Thread: "bool" in C

Hi,
I have (unfortunately) found out that C doesn't support the "bool" keyword. So what is the most common (or best) way to use boolean statements in my code?
I have tried this:

Code:

typedef int bool;

and then I used "0" instead of "false" and "1" instead of "true".

But this seems to me a little "waste" of memory. I just want to store only 2 values (true and false) but I use "4 bytes" (sizeof(int)) instead. So maybe it would be better to use this:

Code:

typedef char bool;

and occupy only "1 byte" (sizeof(char)) of memory. But what should then I use instead of "false" and "true"? For example 'n' and 'y', or what?

Thanks.

If you are compiling in C99, you could #include <stdbool.h> and use bool, true, and false. bool would be a macro for _Bool, which itself is a standard type guaranteed to hold 0 or 1, and true and false are macros for 1 and 0 respectively.

If not, you could just use 0 and 1 directly. I would not be too concerned about wasting memory, unless it really is a problem.

Just use 0 & 1.

Originally Posted by laserlight

If you are compiling in C99, ...

Just a little question. What is "C99"? I have seen that also in some other posts here, but I have never seen it before? It is some type of compiler?
By the way, I use "Microsoft Visual Studio 2008".

Originally Posted by Petike

What is "C99"?

The 1999 edition of the C Standard.

It usually exists on most compilers, even C89 ones. So if it exists use it, otherwise define your own macros.

The compiler may even optimize (I haven't checked), so don't worry about the memory.

Visual Studio does not have support for the 1999 C standard, though.
Also, a char can hold 0 and 1, since it is basically an integral (characters are actually translated into integers).

Originally Posted by sergioms

Code:

#if (__BORLANDC__ <= 0x460) || !defined(__cplusplus)	// Define o Tipo Booleano para o C
  typedef enum { false, true } bool;
#endif

That's a fairly specific implementation, but yes, that sort of thing will work.

--
Mats

Originally Posted by sergioms

Code:

#if (__BORLANDC__ <= 0x460) || !defined(__cplusplus)	// Define o Tipo Booleano para o C
  typedef enum { false, true } bool;
#endif

stdbool.h is guaranteed to work in macros. You've just broken that gaureentee.

Originally Posted by C_ntua

You can also define true and false

Code:

#define true 1
#define false 0
typedef char bool;

and use it normaly, like bool h = false (with the obvious risks of using #define)

Except they might already be defined, so undefine them first :-). Using the man page as a reference...

Code:

#ifdef __bool_true_false_are_defined
#   undef true
#   undef false
#   undef bool

#   define true 1
#   define false 0
#   define bool char
#endif

Don't worry about wasting space (if you still are use unsigned short int which "wastes" as much space as a char). I agree w/ cpjust, use 0 = FALSE and non-zero = TRUE (where non-zero would probably be 1) and just check for > 0. Not that hard, also no point having a type that can only hold 0 or 1 when you use it proparly.

Macros cannot contain spaces, but you can easily append _ before or after.

But what if I wanted, "is_true_and_stuff" :-)

Y'arrh the pre-processor be a harsh mistress.