Go: strings Index | Examples | Files

package strings

import "strings"

Package strings implements simple functions to manipulate UTF-8 encoded strings.

For information about UTF-8 strings in Go, see https://blog.golang.org/strings.

Index

Examples

Package Files

builder.go compare.go reader.go replace.go search.go strings.go strings_decl.go

func Compare Uses

❖
func Compare(a, b string) int

Compare returns an integer comparing two strings lexicographically. The result will be 0 if a==b, -1 if a < b, and +1 if a > b.

Compare is included only for symmetry with package bytes. It is usually clearer and always faster to use the built-in string comparison operators ==, <, >, and so on.

Example

Code:play  

fmt.Println(strings.Compare("a", "b"))
fmt.Println(strings.Compare("a", "a"))
fmt.Println(strings.Compare("b", "a"))

Output:

-1
0
1

func Contains Uses

❖
func Contains(s, substr string) bool

Contains reports whether substr is within s.

Example

Code:play  

fmt.Println(strings.Contains("seafood", "foo"))
fmt.Println(strings.Contains("seafood", "bar"))
fmt.Println(strings.Contains("seafood", ""))
fmt.Println(strings.Contains("", ""))

Output:

true
false
true
true

func ContainsAny Uses

❖
func ContainsAny(s, chars string) bool

ContainsAny reports whether any Unicode code points in chars are within s.

Example

Code:play  

fmt.Println(strings.ContainsAny("team", "i"))
fmt.Println(strings.ContainsAny("failure", "u & i"))
fmt.Println(strings.ContainsAny("foo", ""))
fmt.Println(strings.ContainsAny("", ""))

Output:

false
true
false
false

func ContainsRune Uses

❖
func ContainsRune(s string, r rune) bool

ContainsRune reports whether the Unicode code point r is within s.

Example

Code:play  

// Finds whether a string contains a particular Unicode code point.
// The code point for the lowercase letter "a", for example, is 97.
fmt.Println(strings.ContainsRune("aardvark", 97))
fmt.Println(strings.ContainsRune("timeout", 97))

Output:

true
false

func Count Uses

❖
func Count(s, substr string) int

Count counts the number of non-overlapping instances of substr in s. If substr is an empty string, Count returns 1 + the number of Unicode code points in s.

Example

Code:play  

fmt.Println(strings.Count("cheese", "e"))
fmt.Println(strings.Count("five", "")) // before & after each rune

Output:

3
5

func EqualFold Uses

❖
func EqualFold(s, t string) bool

EqualFold reports whether s and t, interpreted as UTF-8 strings, are equal under Unicode case-folding.

Example

Code:play  

fmt.Println(strings.EqualFold("Go", "go"))

Output:

true

func Fields Uses

❖
func Fields(s string) []string

Fields splits the string s around each instance of one or more consecutive white space characters, as defined by unicode.IsSpace, returning a slice of substrings of s or an empty slice if s contains only white space.

Example

Code:play  

fmt.Printf("Fields are: %q", strings.Fields("  foo bar  baz   "))

Output:

Fields are: ["foo" "bar" "baz"]

func FieldsFunc Uses

❖
func FieldsFunc(s string, f func(rune) bool) []string

FieldsFunc splits the string s at each run of Unicode code points c satisfying f(c) and returns an array of slices of s. If all code points in s satisfy f(c) or the string is empty, an empty slice is returned. FieldsFunc makes no guarantees about the order in which it calls f(c). If f does not return consistent results for a given c, FieldsFunc may crash.

Example

Code:play  

f := func(c rune) bool {
    return !unicode.IsLetter(c) && !unicode.IsNumber(c)
}
fmt.Printf("Fields are: %q", strings.FieldsFunc("  foo1;bar2,baz3...", f))

Output:

Fields are: ["foo1" "bar2" "baz3"]

func HasPrefix Uses

❖
func HasPrefix(s, prefix string) bool

HasPrefix tests whether the string s begins with prefix.

