Fixed bool type for C89

[damon-kwok]

Before c99 doesn't have _Bool‘ and STDC_VERSION'. Compensate.

#ifndef __STDC_VERSION__
#define __STDC_VERSION__ 0
#endif
#if defined(_MSC_VER) || (__STDC_VERSION__ < 199901L)
/* `MSVC' and `Before c99' doesn't have <stdbool.h>. Compensate. */
typedef char bool;
#define true (bool) 1
#define false (bool) 0
#else
#include <stdbool.h>
#endif

[grynspan]

What compilation environment are you using where you are constrained to C89? :)

[grynspan]

MSVC++ definitely has stdbool.h, and defining bool in this way will conflict with the standard library's definition there.

If this is a real target you're trying to support, then presumably it's an old version of MSVC++? If so, you might just want to check for the existence of the header instead:

#if __has_include(<stdbool.h>)
#include <stdbool.h>
#else
typedef char bool;
#define true ((bool)1)
#define false ((bool)0)
#endif

Note how I've wrapped the (bool) 1 in parentheses: this is necessary in a macro definition in certain lexical contexts where (bool) 1 could instead be parsed as e.g. f(bool) 1 and which would produce an ill-formed program or unexpected behaviour.

Alternatively, if for some reason you can't use __has_include, you can check for an old version of C like so:

#if !defined(__cplusplus) && (!defined(__STDC_VERSION__) || __STDC_VERSION__ < 199901L)

But again, if you're trying to port your code to some old version of MSVC++, a bit of explanation might be in order. :)