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r18ul
r18ul

Reputation: 1064

Why should I typedef enum when I use it as function return type or argument

I want to use enum as function return type or as a argument. But when I give it as is, it's giving error message. But if I typedef the same, it's working fine.

#include <stdio.h>

enum        // if *typedef enum* is used instead, it's working fine
{
    _false,
    _true,
} bool;

bool func1(bool );

int main()
{
    printf("Return Value = %d\n\n", func1(_true));

    return 0;
}

bool func1(bool status)
{
    return status;
}

Please help me understand this. Thank you.

Upvotes: 0

Views: 1270

Answers (4)

CCoder
CCoder

Reputation: 2335

Syntax you have used is wrong. Use it as below.

#include <stdio.h>

enum bool        // if *typedef enum* is used instead, it's working fine
{
    _false,
    _true,
} ;

enum bool func1(enum bool );

int main()
{
    printf("Return Value = %d\n\n", func1(_true));

    return 0;
}

enum bool func1(enum bool status)
{
    return status;
}

Instead if you use typedef you can directly use bool instead of enum bool.

Also to quote C99 standard:

Section 7.16 Boolean type and values < stdbool.h >

1 The header <stdbool.h> defines four macros.
2 The macro
bool expands to _Bool.
3 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.
4 Notwithstanding the provisions of 7.1.3, a program may undefine and perhaps then redefine the macros bool, true, and false.

If you have a compiler which compiles to C99 standard then you can just include stdbool.h and use bool like bool b = true;.

Upvotes: 1

Pubby
Pubby

Reputation: 53047

You've got the syntax wrong.

If you're not using typedef then it should be this:

enum bool
{
    _false,
    _true,
};
enum bool func1(enum bool );

enum bool func1(enum bool status)
{
    return status;
}

Upvotes: 4

ecatmur
ecatmur

Reputation: 157364

This code:

enum
{
    _false,
    _true,
} bool;

declares a variable bool of an anonymous enum type. typedef enum { ... } bool; defines a type called bool that can be used to refer to the enum type.

You can also write

enum bool
{
    _false,
    _true,
};

but then you have to refer to the type as enum bool. The most portable solution is to write

typedef enum bool
{
    _false,
    _true,
} bool;

i.e. defining an enum type called bool and a general type called bool that refers to it.

Upvotes: 4

Some programmer dude
Some programmer dude

Reputation: 409196

You are not making a new type bool, instead you are declaring a variable named bool.

Upvotes: 4

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