[Freeciv-Dev] Re: (PR#2461) bool type already exists

["Raimar Falke via RT" <rt@xxxxxxxxxxxxxx>]

On Sun, Dec 01, 2002 at 11:04:44AM -0800, Raimar Falke via RT wrote:
>        7.1.7  Boolean type and values <stdbool.h>
> 
>        [#1] The header  <stdbool.h>  defines  one  type  and  three
>        macros.
> 
>        [#2] The type is
> 
>                bool
> 
>        which is an integer type that promotes to  int  or  unsigned
>        int,  and  that is suitable to be used as the type of a bit-
>        field.  A bit-field of any width  and  type  bool  shall  be
>        capable for representing the value 1.138
> 
> 
>        __________
> 
>        138. The  traditional choice for type bool has been int, but
>            this  is  not  a  requirement  of   this   International
>            Standard.   Other available choices include, but are not
>            limited to, char, unsigned int, and an enumeration type.
> 
>            If an enumeration type is chosen, the names of its  true
>            and  false  members  are "masked" by the macros true and
>            false, but the member names might be  available  to  the
>            debugger:
> 
>            typedef enum { false=0, true=1 } bool;
>            #define false 0
>            #define true 1
> 
>            The type is  suitable  for  bit-fields  if  it  is  int,
>            unsigned  int,  signed  int,  or some type allowed by an
> 
>        [#3] The macros are
> 
>                true
> 
>        which expands to the decimal constant 1,
> 
>                false
> 
>        which expands to the decimal constant 0, and
> 
>                __bool_true_false_are_defined
> 
>        which expands to the decimal constant  1.   The  macros  are
>        suitable for use in #if preprocessing directives.

In addition to the above (I only had a working draft from 97 and now I
have one from 98 but still not the final one) it looks like the final
C99 also contains the following:

       [#2] An object declared as type _Bool  is  large  enough  to
       store the values 0 and 1.
...
       6.3.1.2  Boolean type

       [#1] When any scalar value is converted to _Bool, the result
       is 0 if the value compares equal to 0; otherwise, the result
       is 1.

This basically means that the bool type (_Bool) is a first level type
(it is for example a reserved keyword like for example "char", "auto",
"inline" or "if").

The second point above means that if you run this code:

#include <stdio.h>

int main()
{
  _Bool a, b = 23;
  int i = 45;

  a = i;

  printf("%d %d %d\n", b, i, a);
  return 0;
}

You get 
1 45 1
and not
23 45 45
which you would get if you use a simple typedef.

We shouldn't rely on this behavior (this isn't hard).

        Raimar

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