Example

Code:play  

fmt.Println(strings.HasPrefix("Gopher", "Go"))
fmt.Println(strings.HasPrefix("Gopher", "C"))
fmt.Println(strings.HasPrefix("Gopher", ""))

Output:

true
false
true

func HasSuffix Uses

❖
func HasSuffix(s, suffix string) bool

HasSuffix tests whether the string s ends with suffix.

Example

Code:play  

fmt.Println(strings.HasSuffix("Amigo", "go"))
fmt.Println(strings.HasSuffix("Amigo", "O"))
fmt.Println(strings.HasSuffix("Amigo", "Ami"))
fmt.Println(strings.HasSuffix("Amigo", ""))

Output:

true
false
false
true

func Index Uses

❖
func Index(s, substr string) int

Index returns the index of the first instance of substr in s, or -1 if substr is not present in s.

Example

Code:play  

fmt.Println(strings.Index("chicken", "ken"))
fmt.Println(strings.Index("chicken", "dmr"))

Output:

4
-1

func IndexAny Uses

❖
func IndexAny(s, chars string) int

IndexAny returns the index of the first instance of any Unicode code point from chars in s, or -1 if no Unicode code point from chars is present in s.

Example

Code:play  

fmt.Println(strings.IndexAny("chicken", "aeiouy"))
fmt.Println(strings.IndexAny("crwth", "aeiouy"))

Output:

2
-1

func IndexByte Uses

❖
func IndexByte(s string, c byte) int

IndexByte returns the index of the first instance of c in s, or -1 if c is not present in s.

Example

Code:play  

fmt.Println(strings.IndexByte("golang", 'g'))
fmt.Println(strings.IndexByte("gophers", 'h'))
fmt.Println(strings.IndexByte("golang", 'x'))

Output:

0
3
-1

func IndexFunc Uses

❖
func IndexFunc(s string, f func(rune) bool) int

IndexFunc returns the index into s of the first Unicode code point satisfying f(c), or -1 if none do.

Example

Code:play  

f := func(c rune) bool {
    return unicode.Is(unicode.Han, c)
}
fmt.Println(strings.IndexFunc("Hello, 世界", f))
fmt.Println(strings.IndexFunc("Hello, world", f))

Output:

7
-1

func IndexRune Uses

❖
func IndexRune(s string, r rune) int

IndexRune returns the index of the first instance of the Unicode code point r, or -1 if rune is not present in s. If r is utf8.RuneError, it returns the first instance of any invalid UTF-8 byte sequence.

Example

Code:play  

fmt.Println(strings.IndexRune("chicken", 'k'))
fmt.Println(strings.IndexRune("chicken", 'd'))

Output:

4
-1

func Join Uses

❖
func Join(a []string, sep string) string

Join concatenates the elements of a to create a single string. The separator string sep is placed between elements in the resulting string.

Example

Code:play  

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

Output:

foo, bar, baz

func LastIndex Uses

❖
func LastIndex(s, substr string) int

LastIndex returns the index of the last instance of substr in s, or -1 if substr is not present in s.

Example

Code:play  

fmt.Println(strings.Index("go gopher", "go"))
fmt.Println(strings.LastIndex("go gopher", "go"))
fmt.Println(strings.LastIndex("go gopher", "rodent"))

Output:

0
3
-1

func LastIndexAny Uses

❖
func LastIndexAny(s, chars string) int

LastIndexAny returns the index of the last instance of any Unicode code point from chars in s, or -1 if no Unicode code point from chars is present in s.

Example

Code:play  

fmt.Println(strings.LastIndexAny("go gopher", "go"))
fmt.Println(strings.LastIndexAny("go gopher", "rodent"))
fmt.Println(strings.LastIndexAny("go gopher", "fail"))

Output:

4
8
-1

func LastIndexByte Uses

❖
func LastIndexByte(s string, c byte) int

LastIndexByte returns the index of the last instance of c in s, or -1 if c is not present in s.

