Structures, Unions and Enumerations in C++
Last Updated : 21 May, 2025
Structures, unions and enumerations (enums) are 3 user defined data types in C++. User defined data types allow us to create a data type specifically tailored for a particular purpose. It is generally created from the built-in or derived data types. Let's take a look at each of them one by one.
Structure
In C++, structure is a user-defined data type that is used to combine data of different types. It is similar to an array but unlike an array, which stores elements of the same type, a structure can store elements of different data types. C++ structures can also have member functions to manipulate its data.
Create Structure
A structure has to be defined before being usable in the program. It is defined using struct keyword.
C++ struct structure_name{ type1 member1; type2 member2; . . typeN memberN; }; This definition does not allocate any memory to the structure. We have to crate structure variables separately to use it.
C++ We can also assign some values to the members:
C++ struct structure_name = {val1, val2, ..., valN}; Access and Update
Structure members can be accessed using the dot operator (.)
C++ struct structure_name; // Accessing first member structure_name.member1; // Accessing second member structure_name.member2; // Accessing third member structure_name.member3;
Example
C++ #include <bits/stdc++.h> using namespace std; // Define structure struct GFG { int G1; char G2; float G3; }; int main() { // Create object of structure GFG Geek = {85, 'G', 989.45}; // Accessing structure members values cout << Geek.G1 << endl; cout << Geek.G2 << endl; cout << Geek.G3; return 0; } Explanation: In the above code, values: (85, 'G', 989.45) are assigned to the G1, G2, and G3 member variables of the structure GFG, and these values are printed at the end using dot (.) operator.
Union
In C++, union is a user-defined datatype in which we can define members of different types of data types just like structures but unlike a structure, where each member has its own memory, a union member shares the same memory location.
Create Union
Union is first defined using union keyword:
C++ union union_name{ type1 member1; type2 member2; . . typeN memberN; }; Then we can create union variables:
C++ Access and Update
Only one member of a union stores memory at one time.
C++ Example
C++ #include <iostream> using namespace std; // Defining a Union union GFG { int G1; char G2; float G3; }; int main() { // Create an object of GFG union GFG Geek; // Assign union's member variables Geek.G1 = 85; // Accessing union members values cout << Geek.G1 << endl; Geek.G2 = 'G'; cout << Geek.G2 << endl; Geek.G3 = 989.45; cout << Geek.G3; return 0; } Enumeration
In C++, enumeration (enum) is a user-defined type that consists of a set of named integral constants. Enumerations help make the code more readable and easier to maintain by assigning meaningful names to constants.
Create Enums
Just like all other user defined data types, enums also needs to be defined before we can use it.
C++ enum enum_name { value1, value2, value3…..valueN }; Once defined, it can be used in the C++ program.
C++ enum_name var_name = value
This value should be taken from the defined value.
Example
C++ #include <bits/stdc++.h> using namespace std; int main() { // Defining enum Gender enum GFG { Male, Female }; // Creating GFG type variable and assigning // value GFG Geek = Male; switch (Geek) { case Male: cout << "Who is he?"; break; case Female: cout << "Who is she?"; break; default: cout << "Who is they?"; } return 0; } Similar Reads
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