在Go语言中打印JSON文件中的值。

huangapple
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英文:

Print value from JSON file in Go

问题

我正在使用Go语言制作一个货币转换器，它会下载一个JSON文件，然后读取它以打印当前的货币汇率。我不明白如何打印值，我知道我需要使用Unmarshal，但我不明白如何使用它。

例如，我想从JSON文件中打印值1.4075。

这是JSON文件（从这里获取）：

  1. {"base":"GBP","date":"2016-04-08","rates":{"USD":1.4075}}

以下是我目前完成的部分。

  1. package main
  3. import(
  4.   "encoding/json"
  5.   "fmt"
  6.   "io/ioutil"
  7. )
  9. func main(){
  10.   fromCurrency:="GBP"
  11.   toCurrency:="USD"
  12.   
  13.   out, err := os.Create("latest.json")
  14.   if err != nil{
  15.       fmt.Println("Error:", err)
  16.   }
  17.   defer out.Close()
  18.   resp, err := http.Get("http://api.fixer.io/latest?base=" + fromCurrency + "&symbols=" + toCurrency)
  19.   defer resp.Body.Close()
  20.   _, err = io.Copy(out, resp.Body)
  21.   if err!= nil{
  22.       fmt.Println("Error:", err)
  23.   }
  24. }
英文:

I am making a currency converter in Go which downloads a JSON file and it then reads it to print the current currency rate. I am unable to understand how to print the value, I know I have to use Unmarshal but I don't understand how to use it.

For example I want to print the value 1.4075 from the JSON file.

Here is the JSON file (This is pulled from here):

  1. {"base":"GBP","date":"2016-04-08","rates":{"USD":1.4075}}

Here is what I have done so far.

  1. package main
  3. import(
  4.   "encoding/json"
  5.   "fmt"
  6.   "io/ioutil"
  7. )
  9. func main(){
  10.   fromCurrency:="GBP"
  11.   toCurrency:="USD"
  12.   
  13.   out, err := os.Create("latest.json")
  14.   if err != nil{
  15.       fmt.Println("Error:", err)
  16.   }
  17.   defer out.Close()
  18.   resp, err := http.Get("http://api.fixer.io/latest?base=" +	fromCurrency + "&symbols=" + toCurrency)
  19.   defer resp.Body.Close()
  20.   _, err = io.Copy(out, resp.Body)
  21.   if err!= nil{
  22.       fmt.Println("Error:", err)
  23.   }
  24. }

答案1

得分: 2

将响应解码为与响应形状匹配的类型。例如：

  1. var data struct {
  2.     Base  string
  3.     Date  string
  4.     Rates map[string]float64
  5. }
  6. if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
  7.     log.Fatal(err)
  8. }

打印相应的值：

  1. if r, ok := data.Rates["USD"]; ok {
  2.     log.Println("Rate", r)
  3. } else {
  4.     log.Println("no rate")
  5. }

完整示例：点击这里

英文:

Decode the response to a type that matches the shape of the response. For example:

  1. var data struct {
  2. 	Base  string
  3. 	Date  string
  4. 	Rates map[string]float64
  5. }
  6. if err := json.NewDecoder(resp.Body).Decode(&data); err != nil {
  7. 	log.Fatal(err)
  8. }

Print the the appropriate value:

  1. if r, ok := data.Rates["USD"]; ok {
  2. 	log.Println("Rate", r)
  3. } else {
  4. 	log.Println("no rate")
  5. }

complete example

huangapple
  • 本文由 发表于 2016年4月10日 06:19:39
  • 转载请务必保留本文链接：https://go.coder-hub.com/36523400.html
  • go
  • json
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