Example

Code:play  

fmt.Println(strings.LastIndexByte("Hello, world", 'l'))
fmt.Println(strings.LastIndexByte("Hello, world", 'o'))
fmt.Println(strings.LastIndexByte("Hello, world", 'x'))

Output:

10
8
-1

func LastIndexFunc Uses

❖
func LastIndexFunc(s string, f func(rune) bool) int

LastIndexFunc returns the index into s of the last Unicode code point satisfying f(c), or -1 if none do.

Example

Code:play  

fmt.Println(strings.LastIndexFunc("go 123", unicode.IsNumber))
fmt.Println(strings.LastIndexFunc("123 go", unicode.IsNumber))
fmt.Println(strings.LastIndexFunc("go", unicode.IsNumber))

Output:

5
2
-1

func Map Uses

❖
func Map(mapping func(rune) rune, s string) string

Map returns a copy of the string s with all its characters modified according to the mapping function. If mapping returns a negative value, the character is dropped from the string with no replacement.

Example

Code:play  

rot13 := func(r rune) rune {
    switch {
    case r >= 'A' && r <= 'Z':
        return 'A' + (r-'A'+13)%26
    case r >= 'a' && r <= 'z':
        return 'a' + (r-'a'+13)%26
    }
    return r
}
fmt.Println(strings.Map(rot13, "'Twas brillig and the slithy gopher..."))

Output:

'Gjnf oevyyvt naq gur fyvgul tbcure...

func Repeat Uses

❖
func Repeat(s string, count int) string

Repeat returns a new string consisting of count copies of the string s.

It panics if count is negative or if the result of (len(s) * count) overflows.

Example

Code:play  

fmt.Println("ba" + strings.Repeat("na", 2))

Output:

banana

func Replace Uses

❖
func Replace(s, old, new string, n int) string

Replace returns a copy of the string s with the first n non-overlapping instances of old replaced by new. If old is empty, it matches at the beginning of the string and after each UTF-8 sequence, yielding up to k+1 replacements for a k-rune string. If n < 0, there is no limit on the number of replacements.

Example

Code:play  

fmt.Println(strings.Replace("oink oink oink", "k", "ky", 2))
fmt.Println(strings.Replace("oink oink oink", "oink", "moo", -1))

Output:

oinky oinky oink
moo moo moo

func Split Uses

❖
func Split(s, sep string) []string

Split slices s into all substrings separated by sep and returns a slice of the substrings between those separators.

If s does not contain sep and sep is not empty, Split returns a slice of length 1 whose only element is s.

If sep is empty, Split splits after each UTF-8 sequence. If both s and sep are empty, Split returns an empty slice.

It is equivalent to SplitN with a count of -1.

Example

Code:play  

fmt.Printf("%q\n", strings.Split("a,b,c", ","))
fmt.Printf("%q\n", strings.Split("a man a plan a canal panama", "a "))
fmt.Printf("%q\n", strings.Split(" xyz ", ""))
fmt.Printf("%q\n", strings.Split("", "Bernardo O'Higgins"))

Output:

["a" "b" "c"]
["" "man " "plan " "canal panama"]
[" " "x" "y" "z" " "]
[""]

func SplitAfter Uses

❖
func SplitAfter(s, sep string) []string

SplitAfter slices s into all substrings after each instance of sep and returns a slice of those substrings.

If s does not contain sep and sep is not empty, SplitAfter returns a slice of length 1 whose only element is s.

If sep is empty, SplitAfter splits after each UTF-8 sequence. If both s and sep are empty, SplitAfter returns an empty slice.

It is equivalent to SplitAfterN with a count of -1.

Example

Code:play  

fmt.Printf("%q\n", strings.SplitAfter("a,b,c", ","))

Output:

["a," "b," "c"]

func SplitAfterN Uses

❖
func SplitAfterN(s, sep string, n int) []string

SplitAfterN slices s into substrings after each instance of sep and returns a slice of those substrings.

