String.Concat. With concat, strings are merged (combined). It is possible to concatenate 2 or more strings with several syntax forms in the C# language.
Syntax notes. We use the plus operator and the string.Concat method. The plus compiles into string.Concat. Another option is string.Join.
using System;
// ... Create a new string reference.// It points to the literal.
string s1 = "string2";
// ... Add another string to the start.
string s2 = "string1" + s1;
Console.WriteLine(s2);string1string2
Two strings. This example shows combining 2 strings with string.Concat. It is the same as using plus. Usually, calling string.Concat directly results in less clear code.
Tip The main reason to use "+" instead of string.Concat is readability. Both expressions will compile into the same code.
Three strings. Here we use the same string.Concat or plus operator. You can use the + in any order, just like method arguments—which essentially is what the operands become.
Info Adding to the start is called prepending. You can append strings by using + or string.Concat.
using System;
string s1 = "string1";
string s2 = "string2";
// Combine 3 strings.
string s3 = s1 + s2 + "string3";
// Write the result to the screen.
Console.WriteLine(s3);string1string2string3
List. We create a List instance and add 3 string literals to it. We can pass the List variable reference to the string.Concat method. It will concatenate all the strings with no separator.
Note The string.Concat method here is equivalent to the string.Join method invocation with an empty separator.
using System;
using System.Collections.Generic;
// Create list of 3 strings.
var list = new List<string>();
list.Add("cat");
list.Add("dog");
list.Add("perls");
// Concat the list.
string concat = string.Concat(list);
Console.WriteLine(concat);
// Join the list.
string join = string.Join("", list);
Console.WriteLine(join);catdogperls
catdogperls
Benchmark, Concat. Sometimes we can use Concat (or the plus operator) or string.Format. Should we prefer Concat or Format when we have the choice?
Version 1 This version of the code uses Concat to combine 3 strings together into 1 string.
Version 2 Here we use string.Format, and a format string with 3 substitution markers, to combine the strings.
Result The plus operator (which is the Concat method) is faster. We should avoid Format unless more advanced features are needed.
using System;
using System.Diagnostics;
const int _max = 1000000;
string value1 = "bird";
string value2 = "frog";
string value3 = "dog";
var s1 = Stopwatch.StartNew();
// Version 1: use string.Concat.
for (int i = 0; i < _max; i++)
{
string result = value1 + value2 + value3;
if (result == null)
{
return;
}
}
s1.Stop();
var s2 = Stopwatch.StartNew();
// Version 2: use string.Format.
for (int i = 0; i < _max; i++)
{
string result = string.Format("{0}{1}{2}", value1, value2, value3);
if (result == null)
{
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")); 34.33 ns +
124.46 ns string.Format
Performance, overloads. In the .NET Framework, there are Concat methods that accept between 2 and 4 parameters. And there is one that accepts an array.
Info Looking into IL Disassembler, we see a list of many Concat methods. When 5 arguments are needed, the params version is used.
Thus It may be faster to perform concatenations of at most 4 strings at a time. But usually using StringBuilder is a better choice.
Notes, internals. The internals use ConcatArray, which seems to have a different implementation. This overload does not perform as well as the ones with fewer parameters.
StringBuilder. If you have a loop or could have many more than 5 strings, use StringBuilder. This may perform worse, but it will prevent edge cases from causing problems.
Notes, implementation. Should we use string.Concat or string.Join? The implementations .NET are the same except string.Join repeatedly appends the separator.
Note Appending an empty string is fast, but not doing so is even faster, so the string.Concat method would be superior here.
Tip The string.Concat method in .NET has an overload that receives an IEnumerable collection of type string.
Strings are frequently combined (concatenated). The benchmarks here give some data data points about what statements are most efficient.
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 May 25, 2023 (edit).
