Re: integer and floating-point bit pattern

From: Jack Klein (jackklein_at_spamcop.net)
Date: 10/02/03 

Date: Thu, 02 Oct 2003 03:38:42 GMT

On 1 Oct 2003 13:56:10 -0700, nethlek@tokyo.com (Mantorok Redgormor)
wrote in comp.lang.c:

> Would the following determine if the bit pattern for
> floating point 0.0 and integer 0 are the same?
>
> #include <stdio.h>
> int main(void)
> <%
> if(0 == 0.0f)
> puts("Bit pattern is the same.");
>
> return 0;
> %>
>
>
> Also is it undefined behavior for failure
> to include the proper header file for any
> function or just functions that accept a
> variable number of arguments?

Mike already answered your first question, he was a little unsure
about the second.

It is not and has never been a requirement in C that you include
header files, except in a few cases where data types with
implementation-defined types and members (such as time_t, FILE, etc.).

Prior to the current (1999) standard you did not need a prototype or a
declaration to call a function that returned int and accepted a fixed
number and type of arguments, if all the argument types were those
provided by default promotions.

Under the current standard, there must be at least a declaration in
scope for any function you call, specifying the return type. Implicit
int is illegal, including the return type of functions. The
declaration does not need to be a prototype if the function accepts a
fixed number and type of arguments if the types are the default
promotions.

Since the very first 1989 ANSI standard, it produces undefined
behavior to call a variadic function without a full prototype in
scope.

It is perfectly valid under all versions of the C standard to provide
your own prototype for a standard function so long as you get it
correct.

If you write a prototype equivalent to:

   char *strchr(const char *s, int c);

...then you can call this function without including <string.h>. 

-- 
Jack Klein
Home: http://JK-Technology.Com
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