C# - Buffer.BlockCopy Example

Buffer. The C# Buffer type handles ranges of bytes. It includes the optimized Buffer.BlockCopy method—this copies a range of bytes from one array to another.

Buffer methods. The Buffer class also provides the ByteLength, GetByte and SetByte methods. Usually BlockCopy is the most interesting.

Array.Copy

Array

BlockCopy. To begin, Buffer.BlockCopy does not copy logical elements in arrays. Instead it copies bytes. We call it to copy the bytes in one byte array to another.

Note This is useful for compression, images, or many other types of binary data.

byte, sbyte

Here The ints are used as bytes, not 4-byte ints. The byte array arr2 is automatically initialized to all zero bytes.

byte Array

using System; class Program { static void Main() { byte[] arr1 = new byte[] { 1, 2, 3, 4, 5 }; byte[] arr2 = new byte[10]; // Copy the first five bytes from arr1 to arr2 Buffer.BlockCopy(arr1, 0, arr2, 0, 5); Display(arr2); } static void Display(byte[] arr) { for (int i = 0; i < arr.Length; i++) { Console.Write(arr[i]); } Console.WriteLine(); } }

1234500000

Example 2. Buffer.BlockCopy can act on a data type that is not 1 byte. An int is 4 bytes. The fifth parameter of Buffer.BlockCopy is the number of bytes to copy.

Note We need to pass in the number of bytes to copy, not the array element count. We must multiply it by 4, or the size of int.

Note 2 In this example, the sizeof operator returns the byte length of a primitive data type like int. Here it returns 4.

And The multiplication of size of int times 4 can be resolved by the C# compiler—it won't cause any slowdowns.

using System; class Program { static void Main() { int[] arr1 = new int[] { 1, 2, 3, 4, 5 }; int[] arr2 = new int[10]; // Copy the first twenty bytes from arr1 to arr2 Buffer.BlockCopy(arr1, 0, arr2, 0, 5 * sizeof(int)); Display(arr2); } static void Display(int[] arr) { for (int i = 0; i < arr.Length; i++) { Console.Write(arr[i]); } Console.WriteLine(); } }

1234500000

ByteLength. ByteLength returns the byte count for an array. In this example there are 2 arrays—an integer array and a byte array—allocated on the managed heap.

Note We use Buffer.ByteLength to count the total number of bytes in each array. Each int is 4 bytes. Each byte is a single byte.

using System; class Program { static void Main() { // Example arrays for program. // ... Each array has three elements. int[] array1 = { 1, 2, 3 }; byte[] array2 = { 1, 2, 3 }; // Get lengths of arrays. // ... This counts the bytes in all elements. int length1 = Buffer.ByteLength(array1); int length2 = Buffer.ByteLength(array2); // Write results. Console.WriteLine(length1); Console.WriteLine(length2); } }

12 3

GetByte, SetByte. Next we use Buffer.GetByte and SetByte. We have an array of 3 integer values (an int array). Note that integers (int variables) in C# code are represented by 4 bytes.

int Array

int

Note By using GetByte and SetByte, we read and assign the individual bytes in each integer directly.

Tip This changes the decimal representation of the integer by changing the bytes in the integer.

And This is used to treat an integer array as a bit mask or other structure. One bit is used to indicate true or false.

true, false

using System; class Program { static void Main() { // Use an array of three integers for testing. // ... Loop through the bytes in the array and write their values. int[] array1 = { 1, 1, 256 }; for (int i = 0; i < Buffer.ByteLength(array1); i++) { Console.WriteLine(Buffer.GetByte(array1, i)); } // Set certain byte values at indexes in the array. Buffer.SetByte(array1, 0, 55); Buffer.SetByte(array1, 4, 55); Buffer.SetByte(array1, 8, 55); // Render the modified array. Console.WriteLine("---"); for (int i = 0; i < Buffer.ByteLength(array1); i++) { Console.WriteLine(Buffer.GetByte(array1, i)); } } }

1 0 0 0 1 0 0 0 0 1 0 0 --- 55 0 0 0 55 0 0 0 55 1 0 0

Benchmark BlockCopy, Array.Copy. To test Buffer.BlockCopy further, we benchmarked it on a 1000-element array. We compare it with the C# Array.Copy method.

Version 1 This version of the code uses Buffer.BlockCopy on a 1000-element byte array. It tests the result for correctness.

Version 2 This version uses Array.Copy with similar arguments to the Buffer.BlockCopy version.

Result In .NET 5 for Linux, using Buffer.BlockCopy and Array.Copy have the same performance on an int array.

Also The order of the tests matters here—try reordering the test for more details.

using System; using System.Diagnostics; class Program { static byte[] GetSourceArray() { // Populate data. var result = new byte[1000]; result[0] = 100; result[999] = 1; return result; } static bool IsValidData(byte[] data) { // Test data. return data[0] == 100 && data[999] == 1; } const int _max = 10000000; static void Main() { const int size = 1000; byte[] source = GetSourceArray(); byte[] target = new byte[size]; // Version 1: use Buffer.BlockCopy. var s1 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { Buffer.BlockCopy(source, 0, target, 0, size); if (!IsValidData(target)) { return; } } s1.Stop(); // Reset. source = GetSourceArray(); target = new byte[size]; // Version 2: use Array.Copy. var s2 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { Array.Copy(source, target, size); if (!IsValidData(target)) { return; } } s2.Stop(); Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns")); Console.WriteLine(((double)(s2.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns")); } }

23.49 ns Buffer.BlockCopy 24.56 ns Array.Copy

BitConverter. With this class we can change representations of value types. The BitConverter is sometimes used alongside Buffer.BlockCopy in programs that handle low-level data.

BitConverter

A summary. The Buffer type contains low-level methods that act upon bytes. A buffer is a range of bytes. With BlockCopy, we optimize large array copies of value types.