Author: Gerd Isenberg
Date: 07:58:06 09/26/03
Go up one level in this thread
On September 26, 2003 at 07:51:49, Russell Reagan wrote:
>On September 26, 2003 at 06:50:59, Gerd Isenberg wrote:
>
>>This own BOOL type is of course not "typesafe" as bool, as you may assign any
>>"int" expressions to it. With BOOL one should interprete zero as FALSE and any
>>other value as TRUE. Due to this ambiguity, comparing BOOL-expressions with TRUE
>>may be erroneous, so better compare with != FALSE.
>
>Hi Gerd,
>
>I've seen people do it like this:
>
>typedef int BOOL;
>
>#define FALSE (0)
>#define TRUE (!FALSE)
Hi Russell,
Yes, see ms WINDEF.H
typedef int BOOL;
#ifndef FALSE
#define FALSE 0
#endif
#ifndef TRUE
#define TRUE 1
#endif
>
>I have also heard that if you use C++ 'bool', that sometimes the compiler can
>make some optimizations since it knows it will always be a zero or one. With a
>'BOOL', I'm not sure if it will know that. I guess you could try this:
>
>enum BOOL { FALSE, TRUE };
>
>Then the compiler might assume that a 'BOOL' is always zero or one, and you
>couldn't assign other values to a 'BOOL'.
>
Yes, that seems safe, but has some other drawbacks:
BOOL cond = (a > b); // is an error and has to use an explicite cast
BOOL cond = (BOO)(a > b):
BOOL cond = (a > b) ? TRUE : FALSE; // or conditional assignment
Even if it produces the same branchless code, i found that annoying.
>I don't think that the sizeof(bool) is always 1. I think it is 4 on some
>compilers. When BOOL is an enum, the sizeof(BOOL) is 4 in MSVC.
>
>
>#include <iostream>
>
>enum BOOL { FALSE, TRUE };
>
>int main ()
>{
> std::cout << "sizeof(bool) is " << sizeof(bool) << std::endl;
> std::cout << "sizeof(BOOL) is " << sizeof(BOOL) << std::endl;
> return 0;
>}
>
>sizeof(bool) is 1
>sizeof(BOOL) is 4
I see, thanks.
The problem arises with ms .net and language independent data types.
Gerd
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