Where is stdbool.h?

Question

I want to find the _Bool definition on my system, so for systems where it\'s missing I can implement it. I\'ve seen various definitions for it here and on other

Answer 1

some compilers don't offer _Bool keywords, so I wrote my own stdbool.h :

#ifndef STDBOOL_H_
#define STDBOOL_H_

/**
 * stdbool.h
 * Author    - Yaping Xin
 * E-mail    - xinyp at live dot com
 * Date      - February 10, 2014
 * Copyright - You are free to use for any purpose except illegal acts
 * Warrenty  - None: don't blame me if it breaks something
 *
 * In ISO C99, stdbool.h is a standard header and _Bool is a keyword, but
 * some compilers don't offer these yet. This header file is an 
 * implementation of the stdbool.h header file.
 *
 */

#ifndef _Bool
typedef unsigned char _Bool;
#endif /* _Bool */

/**
 * Define the Boolean macros only if they are not already defined.
 */
#ifndef __bool_true_false_are_defined
#define bool _Bool
#define false 0 
#define true 1
#define __bool_true_false_are_defined 1
#endif /* __bool_true_false_are_defined */

#endif /* STDBOOL_H_ */

Answer 2

Other people have replied to the question on _Bool location and finding if C99 is declared... however, I am not satisfied with the self-made declaration everyone gave.

Why won't you completely define the type?

typedef enum { false, true } bool;

Answer 3

_Bool is a predefined type in C99, much like int or double. You will not find the definition for int in any header file either.

What you can do is

• check the compiler is C99
• if it is use _Bool
• otherwise use some other type (int or unsigned char)

For example:

#if defined __STDC__ && defined __STDC_VERSION__ && __STDC_VERSION__ >= 199901L
/* have a C99 compiler */
typedef _Bool boolean;
#else
/* do not have a C99 compiler */
typedef unsigned char boolean;
#endif

Answer 4

_Bool is a built-in type, so don't expect to find a definition for it in a header file, even a system header file.

Having said that, guessing your system from the paths that you are searching, have you looked in /usr/lib/gcc/*/*/include ?

My "real" stdbool.h lives there. As expected it #defines bool to be _Bool. As _Bool is a type native to the compiler there's no definition for it in the header file.

Answer 5

$ echo '_Bool a;' | gcc -c -x c -
$ echo $?
0

$ echo 'bool a;' | gcc -x c -c -
<stdin>:1: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘a’

This demonstrates that _Bool is a built-in type and bool is not, by compiling a single variable declaration with no includes.

Answer 6

As a note:

The _Bool is defined in C99. If you build your program with:

gcc -std=c99

You can expect it to be there.