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); 

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.

Expression

Constant value

sizeof(sbyte)

1

sizeof(byte)

1

sizeof(short)

2

sizeof(ushort)

2

sizeof(int)

4

sizeof(uint)

4

sizeof(long)

8

sizeof(ulong)

8

sizeof(char)

2 (Unicode)

sizeof(float)

4

sizeof(double)

8

sizeof(decimal)

16

sizeof(bool)

1

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.

    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.
    */

For more information, see the C# Language Specification. The language specification is the definitive source for C# syntax and usage.

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