The count determines the number of substrings to return: 

n > 0: at most n substrings; the last substring will be the unsplit remainder.
n == 0: the result is nil (zero substrings)
n < 0: all substrings

Edge cases for s and sep (for example, empty strings) are handled as described in the documentation for SplitAfter.

Example

Code:play  

fmt.Printf("%q\n", strings.SplitAfterN("a,b,c", ",", 2))

Output:

["a," "b,c"]

func SplitN Uses

❖
func SplitN(s, sep string, n int) []string

SplitN slices s into substrings separated by sep and returns a slice of the substrings between those separators.

The count determines the number of substrings to return: 

n > 0: at most n substrings; the last substring will be the unsplit remainder.
n == 0: the result is nil (zero substrings)
n < 0: all substrings

Edge cases for s and sep (for example, empty strings) are handled as described in the documentation for Split.

Example

Code:play  

fmt.Printf("%q\n", strings.SplitN("a,b,c", ",", 2))
z := strings.SplitN("a,b,c", ",", 0)
fmt.Printf("%q (nil = %v)\n", z, z == nil)

Output:

["a" "b,c"]
[] (nil = true)

func Title Uses

❖
func Title(s string) string

Title returns a copy of the string s with all Unicode letters that begin words mapped to their title case.

BUG(rsc): The rule Title uses for word boundaries does not handle Unicode punctuation properly.

Example

Code:play  

fmt.Println(strings.Title("her royal highness"))

Output:

Her Royal Highness

func ToLower Uses

❖
func ToLower(s string) string

ToLower returns a copy of the string s with all Unicode letters mapped to their lower case.

Example

Code:play  

fmt.Println(strings.ToLower("Gopher"))

Output:

gopher

func ToLowerSpecial Uses

❖
func ToLowerSpecial(c unicode.SpecialCase, s string) string

ToLowerSpecial returns a copy of the string s with all Unicode letters mapped to their lower case, giving priority to the special casing rules.

Example

Code:play  

fmt.Println(strings.ToLowerSpecial(unicode.TurkishCase, "Önnek İş"))

Output:

önnek iş

func ToTitle Uses

❖
func ToTitle(s string) string

ToTitle returns a copy of the string s with all Unicode letters mapped to their title case.

Example

Code:play  

fmt.Println(strings.ToTitle("loud noises"))
fmt.Println(strings.ToTitle("хлеб"))

Output:

LOUD NOISES
ХЛЕБ

func ToTitleSpecial Uses

❖
func ToTitleSpecial(c unicode.SpecialCase, s string) string

ToTitleSpecial returns a copy of the string s with all Unicode letters mapped to their title case, giving priority to the special casing rules.

Example

Code:play  

fmt.Println(strings.ToTitleSpecial(unicode.TurkishCase, "dünyanın ilk borsa yapısı Aizonai kabul edilir"))

Output:

DÜNYANIN İLK BORSA YAPISI AİZONAİ KABUL EDİLİR

func ToUpper Uses

❖
func ToUpper(s string) string

ToUpper returns a copy of the string s with all Unicode letters mapped to their upper case.

Example

Code:play  

fmt.Println(strings.ToUpper("Gopher"))

Output:

GOPHER

func ToUpperSpecial Uses

❖
func ToUpperSpecial(c unicode.SpecialCase, s string) string

ToUpperSpecial returns a copy of the string s with all Unicode letters mapped to their upper case, giving priority to the special casing rules.

Example

Code:play  

fmt.Println(strings.ToUpperSpecial(unicode.TurkishCase, "örnek iş"))

Output:

ÖRNEK İŞ

func Trim Uses

❖
func Trim(s string, cutset string) string

Trim returns a slice of the string s with all leading and trailing Unicode code points contained in cutset removed.

Example

Code:play  

fmt.Print(strings.Trim("¡¡¡Hello, Gophers!!!", "!¡"))

Output:

Hello, Gophers

func TrimFunc Uses

❖
func TrimFunc(s string, f func(rune) bool) string

TrimFunc returns a slice of the string s with all leading and trailing Unicode code points c satisfying f(c) removed.

