Re: main function address

From: Martin Dickopp (expires-2004-05-31_at_zero-based.org)
Date: 04/07/04 

Date: Wed, 07 Apr 2004 20:26:00 +0200

pete <pfiland@mindspring.com> writes:

> Lew Pitcher wrote:
>>
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>> pete wrote:
>> | Martin Dickopp wrote:
>> |
>> |>Lew Pitcher <lpitcher@sympatico.ca> writes:
>> |>
>> |>
>> |>>#include <stdio.h>
>> |>>#include <stdlib.h>
>> |>>
>> |>>int main(void)
>> |>>{
>> |>> printf("main() at %p\n",(void *)&main);
>> |>>
>> |>> return EXIT_SUCCESS;
>> |>>}
>> |>
>> |>Is the cast to `void *' valid?
>> |
>> |
>> | No.
>> |
>> | In N869, it's one of the common extensions.
>> |
>> | J.5.7 Function pointer casts
>> | [#2] A pointer to a function may be cast to a pointer to an
>> | object or to void, allowing a function to be inspected or
>> | modified (for example, by a debugger) (6.5.4).
>> |
>> | ... which makes it more obviously not part of standard C.
>>
>> In 9989-1999 (admittedly, just the draft C99 standard, and not the
>> /actual standard itself), the printf() function documentation in
>> 7.19.6.3 refers the reader to the fprintf() documentation for a
>> description of it's input. The fprintf() documentation in 7.19.6.1 says
>> of the %p format
>>
>> ~ p The argument shall be a pointer to void. The value of the pointer is
>> ~ converted to a sequence of printing characters, in an
>> ~ implementation-defined manner.
>>
>> So, to satisfy the %p format character, the argument to
>> fprintf()/printf() /must/ be a "pointer to void". Since main is a
>> "pointer to function returning int", and not a "pointer to void", I
>> interpreted the documentation as requiring a cast to void pointer.
>
> I interpret it as meaning that printing the address of a function
> isn't something that you are guaranteed to be able to do.

So do I. You certainly cannot do it with the `%p' specifier. 6.3.2.3#1
makes it quite clear that only pointers to incomplete or object type can
be converted to `void *'.

Martin 

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