Re: Function pointer casting

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#820

From: Edward Chew
Date: Mon, 02 Jun 2003 15:20

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MW Ron wrote:
> In article <3ED6734A.6080600@lgl.kos.net>,
>  Edward Chew <ekc-noreply@lgl.kos.net> wrote:
> 
> 
>>After upgrading to CW 8, I notice the compiler no longer allows implicit 
>>casting from function pointers (e.g. "int (*)()") to void*.  Is this a 
>>bug or some weird C/C++ standards compliance thing?  For now, it seems 
>>happy if I write static_cast<void*>(fn).
> 
> 
> This is not legal implicitly or explicitly but we allow the explicit 
> cast because this is common for legacy code.  

Interesting.  I wonder why it would be illegal, and what the legal 
alternative would be?  I ran into this problem when weak-linking to 
certain CFM libraries and testing to see if they are available.  In 
Apple literature, they recommend testing the init routine like this:

     if(LibraryInitFunction == kUnresolvedCFragSymbolAddress)
         reportLibraryUnavailable();

This will immediately cause a type mismatch error at compile time in 
Codewarrior 8.  Figuring a pointer is a pointer, I rewrote this as:

     if(static_cast<void*>(LibraryInitFunction) ==
        static_cast<void*>(kUnresolvedCFragSymbolAddress)
        )
          reportLibraryUnavailable();

This seems to work fine, but now I am told it is illegal as well.  What 
would be the proper test in that case?

Edward K. Chew

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References: <3ED6734A.6080600@lgl.kos.net> <mwron-5286CB.09413702062003@enews.newsguy.com>

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Date: Mon, 02 Jun 2003 11:20:00 -0400
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