String literals

These are for constant string data in C# programs. String data is created in different ways. We use literals as arguments to methods, or anywhere a string is needed.

With a string literal, characters are stored directly inside the metadata. Fewer indirections (which reduces performance) are needed.

Example program

Here the class-level string literals are represented as static or const references. The method-level ones are treated separately in the metadata.

using System;

class Program
{
    static string _value1 = "String literal";
    const string _value2 = "String literal 2";
    const string _value3 = "String literal 3\r\nAnother line";
    const string _value4 = @"String literal 4
    Another line";
    const string _value5 = "String literal\ttab";
    const string _value6 = @"String literal\ttab";

    static void Main()
    {
        //
        // Execution engine begins here.
        //
        string test1 = "String literal \"1\"";
        const string test2 = "String literal 2";
        string test3 = @"String literal ""3""";
        const string test4 = @"String literal 4";
        //
        // Print out the string literals.
        //
        Console.WriteLine(
            "{0}\n{1}\n{2}\n{3}\n{4}\n{5}\n{6}\n{7}\n{8}\n{9}",
            _value1, _value2, _value3, _value4, _value5, _value6,
            test1, test2, test3, test4);
    }
}
String literal
String literal 2
String literal 3
Another line
String literal 4
Another line
String literal  tab
String literal\ttab
String literal "1"
String literal 2
String literal "3"
String literal 4

Raw string literals

It is also possible to use 3 quotes to start (or end) a raw string literal. This contains the inner characters exactly, but with left-side indentation removed.

using System;

class Program
{
    static void Main()
    {
        string text = """
        Hello friend,
        How are you?
        """;

        Console.WriteLine(text);
    }
}
Hello friend,
How are you?

Concat

Concatenating string variables is done at runtime. But if a string variable is constant, the compiler will generate intermediate language with the concatenations removed.

using System;

class Program
{
    static void Main()
    {
        const string a = "Dot ";
        const string b = "Net ";
        const string c = "Perls";
        Console.WriteLine(a + b + c);
    }
}
Dot Net Perls
.method private hidebysig static void  Main() cil managed
{
  .entrypoint
  // Code size       11 (0xb)
  .maxstack  8
  IL_0000:  ldstr      "Dot Net Perls"
  IL_0005:  call       void [mscorlib]System.Console::WriteLine(string)
  IL_000a:  ret
} // end of method Program::Main

Performance note

Before the string literals ever reach the metadata or the intermediate language instructions, the C# compiler applies an optimization called constant folding.

String literals are specified with the string verbatim syntax. We use the backslash to escape certain sequences. String literals are constant—they cannot be changed.