What are the fundamental differences between value types and reference types in C#?

In C#, the main difference between value types and reference types is in the way of data storage and memory management. 1. The value type directly contains data, usually stored on the stack, such as int, float, bool and struct, with fast access speed and short life cycle; the reference type stores references to the actual data, the object itself is stored on the heap, such as class, string or object, and the reference variables are stored on the stack, relying on garbage collection and cleaning. 2. Copy the actual value when the value type is assigned, and modifying the copy does not affect the original value; copy the reference address when the reference type is assigned, and the two variables point to the same object, and modification will affect each other. 3. The value type cannot be null by default unless nullable types such as int? are used; the reference type can naturally be null, indicating that it does not point to any object. 4. Value types are suitable for small, unchanged data, and have higher performance; reference types are suitable for complex, shared or variable data, but have heap allocation and GC overhead. When using it, you should select the appropriate type according to the scene and pay attention to the performance impact of boxing/unboxing.

In C#, the main difference between value types and reference types lies in how they store data and how memory is managed. Value types directly contain their data, while reference types store a reference to the actual data. This distinction affects performance, behavior when passed around, and how changes are handled.

1. Memory Allocation: Where the Data Lives

Value types are usually stored on the stack , which makes access faster and more efficient for small, short-lived variables. Examples include int , float , bool , and struct .

Reference types, like class , string , or object , are stored on the heap , and only the reference (or pointer) to that memory location is stored on the stack.

• Stack allocation is quick and cleaned up automatically when the method call ends.
• Heap allocation involves more overhead and relies on garbage collection to clean up unused objects.

So when you declare:

 int x = 10; // Value type - stored on the stack
string name = "Tom"; // Reference type - 'name' holds a reference to the string on the heap

You're working with two different memory models under the hood.

2. Assignment Behavior: Copying vs Referencing

When you assign one value type to another, it copies the actual value . So modifying one doesn't affect the other.

 int a = 5;
int b = a;
b = 10;
Console.WriteLine(a); // Still prints 5

But with reference types, assigning one variable to another copy the reference , not the object itself. That means both variables point to the same object in memory.

 Person p1 = new Person { Name = "Alice" };
Person p2 = p1;
p2.Name = "Bob";
Console.WriteLine(p1.Name); // Now prints "Bob"

This is a common source of confusion — especially when debugging unexpected changes.

3. Default Values ​​and Nullability

Value types cannot be null by default because they hold actual values. For example, an int will always have a value like 0 if not explicitly set.

However, C# allows nullable versions using ? :

 int? age = null; // Valid

Reference types can naturally be null , meaning the variable isn't pointing to any object:

 string message = null; // Common practice

Be careful though — accessing members of a null reference type causes a NullReferenceException .

4. Performance Considerations

Since value types are stored inline and copied when passed around, they're generally faster and more memory-efficient for small, immutable data. But passing large structs repeatedly can hurt performance due to copying.

Reference types are better suited for complex, shared, or mutable data — but come with the cost of heap allocation and garbage collection.

Here's a quick list of typical use cases:

• Use value types for simple data like numbers, flags, or small custom structures.
• Use reference types for objects with identity, behavior, or shared state.
• Prefer readonly struct for performance-sensitive code where immutability helps.
• Be cautious with boxing/unboxing — converting value types to object can cause performance hits.

Basically that's it. Understanding these differences helps you write more predictable and efficient C# code.

The above is the detailed content of What are the fundamental differences between value types and reference types in C#?. For more information, please follow other related articles on the PHP Chinese website!