CopyTo. This C# method takes string characters and puts them into an array. It copies a group of characters from one source string into a character array.
Optimized code. This .NET string method provides optimized low-level code. When we need to copy chars from a string, CopyTo is a good solution.
An example. CopyTo() must be called on an instance of a string object. String objects in C# can be represented by string literals. So we can call CopyTo on a literal as well.
using System;
class Program
{
static void Main()
{
string value1 = "abcd";
char[] array1 = new char[3];
// Copy the final 3 characters to the array.
value1.CopyTo(1, array1, 0, 3);
// Print the array we copied to.
Console.WriteLine($"RESULT LENGTH = {array1.Length}");
Console.WriteLine(array1);
}
}RESULT LENGTH = 3
bcd
A benchmark. I wanted to know whether using CopyTo is faster than a for-loop on a short string. Should we use CopyTo in performance-critical methods?
Version 1 Copy chars from a string into a char array with CopyTo. Only 10 chars are copied.
Version 2 Copy those same 10 chars into the char array with a for-loop. Use an index expression to assign elements.
Result When tested in separate runs of the program on .NET 5 for Linux (in 2021), I find string CopyTo is faster.
Also CopyTo begins becoming much faster as the source string becomes longer. But even at 10 chars it is faster overall.
using System;
using System.Diagnostics;
class Program
{
const int _max = 100000000;
static void Main()
{
char[] values = new char[100];
string temp = "0123456789";
// Version 1: use CopyTo.// Version 2: use for-loop.
var s1 = Stopwatch.StartNew();
if (true)
{
for (int i = 0; i < _max; i++)
{
temp.CopyTo(0, values, 0, temp.Length);
}
}
else
{
for (int i = 0; i < _max; i++)
{
for (int j = 0; j < temp.Length; j++)
{
values[j] = temp[j];
}
}
}
s1.Stop();
Console.WriteLine(((double)(s1.Elapsed.TotalMilliseconds * 1000000) / _max).ToString("0.00 ns"));
}
} 7.38 ns, CopyTo
12.39 ns, For-loop
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.
A summary. CopyTo() 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.
Dot Net Perls is a collection of tested code examples. Pages are continually updated to stay current, with code correctness a top priority.
Sam Allen is passionate about computer languages. In the past, his work has been recommended by Apple and Microsoft and he has studied computers at a selective university in the United States.
This page was last updated on Mar 23, 2022 (image).
