sizeof (C# Reference)

Used to obtain the size in bytes for an unmanaged type. Unmanaged types include the built-in types that are listed in the table that follows, and also the following:

• Enum types

• Pointer types

• User-defined structs that do not contain any fields or properties that are reference types

The following example shows how to retrieve the size of an int:

// Constant value 4:
int intSize = sizeof(int); 

Remarks

Starting with version 2.0 of C#, applying sizeof to built-in types no longer requires that unsafe mode be used.

The sizeof operator cannot be overloaded. The values returned by the sizeof operator are of type int. The following table shows the constant values that are substituted for sizeof expressions that have certain built-in types as operands.

For all other types, including structs, the sizeof operator can be used only in unsafe code blocks. Although you can use the Marshal.SizeOf method, the value returned by this method is not always the same as the value returned by sizeof. Marshal.SizeOf returns the size after the type has been marshaled, whereas sizeof returns the size as it has been allocated by the common language runtime, including any padding.

Example

class MainClass
{
    // unsafe not required for primitive types. 
    static void Main()
    {
        Console.WriteLine("The size of short is {0}.", sizeof(short));
        Console.WriteLine("The size of int is {0}.", sizeof(int));
        Console.WriteLine("The size of long is {0}.", sizeof(long));
    }
}
/*
Output:
    The size of short is 2.
    The size of int is 4.
    The size of long is 8.
*/

C# Language Specification

For more information, see the following sections in the C# Language Specification:

• 18.5.8 The sizeof operator

See Also

Concepts

C# Programming Guide

Reference

C# Keywords

Operator Keywords (C# Reference)

enum (C# Reference)

Unsafe Code and Pointers (C# Programming Guide)

Structs (C# Programming Guide)

Constants (C# Programming Guide)

Other Resources

C# Reference

Change History