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How do I inhibit "note C6311" in Microsoft C compiler?

Answer 1

+6 A:

You are not allowed to redefine a macro unless the new definition is identical to the current definition (if you redefine a macro and the new definition is different than the current definition, the program is actually ill-formed).

#undefing the macro before redefining it is the correct thing to do in this case:

#undef FOOBAR
#define FOOBAR FOO


#undef FOOBAR
#define FOOBAR BAR

Note that you are allowed to use #undef even if a macro name isn't currently defined, so there's no reason to test whether the macro is defined using #ifdef before using #undef on it.

James McNellis 2010-04-20 16:25:59

I know from N1124, 6.10.3 / 2 says exactly that. Since the C compiler only issues a warning which can be inhibited, I was hoping there was another method to inhibit the following note.

piCookie 2010-04-20 16:33:22

@piCookie: Why would you want to suppress this warning? The compiler is telling you that you code is _wrong_. The code should be fixed, especially since the fix is really easy.

James McNellis 2010-04-20 16:36:30

Maybe he doesn't know about `#ifdef`

Johannes Schaub - litb 2010-04-20 16:40:37

@Johannes: You are allowed to `#undef` a macro name even if the macro isn't defined, but _that_ might not be common knowledge. I've added an example demonstrating that; thanks.

James McNellis 2010-04-20 16:44:42

@James, ah haven't known. Thanks for enlighting me.

Johannes Schaub - litb 2010-04-20 16:53:08

@Johannes: I must not use #ifdef because I actually need each definition in order. @James: As to why I would want to suppress it; I had already implemented the correct fix with #undef before posting the question. However, since the compiler does not treat this as an error condition, but an ignorable warning instead, I wanted to use the compiler to suppress the note as well. I have examined the code and know that each definition in order is what I want. I would like to know if it is possible also to suppress the note. Perhaps more generally, is it possible to suppress notes?

piCookie 2010-04-20 23:18:20

@piCookie: I don't know how to suppress notes if you can't do it with `#pragma warning(disable:...)`, however, upgrading to a more recent version of Visual C++ would solve your problem. Visual C++ 2010 does not emit this note you are seeing. I no longer have older versions installed on this PC, but I can check 2003/2005/2008 at work tomorrow.

James McNellis 2010-04-23 01:03:16

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How do I inhibit "note C6311" in Microsoft C compiler?

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