Example

Code:play  

fmt.Print(strings.TrimFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
    return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))

Output:

Hello, Gophers

func TrimLeft Uses

❖
func TrimLeft(s string, cutset string) string

TrimLeft returns a slice of the string s with all leading Unicode code points contained in cutset removed.

To remove a prefix, use TrimPrefix instead.

Example

Code:play  

fmt.Print(strings.TrimLeft("¡¡¡Hello, Gophers!!!", "!¡"))

Output:

Hello, Gophers!!!

func TrimLeftFunc Uses

❖
func TrimLeftFunc(s string, f func(rune) bool) string

TrimLeftFunc returns a slice of the string s with all leading Unicode code points c satisfying f(c) removed.

Example

Code:play  

fmt.Print(strings.TrimLeftFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
    return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))

Output:

Hello, Gophers!!!

func TrimPrefix Uses

❖
func TrimPrefix(s, prefix string) string

TrimPrefix returns s without the provided leading prefix string. If s doesn't start with prefix, s is returned unchanged.

Example

Code:play  

var s = "¡¡¡Hello, Gophers!!!"
s = strings.TrimPrefix(s, "¡¡¡Hello, ")
s = strings.TrimPrefix(s, "¡¡¡Howdy, ")
fmt.Print(s)

Output:

Gophers!!!

func TrimRight Uses

❖
func TrimRight(s string, cutset string) string

TrimRight returns a slice of the string s, with all trailing Unicode code points contained in cutset removed.

To remove a suffix, use TrimSuffix instead.

Example

Code:play  

fmt.Print(strings.TrimRight("¡¡¡Hello, Gophers!!!", "!¡"))

Output:

¡¡¡Hello, Gophers

func TrimRightFunc Uses

❖
func TrimRightFunc(s string, f func(rune) bool) string

TrimRightFunc returns a slice of the string s with all trailing Unicode code points c satisfying f(c) removed.

Example

Code:play  

fmt.Print(strings.TrimRightFunc("¡¡¡Hello, Gophers!!!", func(r rune) bool {
    return !unicode.IsLetter(r) && !unicode.IsNumber(r)
}))

Output:

¡¡¡Hello, Gophers

func TrimSpace Uses

❖
func TrimSpace(s string) string

TrimSpace returns a slice of the string s, with all leading and trailing white space removed, as defined by Unicode.

Example

Code:play  

fmt.Println(strings.TrimSpace(" \t\n Hello, Gophers \n\t\r\n"))

Output:

Hello, Gophers

func TrimSuffix Uses

❖
func TrimSuffix(s, suffix string) string

TrimSuffix returns s without the provided trailing suffix string. If s doesn't end with suffix, s is returned unchanged.

Example

Code:play  

var s = "¡¡¡Hello, Gophers!!!"
s = strings.TrimSuffix(s, ", Gophers!!!")
s = strings.TrimSuffix(s, ", Marmots!!!")
fmt.Print(s)

Output:

¡¡¡Hello

type Builder Uses

❖
type Builder struct {
    // contains filtered or unexported fields
}

A Builder is used to efficiently build a string using Write methods. It minimizes memory copying. The zero value is ready to use. Do not copy a non-zero Builder.

Example

Code:play  

var b strings.Builder
for i := 3; i >= 1; i-- {
    fmt.Fprintf(&b, "%d...", i)
}
b.WriteString("ignition")
fmt.Println(b.String())

Output:

3...2...1...ignition

func (*Builder) Grow Uses

❖
func (b *Builder) Grow(n int)

Grow grows b's capacity, if necessary, to guarantee space for another n bytes. After Grow(n), at least n bytes can be written to b without another allocation. If n is negative, Grow panics.

func (*Builder) Len Uses

❖
func (b *Builder) Len() int

Len returns the number of accumulated bytes; b.Len() == len(b.String()).

func (*Builder) Reset Uses

❖
func (b *Builder) Reset()

