long and difficult to read. Moreso when part of an
269error message. Instead of just printing out the type name, Clang has enough
270information to remove the common elements and highlight the differences. To
271show the template structure more clearly, the templated type can also be
272printed as an indented text tree.</p>
273
274Default: template diff with type elision
275<pre>
276t.cc:4:5: <span class="note">note:</span> candidate function not viable: no known conversion from 'vector&lt;map&lt;[...], <span class="template-highlight">float</span>&gt;&gt;' to 'vector&lt;map&lt;[...], <span class="template-highlight">double</span>&gt;&gt;' for 1st argument;
277</pre>
278-fno-elide-type: template diff without elision
279<pre>
280t.cc:4:5: <span class="note">note:</span> candidate function not viable: no known conversion from 'vector&lt;map&lt;int, <span class="template-highlight">float</span>&gt;&gt;' to 'vector&lt;map&lt;int, <span class="template-highlight">double</span>&gt;&gt;' for 1st argument;
281</pre>
282-fdiagnostics-show-template-tree: template tree printing with elision
283<pre>
284t.cc:4:5: <span class="note">note:</span> candidate function not viable: no known conversion for 1st argument;
285 vector&lt;
286 map&lt;
287 [...],
288 [<span class="template-highlight">float</span> != <span class="template-highlight">double</span>]&gt;&gt;
289</pre>
290-fdiagnostics-show-template-tree -fno-elide-type: template tree printing with no elision
291<pre>
292t.cc:4:5: <span class="note">note:M</span> candidate function not viable: no known conversion for 1st argument;
293 vector&lt;
294 map&lt;
295 int,
296 [<span class="template-highlight">float</span> != <span class="template-highlight">double</span>]&gt;&gt;
297</pre>
298
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]299<h2>Automatic Macro Expansion</h2>
300
301<p>Many errors happen in macros that are sometimes deeply nested. With
302traditional compilers, you need to dig deep into the definition of the macro to
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]303understand how you got into trouble. The following simple example shows how
304Clang helps you out by automatically printing instantiation information and
305nested range information for diagnostics as they are instantiated through macros
306and also shows how some of the other pieces work in a bigger example.</p>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]307
308<pre>
309 $ <b>gcc-4.2 -fsyntax-only t.c</b>
310 t.c: In function 'test':
311 t.c:80: error: invalid operands to binary &lt; (have 'struct mystruct' and 'float')
312 $ <b>clang -fsyntax-only t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]313 t.c:80:3: <span class="err">error:</span> invalid operands to binary expression ('typeof(P)' (aka 'struct mystruct') and 'typeof(F)' (aka 'float'))
314 <span class="snip"> X = MYMAX(P, F);</span>
315 <span class="point"> ^~~~~~~~~~~</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]316 t.c:76:94: note: instantiated from:
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]317 <span class="snip">#define MYMAX(A,B) __extension__ ({ __typeof__(A) __a = (A); __typeof__(B) __b = (B); __a &lt; __b ? __b : __a; })</span>
318 <span class="point"> ~~~ ^ ~~~</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]319</pre>
320
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]321<p>Here's another real world warning that occurs in the "window" Unix package (which
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]322implements the "wwopen" class of APIs):</p>
323
324<pre>
325 $ <b>clang -fsyntax-only t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]326 t.c:22:2: <span class="warn">warning:</span> type specifier missing, defaults to 'int'
327 <span class="snip"> ILPAD();</span>
328 <span class="point"> ^</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]329 t.c:17:17: note: instantiated from:
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]330 <span class="snip">#define ILPAD() PAD((NROW - tt.tt_row) * 10) /* 1 ms per char */</span>
331 <span class="point"> ^</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]332 t.c:14:2: note: instantiated from:
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]333 <span class="snip"> register i; \</span>
334 <span class="point"> ^</span>
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]335</pre>
336
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]337<p>In practice, we've found that Clang's treatment of macros is actually more useful in multiply nested
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]338macros that in simple ones.</p>
339
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]340<h2>Quality of Implementation and Attention to Detail</h2>
341
342<p>Finally, we have put a lot of work polishing the little things, because
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]343little things add up over time and contribute to a great user experience.</p>
344
345<p>The following example shows a trivial little tweak, where we tell you to put the semicolon at
346the end of the line that is missing it (line 4) instead of at the beginning of
347the following line (line 5). This is particularly important with fixit hints
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]348and point diagnostics, because otherwise you don't get the important context.
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]349</p>
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]350
351<pre>
352 $ <b>gcc-4.2 t.c</b>
353 t.c: In function 'foo':
354 t.c:5: error: expected ';' before '}' token
355 $ <b>clang t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]356 t.c:4:8: <span class="err">error:</span> expected ';' after expression
357 <span class="snip"> bar()</span>
358 <span class="point"> ^</span>
359 <span class="point"> ;</span>
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]360</pre>
361
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]362<p>The following example shows much better error recovery than GCC. The message coming out
363of GCC is completely useless for diagnosing the problem. Clang tries much harder
364and produces a much more useful diagnosis of the problem.</p>
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]365
366<pre>
367 $ <b>gcc-4.2 t.c</b>
368 t.c:3: error: expected '=', ',', ';', 'asm' or '__attribute__' before '*' token
369 $ <b>clang t.c</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]370 t.c:3:1: <span class="err">error:</span> unknown type name 'foo_t'
371 <span class="snip">foo_t *P = 0;</span>
372 <span class="point">^</span>
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]373</pre>
374
Douglas Gregord89df5a2011-06-01 22:45:49 +0000[diff] [blame]375<p>The following example shows that we recover from the simple case of
376forgetting a ; after a struct definition much better than GCC.</p>
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]377
Chris Lattner94634cc2010-02-02 01:35:23 +0000[diff] [blame]378<pre>
379 $ <b>cat t.cc</b>
380 template&lt;class T&gt;
381 class a {}
382 class temp {};
383 a&lt;temp&gt; b;
384 struct b {
385 }
386 $ <b>gcc-4.2 t.cc</b>
387 t.cc:3: error: multiple types in one declaration
388 t.cc:4: error: non-template type 'a' used as a template
389 t.cc:4: error: invalid type in declaration before ';' token
390 t.cc:6: error: expected unqualified-id at end of input
391 $ <b>clang t.cc</b>
Benjamin Kramer665a8dc2012-01-15 15:26:07 +0000[diff] [blame]392 t.cc:2:11: <span class="err">error:</span> expected ';' after class
393 <span class="snip">class a {}</span>
394 <span class="point"> ^</span>
395 <span class="point"> ;</span>
396 t.cc:6:2: <span class="err">error:</span> expected ';' after struct
397 <span class="snip">}</span>
398 <span class="point"> ^</span>
399 <span class="point"> ;</span>
Chris Lattner94634cc2010-02-02 01:35:23 +0000[diff] [blame]400</pre>
401
Chris Lattner0e3b44b2009-09-30 20:19:10 +0000[diff] [blame]402<p>While each of these details is minor, we feel that they all add up to provide
403a much more polished experience.</p>
404
Chris Lattner76766012009-03-19 18:52:17 +0000[diff] [blame]405</div>
406</body>
407</html>