了解标准库是一个非常好的学习语言的方法。接下里的一些章节我们将详细研究标准库中的类型，方法，结合实际应用案例进行有趣的编程。

字符串处理是比较基础的库，我们从简单的库开始入门。

本节我们将继续用实例代码研究以下函数的用法。

func Cut(s, sep string) (before, after string, found bool)
func CutPrefix(s, prefix string) (after string, found bool)
func CutSuffix(s, suffix string) (before string, found bool)
func EqualFold(s, t string) bool
func Fields(s string) []string
func FieldsFunc(s string, f func(rune) bool) []string
func HasPrefix(s, prefix string) bool
func HasSuffix(s, suffix string) bool
package main

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

func main() {
    m := "hello this is strings."

    // cut用sep参数分割原字符串，返回3个参数，切割后左边部分，切割后右边部分，是否存在sep，不存在就不切割
    show := func(s, sep string) {
        before, after, found := strings.Cut(s, sep)
        fmt.Printf("Cut(%q, %q) = %q, %q, %v\n", s, sep, before, after, found)
    }
    show(m, "this")
    show(m, "is")
    show(m, "wow")

    // cutprefix用于去掉前缀，如果原字符串以sep开头就去掉这一部分，返回剩余部分，以及是否存在布尔值
    show2 := func(s, sep string) {
        after, found := strings.CutPrefix(s, sep)
        fmt.Printf("CutPrefix(%q, %q) = %q, %v\n", s, sep, after, found)
    }

    show2(m, "hello")
    show2(m, "this")
    show2(m, "wow")

    // cutsuffix用于去掉后缀，如果原字符串以sep结尾就去掉这一部分，返回剩余部分，以及是否存在布尔值
    show3 := func(s, sep string) {
        after, found := strings.CutSuffix(s, sep)
        fmt.Printf("CutSuffix(%q, %q) = %q, %v\n", s, sep, after, found)
    }

    show3(m, "strings")
    show3(m, "strings.")
    show3(m, "wow")

    // equalFold是否在utf8编码下，不区分大小写相等
    fmt.Println("Go equalFold go?", strings.EqualFold("Go", "go"))

    // fields用空白字符分割字符串，包括空格，多个空格，\t,\r,\n
    fmt.Println("Fields are 1: ", strings.Fields("  foo bar  baz   "))
    fmt.Println("Fields are 2: ", strings.Fields("  foo bar\t baz   "))
    fmt.Println("Fields are 3: ", strings.Fields("  foo bar\r\nbaz   "))

    // fieldsFunc根据提供的函数分割字符串，下面的f函数判断当c不是字母也不是数字的时候返回true，也就是在此处分割
    f := func(c rune) bool {
        return !unicode.IsLetter(c) && !unicode.IsNumber(c)
    }
    fmt.Println("Fields are 4: ", strings.FieldsFunc("  foo1;bar2,baz3...", f))

    // hasPrefix, 区分大小写
    fmt.Println(strings.HasPrefix(m, "Hello"))

    // hasSuffix, 区分大小写
    fmt.Println(strings.HasSuffix(m, "strings."))
}

输出：

Cut("hello this is strings.", "this") = "hello ", " is strings.", true
Cut("hello this is strings.", "is") = "hello th", " is strings.", true
Cut("hello this is strings.", "wow") = "hello this is strings.", "", false
CutPrefix("hello this is strings.", "hello") = " this is strings.", true
CutPrefix("hello this is strings.", "this") = "hello this is strings.", false
CutPrefix("hello this is strings.", "wow") = "hello this is strings.", false
CutSuffix("hello this is strings.", "strings") = "hello this is strings.", false
CutSuffix("hello this is strings.", "strings.") = "hello this is ", true
CutSuffix("hello this is strings.", "wow") = "hello this is strings.", false
Go equalFold go? true
Fields are 1:  [foo bar baz]
Fields are 2:  [foo bar baz]
Fields are 3:  [foo bar baz]
Fields are 4:  [foo1 bar2 baz3]
false
false