C# Default Access Modifiers: internal or private?

What is the Default Access Modifier in C#?

In C#, if you omit access modifiers when declaring class, struct, or field, the compiler applies a default. Understanding what these defaults are helps you avoid unintentional access issues in your code.

Default for class and struct: internal

When you declare a class or struct without specifying an access modifier, C# considers it internal by default. That means it is accessible only within the same project.

// Default is internal
struct MyStruct { }
class MyClass { }

What does “same project” mean?

Each project in a solution compiles into its own .dll or .exe, known as an assembly. The internal keyword means that other projects—even in the same solution—cannot access the type.

  • Same project: can access internal types
  • Different project in same solution: cannot access internal types

Example project structure

MySolution/
├── ProjectA   ← declares internal struct
└── ProjectB   ← references ProjectA

// In ProjectA
struct MyStruct { } // treated as internal

Here, MyStruct is usable in ProjectA but not in ProjectB, even though both belong to the same solution.

Default for fields: private

Fields inside a class or struct default to private if no access modifier is given. That means they are only accessible from inside the type itself.

struct MyStruct
{
    int x; // private by default
    int y; // also private
}

Fields are private by default — remember this when designing public APIs or exposing data.

Summary

  • class and struct default to internal
  • field defaults to private
  • internal = only visible inside the same project (assembly)

While you can rely on defaults, it's a good habit to explicitly specify access modifiers for clarity and maintainability.

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