Enumeration (or enum) in C

In C, an enumeration (or enum) is a user defined data type that contains a set of named integer constants. It is used to assign meaningful names to integer values, which makes a program easy to read and maintain.

Definition

An enum must be defined before we can use it in program.

enum enum_name { 
    n1, n2, n3, ... 
};

where, n1, n2, n3, ... are names assigned to an integer value. By default, first name n1 is assigned 0, n2 is assigned 1 and the subsequent ones are incremented by 1.

Example:

enum calculate { 
    SUM, DIFFERENCE, PRODUCT, QUOTIENT
};

Here, the name SUM is automatically assigned 0, DIFFERENCE is assigned 1 and so on. Enum names should follow the standard C variable naming rules. Uppercase is preferred for easy identification.

Also, enum names must be be unique in their scope. For example, the below code fails as two enums items and calculate have same named integer PRODUCT.

enum calculate { 
    SUM, DIFFERENCE, PRODUCT, QUOTIENT
};

enum item{
    PRODUCT, SERVICE
}

Create enum Variables

After enum is defined, we can create variables of that enum by using its specified name.

enum_name v;

Initialization

An enum variable can be initialized either with a name defined in the enum definition or directly with its integer value.

#include <stdio.h>

// Defining enum
enum direction {
    EAST, NORTH, WEST, SOUTH
};

int main() {

    // Creating enum variable
    enum direction dir = NORTH;
    printf("%d\n", dir);
    
    // This is valid too
    dir = 3;
    printf("%d", dir);
    return 0;
}

1
3

Though it is recommended to avoid using integers as enums loses their purpose when integer values are preferred in the use.

Assign Values Manually

We can also manually assign desired values to the enum names as shown:

enum enum_name { 
    n1 = val1, n2 = val2, n3, ... 
};

It is not mandatory to assign all constants. The next name will be automatically assigned a value by incrementing the previous name's value by 1. For example, n3 here will be (val2 + 1). Also, we can assign values in any order, but they must be integer only.

Example:

#include <stdio.h>

// Defining enum
enum enm {
    a = 3, b = 2, c
};

int main() {

    // Creating enum variable
    enum enm v1 = a;
    enum enm v2 = b;
    enum enm v3 = c;
    printf("%d %d %d", v1, v2, v3);
    return 0;
}

3 2 3

In the above program, a is assigned the value 3, b is assigned 2, and c will automatically be assigned the value 3, as the enum values increment from the last assigned value. We can also confirm here that two enum names can have same value.

Size of Enums

Enum definition is not allocated any memory, it is only allocated for enum variables. Usually, enums are implemented as integers, so their size is same as that of int. But some compilers may use short int (or even smaller type) to represent enums. We can use the sizeof operator to check the size of enum variable.

Example:

#include <stdio.h>

// Defining enum
enum direction {
    EAST, NORTH, WEST, SOUTH
};

int main() {
    enum direction dir = NORTH;
    
    // Checking the size of enum
    printf("%ld bytes", sizeof(dir));
    return 0;
}

4 bytes

Enum and Typedef

The typedef keyword can be used to define an alias for an enum so that we can avoid using the keyword enum again and again.

Example:

#include <stdio.h>

// Defining enum
typedef enum direction {
    EAST, NORTH, WEST, SOUTH
}Dirctn;

int main() {
    Dirctn dir = NORTH;
    
    // Checking the size of enum
    printf("%d", dir);
    return 0;
}

1

In the above program, we have used typedef to create a nickname Dirctn for the direction enum so that we can directly refer to it by using the nickname. It enhances the code readability.

Applications of Enums in C

Enums are extensively used in various real-world applications in programming, such as:

• State Representation: Enums are commonly used to represent different states or modes in state machines, like in game development or process control systems.
• Error Codes: Enums are useful for defining a set of related error codes with meaningful names, making the code easier to debug and maintain.
• Menu Choices or User Inputs: Enums are useful for handling menu options or user input and can represent variety of user input such as days of the week.
• File Permissions: Enums are useful for handling file permissions in an operating system or file management system, with different permission levels such as READ, WRITE, and EXECUTE.

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Article Tags :

• C Language
• C Basics
• cpp-data-types
• C-Struct-Union-Enum