Why was the boolean data type not implemented in C

Question

One of my friends asked a question, why is there no Boolean data type in the C programming language. I did a bit of searching and reading. I got few questions and answers in stack overflow saying that,

All data types should be addressable, and a bit cannot be addressed.
The basic data structure at the hardware level of mainstream CPUs is a byte. Operating on bits in these CPUs require additional processing.

We can use a bool in this manner

#define bool int #define TRUE 1 #define FALSE 0

or use typedefs.

But my question is this: why wasn't it implemented as a data type in C, even after so many years. doesn't it make sense to implement a one byte data type to store a boolean value rather than using int or short explicitly.

Related: stackoverflow.com/questions/1608318/is-bool-a-native-c-type/… — P.P
– P.P, Commented Sep 22, 2014 at 13:04
i looked inside <stdbool.h> but that uses integer as a return type. why integer, wont 4 bytes be redundant (considering sizeof(int) = 4), if we can do that using just 1 byte — Haris
– Haris, Commented Sep 22, 2014 at 13:04
@ralph - sizeof(bool) depends on the implementation, but if you're in C99 mode, sizeof(bool) is typically equal to 1. I answered a similar question long ago: stackoverflow.com/a/10630231/297696. Older implementations may keep sizeof(bool) == sizeof(int) (or whatever) for compatibility reasons. — wkl
– wkl, Commented Sep 22, 2014 at 13:07
@mafso example - bool b = (x & 0x8000); . If bool is an alias for char then this will set it to false even if the intended bit is set. This problem is more insidious for a function that takes bool as parameter, or returns bool. — M.M
– M.M, Commented Sep 23, 2014 at 21:42

Yu Hao · Accepted Answer · 2014-09-22 13:20:40Z

That's not true any more. The built-in boolean type, aka _Bool is available since C99. If you include stdbool.h, its alias bool is also there for you.

_Bool is a true native type, not an alias of int. As for its size, the standard only specifies it's large enough to store 0 and 1. But in practice, most compilers do make its size 1:

For example, this code snippet on ideone outputs 1:

#include <stdio.h> #include <stdbool.h> int main(void) { bool b = true; printf("size of b: %zu\n", sizeof(b)); return 0; }

i got this. but again the thing that comes in my mind is why will it return integer. the data type _Bool could have had its own native type which would take up only 1 Byte.
because the smallest addressable memory element size is 1 byte, so they can't make it 1 bit or less than 1 byte, unless its address aren't gonna be taken

Shafik Yaghmour · Accepted Answer · 2014-09-22 14:03:33Z

C99 added support for boolean type _Bool, is not simply a typedef and does not have to be the same size as int, from the draft C99 standard section 6.2.5 Types:

An object declared as type _Bool is large enough to store the values 0 and 1.

We have convenience macros through the stdbool.h header. we can see this from going to the draft C99 standard section 7.16 Boolean type and values whcih says:

The header defines four macros.

The macro

bool

expands to _Bool.

The remaining three macros are suitable for use in #if preprocessing directives. They are

true

which expands to the integer constant 1,

false

which expands to the integer constant 0, and

__bool_true_false_are_defined

which expands to the integer constant 1.

i got this. but again the thing that comes in my mind is why will it return integer. the data type _Bool could have had its own native type which would take up only 1 Byte.

Varun · Accepted Answer · 2019-10-20 06:40:12Z

Since the data types are predefined ,we cannot use the "bool" data type as it is not present in the documentation

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