C99 's new keyword _bool__c language

The C99 standard defines a new keyword _bool that provides a Boolean type. Previously, C programmers always used their own methods to define Boolean types.

0 is false, and not 0 is true.

You might use the char type to represent a Boolean type, or you might use an int type to represent a Boolean type.

Many function libraries define their own Boolean types and corresponding macros, enumerations, and typedef.

Now C99 has brought in the native Boolean type of C language.

#include<stdbool.h>

This header file defines a macro such as Bool,true,false.

#ifndef__cplusplus

If it is not C + +, it is pure C, then defining the macro bool is equivalent to the _bool type.

#definebool_bool

#defineTrue 1

#defineFalse 0

#else/* __cplusplus * *

If it is C + +, then the _bool type is defined as bool type.

/*supporting <stdbool.h> in C + + is a GCC extension. */

#define _bool Bool

#defineBOOL

#defineFalse

#defineTrue

#endif/* __cplusplus * *

/*signal that all the definitions are present. * *

#define__bool_true_false_are_defined 1

See if the above macro is ==1, and if so, it means the above definitions are available.

The draft C2008 said:

AnObject declared as Type_boolis large enough to store the values 0 and1.

That is, only the size of the _bool type is specified to hold at least 0 and 1 of the two values. Does not specify the specific size. This is given to the compiler to play it free.

I did a test with GCC:

printf ("sizeof (BOOL):%d\n",sizeof(bool));

printf ("sizeof (char):%d\n",sizeof(char));

printf ("sizeof (int):%d\n",sizeof(int));

printf ("sizeof (long):%d\n",sizeof(long));

--sizeof (BOOL): 1

--sizeof (char): 1

--sizeof (int): 4

--sizeof (Long): 8

It seems that GCC uses char to implement the _bool type.

See what happens when you assign a value to a _bool type:

boolboolean=-11212112;

printf ("boolean:%d\n", Boolean);

--boolean:1

It appears that the GCC compiler treats the _bool type with its own conversion process. If 0 is assigned to the _bool type, then a value of 0 is assigned. If it is any other data, it will be assigned a value of 1. (Just don't know if other compilers are doing this, the C2008 standard draft does not elaborate on this part)

Used all the time. Logical non-operator:

if (!flag) {

}

To represent 0 and not 0. Now the _bool type is only 0 and 1.