Struct vs Class in C#: Choosing the Right Data Type

In C#, there are two primary object types that developers can use to build their code: structs and classes. While these two types may seem similar at first glance, they have some key differences that set them apart from each other.

In this article, we'll explore what structs and classes are, their differences, and when to use them in your C# code. So let's dive in!

What are Structs and Classes?

In basic terms, a struct is a value type while a class is a reference type. Value types contain their data directly on the stack, while reference types store a reference to an object containing the data on the heap.

This difference is important because it affects how the objects are copied and passed around in memory.

Structs are often used to represent simple data types, such as integers, strings, and other basic data types. Classes, on the other hand, are used to represent more complex objects with multiple properties and methods.

Classes are typically used to model real-world objects, such as cars or people in a program.

Another important difference between structs and classes is that structs are value types, which means that they are copied when they are passed as arguments to methods or functions.

This can be useful in certain situations, such as when you want to create a copy of an object without modifying the original.

Additionally, structs are often used in performance-critical applications because they are more lightweight than classes. Since structs are stored on the stack, they can be accessed more quickly than objects stored on the heap

Difference Between Struct and Class in C#

One major difference between structs and classes is that structs are value types, while classes are reference types. This means that structs are copied by value when they are passed around, while classes are copied by reference.

When you pass a struct to a method, you’re passing a copy of the data. This can cause performance issues if you’re working with large structs.

Another difference is that structs cannot inherit from other structs, while classes can inherit from other classes. This allows you to create more complex object hierarchies with classes.

Additionally, structs are typically used for smaller, simpler data structures, while classes are used for more complex objects that require methods and properties.

Structs are often used for basic data types like integers, floats, and booleans, while classes are used for objects like cars, animals, and people.

Memory Allocation for Structs and Classes

When you create a struct, its memory is allocated on the stack. This makes structs more efficient than classes, which are allocated on the heap. This means that structs are more suitable for functions that require high performance and low memory usage.

One drawback of using structs is that they have a size limit of 16 bytes. If your struct’s size exceeds this limit, it will be allocated on the heap instead of the stack. This can cause performance issues if you’re working with large structs.

On the other hand, classes are allocated on the heap, which means they have no size limit. This makes them more suitable for complex data structures that require a large amount of memory.

However, this also means that classes are less efficient than structs and can cause performance issues if used in functions that require high performance and low memory usage.

Another advantage of using classes is that they support inheritance and polymorphism, which allows for more flexible and modular code. Structs, on the other hand, do not support inheritance or polymorphism and are limited to simple data structures.

Performance Comparison: Structs vs Classes

Due to their memory allocation differences, structs are generally faster than classes. If you’re working with a large amount of data, structs can be more efficient because they don’t require the overhead of heap memory allocation.

However, there are some cases where classes are faster than structs. For example, when copying large objects, classes can be more efficient because they only copy a reference to the object instead of the object itself.

Another advantage of using structs is that they are value types, meaning that they are copied by value rather than by reference. This can be useful in situations where you want to ensure that the original data is not modified by any subsequent operations.

On the other hand, classes are reference types, which means that they are passed by reference. This can be useful in situations where you want to modify the original data without creating a new copy of it.

When to Use Structs in C#

Structs are best used when you need to represent simple data types, such as integers, strings, or other basic data types. They are also useful when you need to work with large datasets, such as arrays or lists, where performance is critical.

You should also use a struct when you need to pass a small amount of data to a method, and you want to avoid the overhead of passing a reference to a class.

Another scenario where structs can be useful is when you need to create a lightweight object that doesn’t require inheritance or polymorphism. Since structs are value types, they can be easily copied and passed around without the need for complex memory management.

When to Use Classes in C#

Classes are best used when you need to represent more complex objects, such as real-world entities like cars, people, or animals. They are also useful when you need to create hierarchies of objects, where one class inherits from another.

You should also use a class when you need to work with large amounts of data, such as when you’re working with a database or other external data source.

Another situation where classes are useful is when you need to encapsulate functionality and data together. By creating a class, you can group related methods and properties into a single unit, making your code more organized and easier to maintain.

Additionally, classes can be used to implement interfaces, which define a set of methods that a class must implement. This allows for greater flexibility and modularity in your code.

Examples of Structs and Classes in C#

Here are some examples of how you might use structs and classes in a C# program:

Example 1: Representing a point:

struct Point
{
    public int X;
    public int Y;
}

class PointClass
{
    public int X;
    public int Y;
}

Example 2: Representing a person:

struct Person {
    public string Name;
    public int Age;
}

class PersonClass {
    public string Name;
    public int Age;
}

Example 3: Representing a date:

struct Date
{
    public int Day;
    public int Month;
    public int Year;
}

class DateClass
{
    public int Day;
    public int Month;
    public int Year;
}

Example 4: Representing a book:

struct Book
{
    public string Title;
    public string Author;
    public int Pages;
}

class BookClass
{
    public string Title;
    public string Author;
    public int Pages;
}

Best Practices for Using Structs and Classes in C#

When using structs, it’s important to keep their size small, so they’re stored on the stack instead of the heap. This can help to improve performance and reduce memory usage.

When using classes, it’s a good idea to use inheritance to create hierarchies of objects with shared properties and methods. This can help to reduce code duplication and make your code more maintainable.

Another important consideration when using structs and classes in C# is to use them appropriately based on their intended purpose. Structs are best used for small, simple data structures that don’t require a lot of functionality, while classes are better suited for more complex objects with behavior and functionality.

Common Mistakes to Avoid When Using Structs and Classes in C#

One common mistake when using structs is to make them too large. If your struct is too large, it will be stored on the heap instead of the stack, which can cause performance issues.

Another mistake is to use a class when a struct would be more appropriate. If you’re working with simple data types, using a struct can be more efficient and improve performance.

It’s also important to note that structs are value types, while classes are reference types. This means that when you pass a struct to a method or assign it to a variable, a copy of the struct is created. This can lead to unexpected behavior if you’re not careful.

Additionally, structs cannot inherit from other structs or classes, and they cannot be used as a base for other types. If you need to create a more complex data structure, a class may be a better choice.

Conclusion

Structs and classes are fundamental concepts in C#, and understanding the differences between them is critical when building your code. By understanding their differences, you can make informed decisions about when to use which type and how to optimize your code for performance and maintainability.

Comments

[Anthony Fung]

Thanks for the comprehensive review!

A minor note - the article image might have been intended for another post; it reads Abstract Class VS Interface.

One rule of thumb I learnt on helping to decide between the two is to use a struct if the properties can't be separated. E.g. a 2D point couldn't exist with only x and not y.

As mentioned in the article, classes are passed by reference. One common error I've seen is not realising that Lists (or other collections) containing classes will be shallow copied. Both lists will point to the same data, so modifying an object in one list modifies the object in the other list too. One way to prevent this is to deep clone the object; a common way of doing this is to serialize it to JSON and then deserialize it back again.

Also mentioned is that structs are passed by value, i.e. they are copied when passed around. If you need them to be passed by reference (i.e. have class-like passing behaviour), you can use ref to mark method parameters.