不使用Sprintf实现Stringer接口的方法

huangapple
go评论108阅读模式
英文:

Stringer implementation without using Sprintf

问题

我正在通过golang教程进行学习，但在其中一个练习中遇到了问题。我不确定为什么以下的String()函数不起作用：

  1. type IPAddr [4]byte
  3. func (addr IPAddr) String() string {
  4.     return string(addr[0]) + "." + string(addr[1]) + "." + string(addr[2]) + "." + string(addr[3])
  5. }
  7. func main() {
  8.     addrs := map[string]IPAddr{
  9.         "loopback":  {127, 0, 0, 1},
  10.         "googleDNS": {8, 8, 8, 8},
  11.     }
  12.     for n, a := range addrs {
  13.         fmt.Printf("%v: %v\n", n, a)
  14.     }
  15. }

输出结果为：

  1. loopback: ...
  2. googleDNS: ...

虽然使用fmt.Sprintf()可能是一个更好的解决方案，但我不确定为什么这个函数不起作用。

英文:

I am working through the golang tour and I am stuck in one of the exercises. I am not sure why the following does not work for a String() function:

  1. type IPAddr [4]byte
  3. func (addr IPAddr) String() string {
  4. 	return string(addr[0]) + "." + string(addr[1]) + "." + string(addr[2]) + "." + string(addr[3])
  5. }
  7. func main() {
  8. 	addrs := map[string]IPAddr{
  9. 		"loopback":  {127, 0, 0, 1},
  10. 		"googleDNS": {8, 8, 8, 8},
  11. 	}
  12. 	for n, a := range addrs {
  13. 		fmt.Printf("%v: %v\n", n, a)
  14. 	}
  15. }

Output:

  1. loopback: ...
  2. googleDNS: ...

Granted that using fmt.Sprintf() would be a nicer solution, but I'm not sure I understand why that function doesn't work.

答案1

得分: 7

这里发生的情况是，你直接将字节（例如127）传递给字符串，并期望它在转换为字符串之前将该字节表示为整数127。但实际上，它将其解释为具有字节值127的字符。

相反，你应该将该字节值转换为整数，然后使用strconv库将其格式化为字符串。

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"strconv"
  6. )
  8. type IPAddr [4]byte
  10. func (addr IPAddr) String() string {
  11.     return strconv.Itoa(int(addr[0])) + "." + strconv.Itoa(int(addr[1])) + "." + strconv.Itoa(int(addr[2])) + "." + strconv.Itoa(int(addr[3]))
  12. }
  14. func main() {
  15.     addrs := map[string]IPAddr{
  16.         "loopback":  {127, 0, 0, 1},
  17.         "googleDNS": {8, 8, 8, 8},
  18.     }
  19.     for n, a := range addrs {
  20.         fmt.Printf("%v: %v\n", n, a)
  21.     }
  22. }

输出：

  1. loopback: 127.0.0.1
  2. googleDNS: 8.8.8.8
英文:

What's happening there is that you're passing the byte e.g. 127 directly into string and expecting it to represent that byte as the integer 127 before converting it into a string. Instead what it's doing is interpreting it as a character with the byte value 127.

Instead you should convert that byte value into an integer, then use the strconv library to format it as a string.

  1. package main
  3. import (
  4. 	"fmt"
  5. 	"strconv"
  6. )
  8. type IPAddr [4]byte
  10. func (addr IPAddr) String() string {
  11.     return strconv.Itoa(int(addr[0])) + "." + strconv.Itoa(int(addr[1])) + "." + strconv.Itoa(int(addr[2])) + "." + strconv.Itoa(int(addr[3]))
  12. }
  14. func main() {
  15.     addrs := map[string]IPAddr{
  16.         "loopback":  {127, 0, 0, 1},
  17.         "googleDNS": {8, 8, 8, 8},
  18.     }
  19.     for n, a := range addrs {
  20.         fmt.Printf("%v: %v\n", n, a)
  21.     }
  22. }

Output:

  1. loopback: 127.0.0.1
  2. googleDNS: 8.8.8.8

答案2

得分: 0

一个更高效的实现，减少了临时内存分配：

  1. func (addr IPAddr) String() string {
  2.     buf := make([]byte, 0, 3+1+3+1+3+1+3)
  3.     return string(
  4.         strconv.AppendInt(
  5.             append(
  6.                 strconv.AppendInt(
  7.                     append(
  8.                         strconv.AppendInt(
  9.                             append(
  10.                                 strconv.AppendInt(buf,
  11.                                     int64(addr[0]), 10), '.'), 
  12.                             int64(addr[1]), 10), '.'),
  13.                     int64(addr[2]), 10), '.'),
  14.             int64(addr[3]), 10))
  15. }
英文:

A more efficient implementation with less temporary memory allocations:

  1. func (addr IPAddr) String() string {
  2. 	buf := make([]byte, 0, 3+1+3+1+3+1+3)
  3. 	return string(
  4. 		strconv.AppendInt(
  5. 			append(
  6. 				strconv.AppendInt(
  7. 					append(
  8. 						strconv.AppendInt(
  9. 							append(
  10. 								strconv.AppendInt(buf,
  11. 									int64(addr[0]), 10), '.'),
  12. 							int64(addr[1]), 10), '.'),
  13. 					int64(addr[2]), 10), '.'),
  14. 			int64(addr[3]), 10))
  15. }

huangapple
  • 本文由 发表于 2015年4月14日 04:55:42
  • 转载请务必保留本文链接：https://go.coder-hub.com/29614943.html
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