BinaryWriter. This C# type creates binary files. A binary file uses a specific data layout for its bytes. The BinaryWriter type is ideal for creating these files.

BinaryReader

File

Type info. BinaryWriter is a stream-based mechanism for writing data to a file location on the disk. Here we see an example of using the BinaryWriter class, which will create the binary file.

An example. BinaryWriter writes data. It writes primitive types like int, uint or char. In this example, File.Open returns a stream that the BinaryWriter writes through to.

int

char

File.Open

Overload

using System.IO;

class Program
{
    static void Main()
    {
        W();
    }

    static void W()
    {
        // Create 12 integers.
        int[] a = new int[]
        {
            1,
            4,
            6,
            7,
            11,
            55,
            777,
            23,
            266,
            44,
            82,
            93
        };
        // Use using statement and File.Open.
        using (BinaryWriter b = new BinaryWriter(File.Open("file.bin", FileMode.Create)))
        {
            // Use foreach and write all 12 integers.
            foreach (int i in a)
            {
                b.Write(i);
            }
        }
    }
}

Close. The using statement will cause the Dispose method to be called. In the Dispose implementation, Close is called—an explicit Close call is not necessary.

using

Stream

.method family hidebysig newslot virtual
        instance void  Dispose(bool disposing) cil managed
{
  // Code size       15 (0xf)
  .maxstack  8
  IL_0000:  ldarg.1
  IL_0001:  brfalse.s  IL_000e
  IL_0003:  ldarg.0
  IL_0004:  ldfld      class System.IO.Stream
                           System.IO.BinaryWriter::OutStream
  IL_0009:  callvirt   instance void System.IO.Stream::Close()
  IL_000e:  ret
} // end of method BinaryWriter::Dispose

File data. What does the output file look like visually when you inspect it in an editor such as Visual Studio? It is not something easily read—it looks like random bytes.

Summary. BinaryWriter is an easy way to create a binary file. Ideal for certain file formats that your programs must support, the BinaryWriter is used in many projects around the world.