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WittyGuy
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 Posted: Thu Jul 27, 2006 9:10 am Post subject: typecasting function pointer to void* |
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How to typecast a "function pointer" to "const void*" type in C++ way?
int MyFunction (double money); // Function prototype
const void* arg = (const void*)MyFunction; // type casting function
pointer to const void* in C-style
void(*pFunc)() = (void(*)())(arg); // type casting const void* to function
pointer in C-style
(*pFunc)(); // Calling the function after type casting is done
Is typecasting like above is safe anyway?
regards,
Sukumar |
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Florian Stinglmayr
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| Posted: Thu Jul 27, 2006 9:10 am Post subject: Re: typecasting function pointer to void* |
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WittyGuy schrieb:
| Quote: | How to typecast a "function pointer" to "const void*" type in C++ way?
int MyFunction (double money); // Function prototype
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I suggest you to create a typedef for the function pointer:
typedef int (*TMyFunction) ( double );
And then use it!
void * ptr = static_cast<void*>(&some_func);
....
(static_cast<TMyFunction>(ptr))(23.42): |
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Kai-Uwe Bux
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| Posted: Thu Jul 27, 2006 9:11 am Post subject: Re: typecasting function pointer to void* |
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WittyGuy wrote:
| Quote: | How to typecast a "function pointer" to "const void*" type in C++ way?
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There is no "how".
| Quote: | int MyFunction (double money); // Function prototype
const void* arg = (const void*)MyFunction; // type casting function
pointer to const void* in C-style
void(*pFunc)() = (void(*)())(arg); // type casting const void* to function
pointer in C-style
(*pFunc)(); // Calling the function after type casting is done
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You are casting back to a different signature. Even if there was a roundtrip
guarantee through void* (which there is not), this conversion would be
unspecified.
| Quote: | Is typecasting like above is safe anyway?
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No: In C++ there is no round-trip guarantee for pointer-to-function or
pointer-to-member-function to void* and back. Just don't do it.
Function pointers are convertible to a different signature, however, the
result of such conversion cannot be used: it can only be converted back.
However, this does allow you to use void(*)(void) as a universal function
pointer to and from which you can cast (reinterpret_cast is the one you
might want to use) [5.2.10/6].
Best
Kai-Uwe Bux |
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