go version go1.10.3

Go中的字符串用法，可以在 godoc.org 上查看语法和用法。

最简单的语法就是获取字符串中的子串

s := "hello world"

fmt.Println(s[1:3], s[0:])

一：查找

1、查找返回索引

godoc.org上索引的方法

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.
说明：返回子串substr在字符串s中第一次出现的位置
如果找不到则返回-1；如果substr为空，则返回0

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "hello h 世界!"

    fmt.Println(strings.Index(s, "h"))
    fmt.Println(strings.Index(s, "!"))
    fmt.Println(strings.Index(s, "wo"))
}

//output:
//0
//14
//-1

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.
说明：返回字符串 chars 中的任一个字符在字符串 s 中第一次出现的位置
如果找不到，则返回 -1，如果 chars 为空，则返回 -1

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "hello h golang 世界! GO GO GO"

    fmt.Println(strings.IndexAny(s, "bbc"))
    fmt.Println(strings.IndexAny(s, "elly")) //e这个字符出现在了第1个索引位置
    fmt.Println(strings.IndexAny(s, "dof")) //d没有出现在字符中，o出现在第4个索引位置，也就是说dof按字符顺序依次检查
}
//output
//-1   
//1
//4

LastIndex

func LastIndex(s, substr string) int

说明：返回字符串substr在s中最后一次出现的位置
如果找不到，则返回 -1，如果 sep 为空，则返回字符串的长度
例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "hello h golang 世界! GO GO GO"

    fmt.Println(strings.LastIndex(s, "o")) //从后面输出的结构看，查找区分大小写
    fmt.Println(strings.LastIndex(s, "G")) //从后面输出的结构看，查找区分大小写
    fmt.Println(strings.LastIndex(s, "go"))
}
//output:
//9
//29
//8

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.
说明：返回字符串 r 在字符串 s 中第一次出现的位置
如果找不到，则返回 -1

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "hello h golang 世界! GO GO GO"

    fmt.Println(strings.IndexRune(s, '\n'))
    fmt.Println(strings.IndexRune(s, '界'))
    fmt.Println(strings.IndexRune(s, 0))
}
//output:
//-1
//18
//-1

2、是否包含

Contains

func Contains(s, substr string) bool

Contains reports whether substr is within s.
说明：s 是否包含 substr 字符串，返回true 或 false

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    a := "hello"
    b := "el"
    c := "world"

    fmt.Println(strings.Contains(a, b))
    fmt.Println(strings.Contains(a, c))
}
//output:
//true
//false

ContainsAny

func ContainsAny(s, chars string) bool

ContainsAny reports whether any Unicode code points in chars are within s.
说明：在 s 中是否包含 chars 中任一字符，如果是返回 true，不是返回 false

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    a = "hello"
    b = "e & o"
    c = "ebe"
    fmt.Println(strings.ContainsAny(a, b))
    fmt.Println(strings.ContainsAny(a, c)) //e, b, e 是否在 "hello" 中
}
//output:
//true
//true

ContainsRune

func ContainsRune(s string, r rune) bool

说明：判断字符串 s 中是否包含字符 r

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    a := "hello"
    b := "el"
    c := "world"

    fmt.Println(strings.Contains(a, b))
    fmt.Println(strings.Contains(a, c))

    a = "hello"
    b = "e & o"
    c = "ebe"
    fmt.Println(strings.ContainsAny(a, b))
    fmt.Println(strings.ContainsAny(a, c))

    fmt.Println("======contains rune=======")
    s := "Hello,世界!"
    fmt.Println(strings.ContainsRune(s, 2))         // false
    fmt.Println(strings.ContainsRune(s, rune('e'))) // true
    fmt.Println(strings.ContainsRune(s, 'e'))       // true
    fmt.Println(strings.ContainsRune(s, '界'))       //true
}
//output:
//false
//true
//true
//true

3、查找前缀后缀

HasPrefix

func HasPrefix(s, prefix string) bool

说明：s 的前缀是否包含 prefix 字符

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    fmt.Println(strings.HasPrefix("hello", "lo")) //false
    fmt.Println(strings.HasPrefix("hello", "O"))  //false
    fmt.Println(strings.HasPrefix("Hello", "hel")) // false, 区分大小写
    fmt.Println(strings.HasPrefix("Hello", "Hel")) //true
}
//output:
//false
//false
//false
//true

HasSuffix

func HasSuffix(s, suffix string) bool

说明：跟上面的函数 HasPrefix 相反， s 字符串后缀中是否包含 suffix 字符

4、计数

Count

https://godoc.org/strings#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.
说明：如果substr存在s中，那么返回多少个；如果substr 为空字符串，那么返回 s 的长度 + 1

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    fmt.Println("========Count========")
    s := "Banana"
    fmt.Println(strings.Count(s, "ban")) //result：0
    fmt.Println(strings.Count(s, "ana")) //result：1
    fmt.Println(strings.Count(s, ""))    //result：7
}

