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C# CopyTo String Method: Put Chars in Array

Invoke the CopyTo method on the string type to copy a range of characters into a char array.

CopyTo

takes string characters and puts them into an array. It copies a group of characters from one source string into a character array of a certain size.Stringsstring.Copy

Optimized code.

This .NET Framework method provides optimized low-level code. When we need to copy chars from a string, CopyTo is a good solution.

To start,

CopyTo() must be called on an instance of a string object. String objects in C# can be represented by string literals, meaning "Literal".CopyTo() would be useful as well.String Literal

New: In this example, please notice how the char[] variable is allocated before CopyTo is invoked.

Char Array

Void: CopyTo() is void, and returns nothing. The char array in the program instead has its characters changed internally in CopyTo.

Note: Arrays are indexed by their offsets. The fourth character where the CopyTo method begins copying is the letter "N".

Then: That character and the two following characters are copied into the char[] buffer and the buffer's values are printed to the screen.

Console.WriteLine
C# program that uses CopyTo using System; class Program { static void Main() { // Declare a string constant and an output array. string value1 = "Dot Net Perls"; char[] array1 = new char[3]; // Copy the fifth, sixth, and seventh characters to the array. value1.CopyTo(4, array1, 0, 3); // Output the array we copied to. Console.WriteLine("--- Destination array ---"); Console.WriteLine(array1.Length); Console.WriteLine(array1); } } Output --- Destination array --- 3 Net

Internals.

In the .NET Framework, the CopyTo instance method on string is contained in an unsafe context, meaning it can access pointers directly.

However: Using CopyTo is reliable because it has been extensively tested. The unsafe code is not your responsibility.

Wstrcpy: The CopyTo method internally calls into wstrcpy, which is a heavily optimized and unrolled loop. It copies characters quickly.

Substring.

In most .NET programs, the CopyTo method is not necessary. Instead, your programs will often use Substring to copy one range of characters to another.Substring

But: CopyTo() along with ToCharArray can be used as optimizations. And CopyTo can help when char arrays are needed by other methods.

ToCharArray

A benchmark.

I wanted to know whether using CopyTo is faster than a for-loop on a short string. I found that the for-loop is faster. This of course depends on your system and other factors.

Important: For longer strings, the benchmark would need to be adjusted. Careful testing is needed.

Version 1: Copy chars from a string into a char array with CopyTo. Only 4 chars are copied.

Version 2: Copy those same 4 chars into the char array with a for-loop. Use an index expression to assign elements.

C# program that benchmarks CopyTo, for-loop using System; using System.Diagnostics; class Program { const int _max = 100000000; static void Main() { char[] values = new char[100]; var s1 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { "1234".CopyTo(0, values, 0, 4); // [CopyTo] } s1.Stop(); var s2 = Stopwatch.StartNew(); for (int i = 0; i < _max; i++) { for (int j = 0; j < "1234".Length; j++) // [For-loop] { values[j] = "1234"[j]; } } 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")); Console.Read(); } } Output 11.44 ns, CopyTo 8.64 ns, For-loop

A summary.

Copy() allows you to copy ranges of characters from a source string into target arrays. It is often not needed, but can replace a for-loop to copy chars.ArrayChar Array
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