Reset resets the Builder to be empty.

func (*Builder) String Uses

❖
func (b *Builder) String() string

String returns the accumulated string.

func (*Builder) Write Uses

❖
func (b *Builder) Write(p []byte) (int, error)

Write appends the contents of p to b's buffer. Write always returns len(p), nil.

func (*Builder) WriteByte Uses

❖
func (b *Builder) WriteByte(c byte) error

WriteByte appends the byte c to b's buffer. The returned error is always nil.

func (*Builder) WriteRune Uses

❖
func (b *Builder) WriteRune(r rune) (int, error)

WriteRune appends the UTF-8 encoding of Unicode code point r to b's buffer. It returns the length of r and a nil error.

func (*Builder) WriteString Uses

❖
func (b *Builder) WriteString(s string) (int, error)

WriteString appends the contents of s to b's buffer. It returns the length of s and a nil error.

type Reader Uses

❖
type Reader struct {
    // contains filtered or unexported fields
}

A Reader implements the io.Reader, io.ReaderAt, io.Seeker, io.WriterTo, io.ByteScanner, and io.RuneScanner interfaces by reading from a string.

func NewReader Uses

❖
func NewReader(s string) *Reader

NewReader returns a new Reader reading from s. It is similar to bytes.NewBufferString but more efficient and read-only.

func (*Reader) Len Uses

❖
func (r *Reader) Len() int

Len returns the number of bytes of the unread portion of the string.

func (*Reader) Read Uses

❖
func (r *Reader) Read(b []byte) (n int, err error)

func (*Reader) ReadAt Uses

❖
func (r *Reader) ReadAt(b []byte, off int64) (n int, err error)

func (*Reader) ReadByte Uses

❖
func (r *Reader) ReadByte() (byte, error)

func (*Reader) ReadRune Uses

❖
func (r *Reader) ReadRune() (ch rune, size int, err error)

func (*Reader) Reset Uses

❖
func (r *Reader) Reset(s string)

Reset resets the Reader to be reading from s.

func (*Reader) Seek Uses

❖
func (r *Reader) Seek(offset int64, whence int) (int64, error)

Seek implements the io.Seeker interface.

func (*Reader) Size Uses

❖
func (r *Reader) Size() int64

Size returns the original length of the underlying string. Size is the number of bytes available for reading via ReadAt. The returned value is always the same and is not affected by calls to any other method.

func (*Reader) UnreadByte Uses

❖
func (r *Reader) UnreadByte() error

func (*Reader) UnreadRune Uses

❖
func (r *Reader) UnreadRune() error

func (*Reader) WriteTo Uses

❖
func (r *Reader) WriteTo(w io.Writer) (n int64, err error)

WriteTo implements the io.WriterTo interface.

type Replacer Uses

❖
type Replacer struct {
    // contains filtered or unexported fields
}

Replacer replaces a list of strings with replacements. It is safe for concurrent use by multiple goroutines.

func NewReplacer Uses

❖
func NewReplacer(oldnew ...string) *Replacer

NewReplacer returns a new Replacer from a list of old, new string pairs. Replacements are performed in the order they appear in the target string, without overlapping matches.

Example

Code:play  

r := strings.NewReplacer("<", "&lt;", ">", "&gt;")
fmt.Println(r.Replace("This is <b>HTML</b>!"))

Output:

This is &lt;b&gt;HTML&lt;/b&gt;!

func (*Replacer) Replace Uses

❖
func (r *Replacer) Replace(s string) string

Replace returns a copy of s with all replacements performed.

func (*Replacer) WriteString Uses

❖
func (r *Replacer) WriteString(w io.Writer, s string) (n int, err error)

WriteString writes s to w with all replacements performed.

Bugs

☞ The rule Title uses for word boundaries does not handle Unicode punctuation properly.

Package strings imports 6 packages (graph) and is imported by 298321 packages. Updated 2018-10-03. Refresh now. Tools for package owners.