dongwan0574 2019-08-18 02:21
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日期输出从json.Encoder哪里来?

At the end of the JSON and Go blog post you'll find this sample program:

package main

import (
    "encoding/json"
    "log"
    "os"
)

func main() {
    dec := json.NewDecoder(os.Stdin)
    enc := json.NewEncoder(os.Stdout)
    for {
        var v map[string]interface{}
        if err := dec.Decode(&v); err != nil {
            log.Println(err)
            return
        }
        for k := range v {
            if k != "Name" {
                delete(v, k)
            }
        }
        if err := enc.Encode(&v); err != nil {
            log.Println(err)
        }
    }
}

I compiled this with go build json_decoder.go and then ran the program like so in bash:

echo '{"Name":"Wednesday","Age":6,"Parents":["Gomez","Morticia"]}' | json_decoder

and received this output:

{"Name":"Wednesday"}
2019/08/17 22:09:20 EOF

The first line of output is exactly what I'd expect. But where is the line 2019/08/17 22:09:20 EOF coming from?

  • 写回答

2条回答 默认 最新

  • douhuai2861 2019-08-18 02:48
    关注

    When EOF is reached the decoder returns io.EOF which is then is being output by the logger log.Println(err) with a timestamp prepended.

    You can check for EOF when decoding like this for example

    if err := dec.Decode(&v); err != nil {
        if err != io.EOF {
            log.Println(err)
        }
        return
    }
    

    Output:

    ➜ echo '{"Name":"Wednesday","Age":6,"Parents":["Gomez","Morticia"]}' | ./json_decoder
    {"Name":"Wednesday"}
    
    本回答被题主选为最佳回答 , 对您是否有帮助呢?
    评论
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