`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.

Info Newlines are specified with either "\r\n" or just "\n." And tabs are specified with "\t."

Next For quotes, we often use a backslash, but for a verbatim literal, we use two quotes to mean a quote.

Here Four of the string literals are prefixed with the "at" symbol. This is the verbatim string literal syntax.

Tip The C# compiler allows you to use real newlines in verbatim literals. You must encode quotation marks with double quotes.

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.

Next This program appears to concatenate 3 strings. When compiled the IL shows that only one string is used.

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.

Here String literal constants are separated and shared. Applying constant folding manually is not required for performance.

Detail If you use a certain string literal in many places in a program, it is stored only once in the user strings stream.

Thus We see the compiler technique of constant folding applied to string literals in C# programs.

A summary

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.

String literals