二：比较

compare

godoc.org的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.
说明：a，b 2个字符串比较，如果相等，返回 0；如果 a < b，返回 -1；如果 a > b，返回 1；
区分大小写的比较

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    a := "hello"
    b := "hello"
    c := "world"
    d := "llo"
    e := "Hello"

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

    fmt.Println(strings.Compare(a, d))
    fmt.Println(strings.Compare(d, a))

    fmt.Println(strings.Compare(a, e)) //结果为1 不相等，说明compare会区分大小写
}

//output:
//0
//-1
//-1
//1    
//1

EqualFold

func EqualFold(s, t string) bool

EqualFold reports whether s and t, interpreted as UTF-8 strings, are equal under Unicode case-folding.
说明：UTF-8字符串比较的话，不区分大小写

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    a := "hello"
    e := "Hello"

    fmt.Println(strings.EqualFold(a, e))
}
//output:
//true

三：字符变大小写

ToLower

func ToLower(s string) string

说明：把字符串 s 变成大写

例子1：

fmt.Println(strings.ToLower("Hello World")) //hello world

ToUpper

func ToUpper(s string) string

说明：把字符串 s 变大写

例子1：

fmt.Println(strings.ToUpper("Hello World")) //HELLO WORLD

ToTitle

func ToTitle(s string) string

说明：把字符串 s 变大写

例子1：

fmt.Println(strings.ToTitle("He llo"))  //HE LLO

Title

https://godoc.org/strings#Title

func Title(s string) string

说明：把首字母变大写

例子1:

fmt.Println(strings.Title("hello world"))  //Hello World

其他一些函数

用一些规则把字符变成大小写

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

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

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

例子1：

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

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

四：替换过滤

Replace

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

说明：将字符串 s 中的 old 字符串替换为 new 字符串，n 表示替换次数，如果 n=-1，全部替换；如果 old 为空，则每个字符都插入一个 new 字符

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "Hello World "

    fmt.Println(strings.Replace(s, " ", ",", -1)) //result: Hello,World,
    fmt.Println(strings.Replace(s, " ", ",", 1))  //result: Hello,World
}

Trim

func Trim(s string, cutset string) string

说明：删除字符串 s 首尾连续包含 cutset 的字符

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "Hello World, HDHe"
  
    fmt.Println(strings.Trim(s, "He")) //llo World, HD
}

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.

例子1：

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

TrimPrefix TrimSuffix

func TrimPrefix(s, prefix string) string

func TrimSuffix(s, suffix string) string

说明：从第一个字符开始，过滤掉左边的字符
过滤掉右边的字符

例子1：

fmt.Println(strings.TrimPrefix("Hello World, He", "He")) //llo World, He
fmt.Println(strings.TrimPrefix("Hello World, He", "el")) //Hello World, He

fmt.Println(strings.TrimSuffix("Hello World, He", "H"))  //Hello World, He
fmt.Println(strings.TrimSuffix("Hello World, He", "He")) //Hello World,

其他一些过滤

func TrimLeft(s string, cutset string) string

func TrimRight(s string, cutset string) string

说明：从左边开始过滤，cutset有连续的字符在 s 中，都过滤掉
从右边开始过滤

例子1：

fmt.Println(strings.TrimLeft("¡¡¡Hello, Gophers!!!", "!¡Ho")) //ello, Gophers!!!
fmt.Println(strings.TrimLeft("¡¡¡Hello, Gophers!!!", "!¡e"))  //Hello, Gophers!!!
fmt.Println(strings.TrimLeft("¡¡¡Hello, Gophers!!!", "!el"))  //¡¡¡Hello, Gophers!!!

带有处理方法的函数：

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

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

说明：用函数来处理字符

例子1：

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

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

五：分割和连接

Split SplitAfter

func Split(s, sep string) []string       //按照 sep 进行分割

func SplitAfter(s, sep string) []string  //把分割字符 sep 也带上

例子1:

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "Hello World, HDHe, gopher!"
    fmt.Printf("%q\n", strings.Split(s, ",")) //["Hello World" " HDHe" " gopher!"]

    fmt.Printf("%q\n", strings.Split("o Hello World, gopher", "o "))
    //output: ["" "Hell" "World, gopher"]

    fmt.Printf("%q\n", strings.Split("Hello World", ""))
    //["H" "e" "l" "l" "o" " " "W" "o" "r" "l" "d"]
}

例子2：

package main

import (
    "fmt"
    "strings"
)

func main() {
    fmt.Printf("%q\n", strings.SplitAfter("Hello, World, Go", ",")) 
  //["Hello," " World," " Go"]
}

