Strings

A sequence of UTF-16 code units.
Stored internally as a sequential read-only collection of Char objects.

• Length property represents the number of Char objects contained, not the number of code units.
• To access the individual code points, use StringInfo

The string keyword looks like a type but is actually an alias for the type String

Empty Strings

Empty strings are represented as ""
However, to create empty strings, use the constant String.Empty This avoids null reference exceptions.

Comparisons

Case-sensitive, Ordinal Comparisons

• String.Equals
• == (String.Equality)
• != (String.Inequality)

Case-insensitive, Ordinal Comparisons

string1.Equals(string2, StringComparison.OrdinalIgnoreCase)  
String.Compare(string1, string2, StringComparison.OrdinalIgnoreCase)  

Constructing

string x = null;
string x = String.Empty;
char[] letters = { 'A', 'B', 'C' };
string x = new string(letters); // Use the constructor only when creating a string from a char, char[], or sybte.
string x = "str";

Accessing

Use String.IsNullOrEmpty(string) to verify the value of a string before accessing it.

Formatted Strings

Use string.Format() for formatted strings:

string result = string.Format("{0} and {1}", var1, var2)

Interpolated Strings

String interpolation achieves the same results as string formatting.

Availability: C#11: Newlines are permitted in string interpolations.

Use $ for interpolated strings: interpolationExpression,alignment:formatString

Alignment

Alignment is expressed as a signed integer n indicating preferred field width.
If n is less than the length of the string, it is ignored.
If n is positive, the field is right-aligned.
If n is negative, the field is left-aligned.

Formats

Numeric Formats

Currency:

• {var1:C}

Dates:

• {var1:d} (mm/dd/yyyy)
• {var1:D} (dayname, month dd, yyyy)

Times:

• {var1:t} (h:mm AM)
• {var1:T} (h:mm:ss AM)

Numbers:

• {var1:N} (thousands separators, 2 digits of precision)
• {var1:N4} (thousands separators, 4 digits of precision)

Percentage:

• {var1:P2} (2 digits of precision)

Ternary operator in interpolated expression

Since : has special meaning in interpolation expressions, when using it as the conditional operator, wrap it in parentheses:

$"My house is: {(a < 1 ? "red" : "blue")}"

Verbatim Strings

Verbatim strings will keep their whitespace and print escapes verbatim:

Console.WriteLine(@" c:\source\repos(this is where your code goes)");

Verbatim and interpolated strings can be combined.

Use double quotation marks to embed a literal quotation mark in a verbatim string.

Raw String Literals

Availability: C# 11

Raw string literals eliminate all need to escape content. They:

• Start with at least three quotes (""")
• End in the same number of quotes

Newlines following the opening quote and preceding the closing quote are not included in the content.

Raw String Literals and String Interpolation

Use multiple $ characters to denote how many consecutive braces start/end an interpolation.
In this example, two braces start/end an interpolation and the third is printed:

var location = $$"""
    You are at {{{Longitude}}, {{Latitude}}}
""";

UTF-8 String Literals

Availability: C# 11
By default, strings in .NET are stored in UTF-16 encoding. To encode a string as UTF-8, suffix it with u8:

ReadOnlySpan<byte> AuthWithTrailingSpace = new byte[] { 0x41, 0x55, 0x54, 0x48, 0x20 };
ReadOnlySpan<byte> AuthStringLiteral = "AUTH "u8;
byte[] AuthStringLiteral = "AUTH "u8.ToArray();

Notes:

• UTF-8 string literals cannot be combined with string interpolation.
• UTF-8 string literals cannot be used as the default value for an optional parameter (they are runtime constants, not compile-time constants).

Unicode Escape Sequences

\unnnn

Encoding / Decoding Strings

string someString = "This is some string.";
Encoding encoder = Encoding.ASCII; // Or .UTF7, .UTF8, .Unicode, .UTF32, .Default (which is UTF-8)
byte[] encoded = encoder.GetBytes(someString); // Encode the string into a byte array.
encoded.Length; // Returns the number of bytes the encoding needed.
string decoded = encoder.GetString(someString); // Decode the byte array back into a string.

Properties

• Length — Return the length of the string.

Methods

• String.IsNullOrEmpty(string) — Boolean if string is null or empty.
• String.IsNullOrWhiteSpace(string) — Boolean if string is null or whitespace.
• String.Join("sep", collection) — Concatenates elements of collection and separates each with sep.
• String.Concat(str1, str2) — Concatenates two string variables. Same as + operator.
  • .NET creates a new string in memory. Poor performance in loops.

Searching

• Contains("substr") — Boolean if str is in string.
• StartsWith("substr") — Boolean if string starts with str.
• EndsWith("substr")
• IndexOf("substr") — Return the index of the first occurrence of substr in string.
• LastIndexOf("substr") — Return the index of the last occurrence of substr in string.
• IndexOfAny("substr") — Return the index of the first occurrence of any of substr where substr is a comma-separated list.
• Substring(s, n) — Return the substring at starting index s extending for n characters.

Manipulating

All methods and operators that appear to modify a string actually — return a new string object.

• Insert
• Remove(s, n) — Remove the substring starting at index s for n characters.
• Replace("substr1", "substr2", ignoreCase=) — Replace substr1 with substr2.
  • ignoreCase is boolean and optional.
  • If substr2 is null, all occurrences of substr1 are removed.
• Split("delim", options) — Returns a string array containing subsets of the string split at delim.
  • options can be StringSplitOptions.RemoveEmptyEntries and TrimEntries
• ToCharArray() — Convert the string to a character array
  • This allows you to use array methods like Reverse()
• ToLower() — Return a lowercased string.
• ToUpper() — Return an uppercased string.
• Trim('c') — Return a string with character c trimmed.

Whitespace

• PadLeft(n, char) — Add n spaces to the left. Optionally, use char instead of spaces.
• PadRight(n, char)
• TrimStart() — Return a string with leading whitespace trimmed.
• TrimEnd() — Return a string with trailing whitespace trimmed.
• Trim() — Return a string with leading and trailing whitespace trimmed.

Determine if String Represents Numeric Value

Use TryParse methods of numeric types.