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| <h2 class="chapter">5 Diagnostics</h2> |
| |
| <p><a name="index-diagnostic-93"></a><a name="index-reporting-errors-94"></a><a name="index-reporting-warnings-95"></a> |
| <a name="index-g_t_0023error-96"></a>The directive ‘<samp><span class="samp">#error</span></samp>’ causes the preprocessor to report a fatal |
| error. The tokens forming the rest of the line following ‘<samp><span class="samp">#error</span></samp>’ |
| are used as the error message. |
| |
| <p>You would use ‘<samp><span class="samp">#error</span></samp>’ inside of a conditional that detects a |
| combination of parameters which you know the program does not properly |
| support. For example, if you know that the program will not run |
| properly on a VAX, you might write |
| |
| <pre class="smallexample"> #ifdef __vax__ |
| #error "Won't work on VAXen. See comments at get_last_object." |
| #endif |
| </pre> |
| <p>If you have several configuration parameters that must be set up by |
| the installation in a consistent way, you can use conditionals to detect |
| an inconsistency and report it with ‘<samp><span class="samp">#error</span></samp>’. For example, |
| |
| <pre class="smallexample"> #if !defined(UNALIGNED_INT_ASM_OP) && defined(DWARF2_DEBUGGING_INFO) |
| #error "DWARF2_DEBUGGING_INFO requires UNALIGNED_INT_ASM_OP." |
| #endif |
| </pre> |
| <p><a name="index-g_t_0023warning-97"></a>The directive ‘<samp><span class="samp">#warning</span></samp>’ is like ‘<samp><span class="samp">#error</span></samp>’, but causes the |
| preprocessor to issue a warning and continue preprocessing. The tokens |
| following ‘<samp><span class="samp">#warning</span></samp>’ are used as the warning message. |
| |
| <p>You might use ‘<samp><span class="samp">#warning</span></samp>’ in obsolete header files, with a message |
| directing the user to the header file which should be used instead. |
| |
| <p>Neither ‘<samp><span class="samp">#error</span></samp>’ nor ‘<samp><span class="samp">#warning</span></samp>’ macro-expands its argument. |
| Internal whitespace sequences are each replaced with a single space. |
| The line must consist of complete tokens. It is wisest to make the |
| argument of these directives be a single string constant; this avoids |
| problems with apostrophes and the like. |
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