SplitN SplitAfterN

func SplitN(s, sep string, n int) []string         //根据分隔符来分割字符串，n 表示分成多少份

func SplitAfterN(s, sep string, n int) []string   //把分隔符sep也带上，n 表示分成多少份

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    fmt.Printf("%q\n", strings.SplitN("Hello, World, Go, He", ",", 2))      //["Hello" " World, Go, He"]
    fmt.Printf("%q\n", strings.SplitAfterN("Hello, World, Go, He", ",", 2)) //["Hello," " World, Go, He"]
    fmt.Printf("%q\n", strings.SplitAfterN("Hello, World, Go, He", ",", 3)) //["Hello," " World," " Go, He"]
}

Join

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

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    fmt.Println(strings.Join([]string{"hello", "world"}, ", ")) //hello, world
}

六：字符读写

Builder

结构体

// 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.
type Builder struct {
    addr *Builder // of receiver, to detect copies by value
    buf  []byte
}

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.
这个结构能使写字符时候更加高效，使用更小的内存

在Go 1.10以前我们hi怎么做的呢？

package main

import (
    "bytes"
    "fmt"
)

func main() {
    //以前我们这样来做
    fmt.Println("=====bytesbuffer====")
    var buf bytes.Buffer
    for i, p := range []int{2, 3, 5, 7, 11, 13} {
        fmt.Fprintf(&buf, "%d:%d, ", i+1, p)
    }
    buf.Truncate(buf.Len() - 2) // Remove trailing ", "
    s := buf.String()           // Copy into a new string
    fmt.Println(s)


    /**
      output:
      =====bytesbuffer====
      1:2, 2:3, 3:5, 4:7, 5:11, 6:13
      **/
}

现在我们可以用builder了

package main

import (
    "bytes"
    "fmt"
    "strings"
)

func main() {
    fmt.Println("=======Builder=======")
    //现在我们可以这样做
    var b strings.Builder
    b.Grow(32)
    for i, p := range []int{2, 3, 5, 7, 11, 13} {
        fmt.Fprintf(&b, "%d:%d, ", i+1, p)
    }
    s := b.String()   // no copying
    s = s[:b.Len()-2] // no copying (removes trailing ", ")
    fmt.Println(s)

    /**
      output:
      =======Builder=======
      1:2, 2:3, 3:5, 4:7, 5:11, 6:13
      **/
}

Reader

结构体

// A Reader implements the io.Reader, io.ReaderAt, io.Seeker, io.WriterTo,
// io.ByteScanner, and io.RuneScanner interfaces by reading
// from a string.
// The zero value for Reader operates like a Reader of an empty string.
type Reader struct {
    s        string
    i        int64 // current reading index
    prevRune int   // index of previous rune; or < 0
}

// Reader 结构通过读取字符串，实现了 io.Reader，io.ReaderAt，
// io.Seeker，io.WriterTo，io.ByteScanner，io.RuneScanner 接口

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

// 通过字符串 s 创建 strings.Reader 对象
// 这个函数类似于 bytes.NewBufferString
// 但比 bytes.NewBufferString 更有效率，而且只读
func NewReader(s string) *Reader { return &Reader{s, 0, -1} }

计算长度 Len

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "Hello, World"
    r := strings.NewReader(s)

    fmt.Println(r.Len()) //12
}

读取数据

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

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

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

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

例子1：

package main

import (
    "fmt"
    "strings"
)

func main() {
    s := "Hello, World"
    r := strings.NewReader(s)

    fmt.Println(r.Len()) //12

    b := make([]byte, 5)
    for n, _ := r.Read(b); n > 0; n, _ = r.Read(b) {
        fmt.Printf("%q, ", b[:n])
    }
    //"Hello", ", Wor", "ld",

    fmt.Println("======ReadAt========")

    r = strings.NewReader(s) //创建reader
    b = make([]byte, 5)      //创建长度为 5 个字节的缓冲区
    n, _ := r.ReadAt(b, 0)
    fmt.Printf("%q\n", b[:n]) //"Hello"

    n, _ = r.ReadAt(b, 7)
    fmt.Printf("%q\n", b[:n]) //"World"

    // 读取 r 中的一个字节
    for i := 0; i < 3; i++ {
        b, _ := r.ReadByte()
        fmt.Printf("%q, ", b) // 'H', 'e', 'l',
    }

}

参考：

https://godoc.org/strings
https://yourbasic.org/golang/string-functions-reference-cheat-sheet/
https://www.cnblogs.com/golove/p/3236300.html

Go package(2) strings 用法

一：查找

1、查找返回索引

Index

IndexAny

LastIndex

IndexRune

2、是否包含

Contains

ContainsAny

ContainsRune

3、查找前缀后缀

HasPrefix

HasSuffix

4、计数

Count

二：比较

compare

EqualFold

三：字符变大小写

ToLower

ToUpper

ToTitle

Title

其他一些函数

四：替换过滤

Replace

Trim

TrimSpace

TrimPrefix TrimSuffix

其他一些过滤

五：分割和连接

Split SplitAfter

SplitN SplitAfterN

Join

六：字符读写

Builder

Reader

参考：

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