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| <h3 class="section">12.1 Have You Found a Bug?</h3> |
| |
| <p><a name="index-bug-criteria-3257"></a> |
| If you are not sure whether you have found a bug, here are some guidelines: |
| |
| |
| <a name="index-fatal-signal-3258"></a> |
| <a name="index-core-dump-3259"></a> |
| <ul><li>If the compiler gets a fatal signal, for any input whatever, that is a |
| compiler bug. Reliable compilers never crash. |
| |
| <p><a name="index-invalid-assembly-code-3260"></a><a name="index-assembly-code_002c-invalid-3261"></a><li>If the compiler produces invalid assembly code, for any input whatever |
| (except an <code>asm</code> statement), that is a compiler bug, unless the |
| compiler reports errors (not just warnings) which would ordinarily |
| prevent the assembler from being run. |
| |
| <p><a name="index-undefined-behavior-3262"></a><a name="index-undefined-function-value-3263"></a><a name="index-increment-operators-3264"></a><li>If the compiler produces valid assembly code that does not correctly |
| execute the input source code, that is a compiler bug. |
| |
| <p>However, you must double-check to make sure, because you may have a |
| program whose behavior is undefined, which happened by chance to give |
| the desired results with another C or C++ compiler. |
| |
| <p>For example, in many nonoptimizing compilers, you can write ‘<samp><span class="samp">x;</span></samp>’ |
| at the end of a function instead of ‘<samp><span class="samp">return x;</span></samp>’, with the same |
| results. But the value of the function is undefined if <code>return</code> |
| is omitted; it is not a bug when GCC produces different results. |
| |
| <p>Problems often result from expressions with two increment operators, |
| as in <code>f (*p++, *p++)</code>. Your previous compiler might have |
| interpreted that expression the way you intended; GCC might |
| interpret it another way. Neither compiler is wrong. The bug is |
| in your code. |
| |
| <p>After you have localized the error to a single source line, it should |
| be easy to check for these things. If your program is correct and |
| well defined, you have found a compiler bug. |
| |
| <li>If the compiler produces an error message for valid input, that is a |
| compiler bug. |
| |
| <p><a name="index-invalid-input-3265"></a><li>If the compiler does not produce an error message for invalid input, |
| that is a compiler bug. However, you should note that your idea of |
| “invalid input” might be someone else's idea of “an extension” or |
| “support for traditional practice”. |
| |
| <li>If you are an experienced user of one of the languages GCC supports, your |
| suggestions for improvement of GCC are welcome in any case. |
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