C# - String Literal - Dot Net Perls

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.

string.Empty

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.

string.Concat

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.