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Difference between Structure and Union

Difference between Structure and Union

As two of the most important keywords in C++, it’s important to understand the difference between structure and union. Structures are used to create class-like data types, while unions allow you to store multiple values in a single variable. In this blog post, we’ll take a look at some examples so you can see how they work in practice.

What is Structure?

  • Structure in programming is the arrangement of code in a project. Good structure makes code easy to read, understand, and maintain. It can also make code more efficient and less error-prone.
  • There are many different ways to arrange code, but some common approaches include grouping related code together, using consistent naming conventions, and comments.
  • Structure is often determined by the programming language being used, the type of project, and the preferences of the programmer. However, all good code should be structured in a way that makes it easy to read and understand. Poorly structured code can be difficult to work with and can lead to errors and inefficiencies. Therefore, it is important to take the time to think about the best way to arrange your code before you start writing it.

What is Union?

Union is data type that allows to store different data types in the same memory location. Union allows this by giving each data type its own section of the Unionvariable’s memory. The Union then just points to the currently used data type. This can be very useful if you want to save memory space or if you want to manipulate more than one data type at a time.

Union variables can only store one data type at a time though, so you have to make sure that you only use Union when you need it. If you try to store two different data types in a Union, then the Union will just point to the first data type that was stored in it and the second data type will be lost.

Difference between Structure and Union

Structure refers to the grouping of data elements of different data types that together represent a single record. A structure creates a data type that can be used to store a group of variables of different data types. Structure member is accessed by using the dot operator (.). The structure is also called a Record. It is mainly used in storing database records. It allocates memory for all members at compile time. The size of the memory for Structure = sum of sizes of all members. The structure is declared using the “struct” keyword.

  • A union is a special data type available in C that allows storing of different data types in the same memory location. Only one member can be stored in a union variable at any given time. When one member is stored, the union variable occupies enough memory to hold the largest member. The standard layout rule of C applies to unions as well.
  • Union variables can be initialized just like Structure variables but cannot be assigned until all members are assigned values. Union variables are declared using the “union” keyword. Union is mainly used when we want our program to use only one variable for various different data types i.e save memory space by storing various data types in the same memory address location.
  • While accessing union variables, we use the dot operator just like structures but structure members are accessed by their names while union members are accessed by their instance names due to which it becomes difficult sometimes to understand from code whether a particular variable is Structure or Union member unless both Structure and Union have been declared before that particular line of code where Structure or Union variables are being accessed using the dot operator (.).

Hence, care must be taken while declaring Structure and Union variables so that there is no scope of confusion for anyone reading our code. We must use Comments wherever required to make our code more user-friendly and easy to understand by others.


In the world of programming, a union is a data type that can hold any number of different data types. For example, you could have a variable that is of type Union(string, int) and it would be able to store either a string or an integer. A structure, on the other hand, is a data type that can only store one type of data. So, if you had a variable that was of type Structure(string), it could only store strings and not integers. The main difference between unions and structures is that unions are more versatile because they can store multiple types of data while structures can only store one type.

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