String

Introduction#

A string is in effect a read-only slice of bytes. In Go a string literal will always contain a valid UTF-8 representation of its content.

Syntax#

• variableName := “Hello World” // declare a string
• variableName := `Hello World` // declare a raw literal string
• variableName := “Hello ” + “World” // concatenates strings
• substring := “Hello World”[0:4] // get a part of the string
• letter := “Hello World”[6] // get a character of the string
• fmt.Sprintf(“%s”, “Hello World”) // formats a string

String type

The string type allows you to store text, which is a series of characters. There are multiple ways to create strings. A literal string is created by writing the text between double quotes.

text := "Hello World"

Because Go strings support UTF-8, the previous example is perfectly valid. Strings hold arbitrary bytes which does not necessarily mean every string will contain valid UTF-8 but string literals will always hold valid UTF-8 sequences.

The zero value of strings is an empty string "".

Strings can be concatenated using the + operator.

text := "Hello " + "World"

Strings can also be defined using backticks ``. This creates a raw string literal which means characters won’t be escaped.

text1 := "Hello\nWorld"
text2 := `Hello
World`

In the previous example, text1 escapes the \n character which represents a new line while text2 contains the new line character directly. If you compare text1 == text2 the result will be true.

However, text2 := `Hello\nWorld` would not escape the \n character which means the string contains the text Hello\nWorld without a new line. It would be the equivalent of typing text1 := "Hello\\nWorld".

Formatting text

Package fmt implements functions to print and format text using format verbs. Verbs are represented with a percent sign.

General verbs:

%v    // the value in a default format
      // when printing structs, the plus flag (%+v) adds field names
%#v   // a Go-syntax representation of the value
%T    // a Go-syntax representation of the type of the value
%%    // a literal percent sign; consumes no value

Boolean:

%t    // the word true or false

Integer:

%b    // base 2
%c    // the character represented by the corresponding Unicode code point
%d    // base 10
%o    // base 8
%q    // a single-quoted character literal safely escaped with Go syntax.
%x    // base 16, with lower-case letters for a-f
%X    // base 16, with upper-case letters for A-F
%U    // Unicode format: U+1234; same as "U+%04X"

Floating-point and complex constituents:

%b    // decimalless scientific notation with exponent a power of two,
      // in the manner of strconv.FormatFloat with the 'b' format,
      // e.g. -123456p-78
%e    // scientific notation, e.g. -1.234456e+78
%E    // scientific notation, e.g. -1.234456E+78
%f    // decimal point but no exponent, e.g. 123.456
%F    // synonym for %f
%g    // %e for large exponents, %f otherwise
%G    // %E for large exponents, %F otherwise

String and slice of bytes (treated equivalently with these verbs):

%s    // the uninterpreted bytes of the string or slice
%q    // a double-quoted string safely escaped with Go syntax
%x    // base 16, lower-case, two characters per byte
%X    // base 16, upper-case, two characters per byte

Pointer:

%p    // base 16 notation, with leading 0x

Using the verbs, you can create strings concatenating multiple types:

text1 := fmt.Sprintf("Hello %s", "World")
text2 := fmt.Sprintf("%d + %d = %d", 2, 3, 5)
text3 := fmt.Sprintf("%s, %s (Age: %d)", "Obama", "Barack", 55)

The function Sprintf formats the string in the first parameter replacing the verbs with the value of the values in the next parameters and returns the result. Like Sprintf, the function Printf also formats but instead of returning the result it prints the string.

strings package

• strings.Contains

  fmt.Println(strings.Contains("foobar", "foo")) // true
  fmt.Println(strings.Contains("foobar", "baz")) // false

• strings.HasPrefix

  fmt.Println(strings.HasPrefix("foobar", "foo")) // true
  fmt.Println(strings.HasPrefix("foobar", "baz")) // false

• strings.HasSuffix

  fmt.Println(strings.HasSuffix("foobar", "bar")) // true
  fmt.Println(strings.HasSuffix("foobar", "baz")) // false

• strings.Join

  ss := []string{"foo", "bar", "bar"}
  fmt.Println(strings.Join(ss, ", ")) // foo, bar, baz

• strings.Replace

  fmt.Println(strings.Replace("foobar", "bar", "baz", 1)) // foobaz

• strings.Split

  s := "foo, bar, bar"
  fmt.Println(strings.Split(s, ", ")) // [foo bar baz]

• strings.ToLower

  fmt.Println(strings.ToLower("FOOBAR")) // foobar

• strings.ToUpper

  fmt.Println(strings.ToUpper("foobar")) // FOOBAR

• strings.TrimSpace

  fmt.Println(strings.TrimSpace("  foobar  ")) // foobar

More: https://golang.org/pkg/strings/.