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1 | <html> |
2 | <head> | |
3 | <title>BOOST_PP_LINE</title> | |
4 | <link rel="stylesheet" type="text/css" href="../styles.css"> | |
5 | </head> | |
6 | <body> | |
7 | <div style="margin-left: 0px;"> | |
8 | The <b>BOOST_PP_LINE</b> macro places notes encoded as line directives in the preprocessing output. | |
9 | </div> | |
10 | <h4>Usage</h4> | |
11 | <div class="code"> | |
12 | #line <b>BOOST_PP_LINE</b>(<i>line</i>, <i>file</i>) | |
13 | </div> | |
14 | <h4>Arguments</h4> | |
15 | <dl> | |
16 | <dt>line</dt> | |
17 | <dd> | |
18 | The new line number of the trailing line. | |
19 | The predefined macro <i>__LINE__</i> is commonly used. | |
20 | </dd> | |
21 | <dt>file</dt> | |
22 | <dd> | |
23 | Typically the name of the current file. | |
24 | However, any informative text will work. | |
25 | This text is internally stringized, so quotation marks are unnecessary. | |
26 | </dd> | |
27 | </dl> | |
28 | <h4>Remarks</h4> | |
29 | <div> | |
30 | If the macro <b>BOOST_PP_CONFIG_EXTENDED_LINE_INFO</b> is defined as <i>1</i> and a <i>file-iteration</i> | |
31 | is in progress, this macro will automatically insert debugging information about the state of <i>file-iteration</i>. | |
32 | This information will show the all of the current iteration values with the inner most iteration last. | |
33 | </div> | |
34 | <div> | |
35 | This information is useful when errors might be spanning multiple iterations of the same source text. | |
36 | Finding any errors is sometimes less than straightforward. | |
37 | Use of this macro can provide information to make this much easier. | |
38 | For example, instead of getting several errors like this: | |
39 | <div><i> | |
40 | "file.hpp", line 2: error: expected a ";"<br> | |
41 | "file.hpp", line 4: error: improperly terminated macro invocation<br> | |
42 | </i></div> | |
43 | You might get something like this instead.... | |
44 | <i><div> | |
45 | "file.hpp [1]", line 2: error: expected a ";"<br> | |
46 | "file.hpp [5]", line 4: error: improperly terminated macro invocation<br> | |
47 | </i></div> | |
48 | It is immediately evident that this error is spanning multiple iterations of the same source text. | |
49 | If it wasn't, the same errors would occur on each iteration. | |
50 | </div> | |
51 | <div> | |
52 | It must be noted however, that some compilers don't like filenames that aren't actually files. | |
53 | Those compilers typically issues warnings about the bad filename. | |
54 | This makes it a good idea to only define <b>BOOST_PP_CONFIG_EXTENDED_LINE_INFO</b> to <i>1</i> <i>only</i> when debugging. | |
55 | </div> | |
56 | <h4>See Also</h4> | |
57 | <ul> | |
58 | <li><a href="config_extended_line_info.html">BOOST_PP_CONFIG_EXTENDED_LINE_INFO</a></li> | |
59 | </ul> | |
60 | <h4>Requirements</h4> | |
61 | <div> | |
62 | <b>Header:</b> <a href="../headers/debug/line.html"><boost/preprocessor/debug/line.hpp></a> | |
63 | </div> | |
64 | <h4>Sample Code</h4> | |
65 | <div><pre> | |
66 | // sample.cpp | |
67 | #if !defined(<a href="is_iterating.html">BOOST_PP_IS_ITERATING</a>) | |
68 | ||
69 | #define <a href="config_extended_line_info.html">BOOST_PP_CONFIG_EXTENDED_LINE_INFO</a> 1 | |
70 | ||
71 | #include <<a href="../headers/arithmetic/dec.html">boost/preprocessor/arithmetic/dec.hpp</a>> | |
72 | #include <<a href="../headers/cat.html">boost/preprocessor/cat.hpp</a>> | |
73 | #include <<a href="../headers/debug/line.html">boost/preprocessor/debug/line.hpp</a>> | |
74 | #include <<a href="../headers/iteration/iterate.html">boost/preprocessor/iteration/iterate.hpp</a>> | |
75 | ||
76 | namespace sample { | |
77 | ||
78 | #define <a href="iteration_params_x.html">BOOST_PP_ITERATION_PARAMS_1</a> (3, (1, 5, "sample.cpp")) | |
79 | #include <a href="iterate.html">BOOST_PP_ITERATE</a>() | |
80 | ||
81 | } // sample | |
82 | ||
83 | int main(void) { | |
84 | return 0; | |
85 | } | |
86 | ||
87 | #else | |
88 | ||
89 | #line <a href="line.html">BOOST_PP_LINE</a>(1, sample.cpp) | |
90 | ||
91 | int <a href="cat.html">BOOST_PP_CAT</a>(x, <a href="iteration.html">BOOST_PP_ITERATION</a>())); // extra parenthesis | |
92 | ||
93 | struct <a href="cat.html">BOOST_PP_CAT</a>(s, <a href="dec.html">BOOST_PP_DEC</a>(<a href="iteration.html">BOOST_PP_ITERATION</a>()) { | |
94 | // missing a parenthesis | |
95 | // ... | |
96 | }; | |
97 | ||
98 | #endif | |
99 | </pre></div> | |
100 | <hr size="1"> | |
101 | <div style="margin-left: 0px;"> | |
102 |