Go package(2) strings 用法

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

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