How to define the boolean in C

[vnrabbit]

Hi All,

I want to define a variable by type boolean in C and I don't know how. Is there anyone know, please help me? Thanks a lot!

[Shiro]

You could us an enummeration for that.

typedef
{
    FALSE,
    TRUE
} boolean;

Or, if your compiler supports the latest C-standard (C99), you can include stdbool.h and use the bool-type.

[vnrabbit]

Thanks Shiro.
I wonder when you coded like that, TRUE = 1 and FALSE = 0, right?

typedef
{
    FALSE,
    TRUE
} boolean;

struct dataInfo {
   boolean DataReady;
}

 So in later in program, I put the check statement 

if (DataReady)
  { .... doing someting;
     DataReady = FALSE;
   }

Is this OK?

[Shiro]

Yes, FALSE == 0.

Hmmm, I made a mistake. Sorry, it should be:

typedef enum
{
  FALSE,
  TRUE
} boolean;

>if (DataReady)

That is OK, if this DataReady is a standalone variable and not a member of dataInfo.

[vnrabbit]

=> That is OK, if this DataReady is a standalone variable and not a member of dataInfo

What do you mean by saying that? Sorry for slow understanding.

[Shiro]

I referred to this:

> struct dataInfo {
> boolean DataReady;
> }

Take a look at this:

/* A variable of type struct dataInfo, containing DataReady. */
struct dataInfo dataInfo_variable;

/* A "stand-alone" DataReady variable. */
boolean DataReady;

/* Use DataReady as stored in the structure-variable. */
if (dataInfo_variable.DataReady == FALSE)
{
}

/* Use the "stand-alone" DataReady variable. */
if (DataReady == FALSE)
{
}

Probably "stand-alone" is not the correct word, but I don't know the correct English word for it.

[vnrabbit]

I got it. Thanks a bunch.

[pinko_liberal]

Originally posted by Shiro

Probably "stand-alone" is not the correct word, but I don't know the correct English word for it.

From the standard :

The type char, the signed and unsigned integer types, and the enumerated types are collectively called integer types. The integer and real floating types are collectively called real types.

A real type might be the proper expression here.

[whistlenm1]

just an idea:
typedef enum boolean { False, True} bool_t;

[Mister C]

Why not

#define TRUE 1
#define FALSE 0

Isn't this the simplest?

Also, C99 does support boolean type. Use it if you can.

[Prelude]

>Isn't this the simplest?
It depends on your point of view. I personally prefer a specialized type defined as boolean (for C89) to aid in readability:

typedef enum { BFALSE, BTRUE } bool_t;

Now instead of int you declare a bool_t, I consider this to be more readable. Your mileage may vary.

-Prelude

[Vber]

I'll go with the same way as Mr.C:

#define TRUE 1
#define FALSE 0

This isn't the most elegant, but it works
In your program you can do this:

bLegalVal = FALSE;

But this isn't a new type, to use the bool type, define him with typedef as people told you here.

[Shiro]

>This isn't the most elegant, but it works

Using a defined type also works, in fact it works almost the same way, but it is more readable. The constant values in the enum can be used just like the #define'd values. Look at this:

int a;
boolean b;

From variable b it is immediately clear that it is a boolean-variable, it is not clear from variable a. In my opinion it is good to make a program elegant and readable.

[Vber]

Ohh, I see now shiro, it really looks strange something like that:

int bCorr = FALSE

It's really more readable:

boolean bCorr = FALSE

I didn't think about it