// string is the set of all strings of 8-bit bytes, conventionally but not
// necessarily representing UTF-8-encoded text. A string may be empty, but
// not nil. Values of string type are immutable.

s := "Hello, 世界"
fmt.Println(len(s)) // 13
fmt.Println([]byte(s)) // [72 101 108 108 111 44 32 228 184 150 231 149 140]

- bytes.Count() 
- strings.Count() 
- 將字符串轉(zhuǎn)換為 []runee 后調(diào)用 len 函數(shù)
- 使用 utf8.RuneCountInString() 

package main
import (
  "bytes"
  "fmt"
  "strings"
  "testing"
  "unicode/utf8"
)
/*
在 golang 中不能直接用 len 函數(shù)來(lái)統(tǒng)計(jì)字符串長(zhǎng)度，查看了下源碼發(fā)現(xiàn)字符串是以 UTF-8 為格式存儲(chǔ)的，說(shuō)明 len 函數(shù)是取得包含 byte 的個(gè)數(shù)
*/
func main() {
  s := "hello, 世界"
  fmt.Println(len(s))  // 13
  fmt.Println([]byte(s)) // [72 101 108 108 111 44 32 228 184 150 231 149 140]
  fmt.Print(f1(s))
}
func f1(s string) int {
  return bytes.Count([]byte(s), nil) - 1
}
func f2(s string) int {
  return strings.Count(s, "") - 1
}
func f3(s string) int {
  return len([]rune(s))
}
func f4(s string) int {
  return utf8.RuneCountInString(s)
}
var s = "Hello, 世界"
func Benchmark1(b *testing.B) {
  for i := 0; i < b.N; i++ {
    f1(s)
  }
}
func Benchmark2(b *testing.B) {
  for i := 0; i < b.N; i++ {
    f2(s)
  }
}
func Benchmark3(b *testing.B) {
  for i := 0; i < b.N; i++ {
    f3(s)
  }
}
func Benchmark4(b *testing.B) {
  for i := 0; i < b.N; i++ {
    f4(s)
  }
}