strings

package
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 Go to latest Published: Feb 7, 2020 License: BSD-3-Clause Imports: 5 Imported by: 0

Documentation

Overview

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

Constants

This section is empty.

Variables

This section is empty.

Functions

func Compare 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.Compare("a", "b"))
	fmt.Println(strings.Compare("a", "a"))
	fmt.Println(strings.Compare("b", "a"))
}

Output:

-1
0
1

func Contains 

func Contains(s, substr string) bool

Contains reports whether substr is within s.

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

func ContainsAny(s, chars string) bool

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

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

func ContainsRune(s string, r rune) bool

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

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	// 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 

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 
package main

import (
	"fmt"
	"strings"
)

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

Output:

3
5

func EqualFold 

func EqualFold(s, t string) bool

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

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.EqualFold("Go", "go"))
}

Output:

true

func Fields 

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 an array of substrings of s or an empty list if s contains only white space.

Example 
package main

import (
	"fmt"
	"strings"
)

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

Output:

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

func FieldsFunc 

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 
package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	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 

func HasPrefix(s, prefix string) bool

HasPrefix tests whether the string s begins with prefix.

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.HasPrefix("Gopher", "Go"))
	fmt.Println(strings.HasPrefix("Gopher", "C"))
	fmt.Println(strings.HasPrefix("Gopher", ""))
}

Output:

true
false
true

func HasSuffix 

func HasSuffix(s, suffix string) bool

HasSuffix tests whether the string s ends with suffix.

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.Index("chicken", "ken"))
	fmt.Println(strings.Index("chicken", "dmr"))
}

Output:

4
-1

func IndexAny 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.IndexAny("chicken", "aeiouy"))
	fmt.Println(strings.IndexAny("crwth", "aeiouy"))
}

Output:

2
-1

func IndexByte 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.IndexByte("golang", 'g'))
	fmt.Println(strings.IndexByte("gophers", 'h'))
	fmt.Println(strings.IndexByte("golang", 'x'))
}

Output:

0
3
-1

func IndexFunc 

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 
package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	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 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.IndexRune("chicken", 'k'))
	fmt.Println(strings.IndexRune("chicken", 'd'))
}

Output:

4
-1

func Join 

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 
package main

import (
	"fmt"
	"strings"
)

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

Output:

foo, bar, baz

func LastIndex 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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.

func LastIndexFunc 

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.

func Map 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println("ba" + strings.Repeat("na", 2))
}

Output:

banana

func Replace 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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 
package main

import (
	"fmt"
	"strings"
)

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

Output:

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

func SplitAfterN 

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 
package main

import (
	"fmt"
	"strings"
)

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

Output:

["a," "b,c"]

func SplitN 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.Title("her royal highness"))
}

Output:

Her Royal Highness

func ToLower 

func ToLower(s string) string

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

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ToLower("Gopher"))
}

Output:

gopher

func ToLowerSpecial 

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.

func ToTitle 

func ToTitle(s string) string

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

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ToTitle("loud noises"))
	fmt.Println(strings.ToTitle("хлеб"))
}

Output:

LOUD NOISES
ХЛЕБ

func ToTitleSpecial 

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.

func ToUpper 

func ToUpper(s string) string

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

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.ToUpper("Gopher"))
}

Output:

GOPHER

func ToUpperSpecial 

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.

func Trim 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Printf("[%q]", strings.Trim(" !!! Achtung! Achtung! !!! ", "! "))
}

Output:

["Achtung! Achtung"]

func TrimFunc 

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 
package main

import (
	"fmt"
	"strings"
	"unicode"
)

func main() {
	f := func(c rune) bool {
		return !unicode.IsLetter(c) && !unicode.IsNumber(c)
	}
	fmt.Printf("[%q]", strings.TrimFunc("  Achtung1! Achtung2,...", f))
}

Output:

["Achtung1! Achtung2"]

func TrimLeft 

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.

func TrimLeftFunc 

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.

func TrimPrefix 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	var s = "Goodbye,, world!"
	s = strings.TrimPrefix(s, "Goodbye,")
	s = strings.TrimPrefix(s, "Howdy,")
	fmt.Print("Hello" + s)
}

Output:

Hello, world!

func TrimRight 

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.

func TrimRightFunc 

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.

func TrimSpace 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	fmt.Println(strings.TrimSpace(" \t\n a lone gopher \n\t\r\n"))
}

Output:

a lone gopher

func TrimSuffix 

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 
package main

import (
	"fmt"
	"strings"
)

func main() {
	var s = "Hello, goodbye, etc!"
	s = strings.TrimSuffix(s, "goodbye, etc!")
	s = strings.TrimSuffix(s, "planet")
	fmt.Print(s, "world!")
}

Output:

Hello, world!

Types

type Reader 

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 

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 

func (r *Reader) Len() int

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

func (*Reader) Read 

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

func (*Reader) ReadAt 

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

func (*Reader) ReadByte 

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

func (*Reader) ReadRune 

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

func (*Reader) Reset 

func (r *Reader) Reset(s string)

Reset resets the Reader to be reading from s.

func (*Reader) Seek 

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

Seek implements the io.Seeker interface.

func (*Reader) Size 

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 

func (r *Reader) UnreadByte() error

func (*Reader) UnreadRune 

func (r *Reader) UnreadRune() error

func (*Reader) WriteTo 

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

WriteTo implements the io.WriterTo interface.

type Replacer 

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 

func NewReplacer(oldnew ...string) *Replacer

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

Example 
package main

import (
	"fmt"
	"strings"
)

func main() {
	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 

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

Replace returns a copy of s with all replacements performed.

func (*Replacer) WriteString 

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

WriteString writes s to w with all replacements performed.

Notes

Bugs

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

Source Files

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