一个关于json.Marshal 返回值， 使用fmt.Println输出，屏幕输出却不是json格式的问题

1. 将[]map[string]interface{} 使用json.Marshal进行序列化，将返回结果使用fmt.Println 进行输出，数据结果不是json内容。

• demo code：

  jsonStr := `[{"mid":"4686371941518476","begin":"1632887992","image":"https://wx2.sinaimg.cn/mw690/006KoMX5ly1guxcwyj9vnj603c03cjr902.jpg","aid":"6616523296","tags":"1042015:newTagCategory_004|1042015:newAbilityTag_004005|1042015:city_14005176","level":"S","expired":"1632974393","text":"\u963f\u5bcc\u6c57\u7684\u672a\u6765\u5982\u4f55","event_id":"10000040","data_type":"0","source":"operation_hot"}]`
    m := make([]map[string]interface{}, 0)
    err = json.Unmarshal([]byte(str), &m)
    if err != nil {
        panic(err)
    }
    b, err := json.Marshal(m)
    if err != nil {
        panic(err)
    }
    fmt.Println("", string(b))     // 1. 输出结果正确，json内容
    fmt.Println(string(b))         // 2. 输出结果错误，非json内容
  
    // 屏幕输出:
    // 1.[{"aid":"6616523296","begin":"1632887992","data_type":"0","event_id":"10000040","expired":"1632974393","image":"https://wx2.sinaimg.cn/mw690/006KoMX5ly1guxcwyj9vnj603c03cjr902.jpg","level":"S","mid":"4686371941518476","source":"operation_hot","tags":"1042015:newTagCategory_004|1042015:newAbilityTag_004005|1042015:city_14005176","text":"阿富汗的未来如何"}]
     // 2. [{"aid":"6616523296","begin":"1632887992","data_type":"0","event_id":"10000040","expired":"1632974393","image":"https://wx2.sinaimg.cn/mw690/006KoMX5ly1guxcwyj9vnj603c03cjr902.jpg","level":"S","mid":"4686371941518476","source":"operation_hot","tags":"1042015:newTagCategory_004|1042015:newAbilityTag_004005|1042015:city_14005176","text":"阿富汗的未]  -->非json

2. 查看了fmt.Println 输出代码，区别只是在写buf时多写入一个空格，输出却有差异，不太清楚具体原因

func Fprintln(w io.Writer, a ...interface{}) (n int, err error) {
   p := newPrinter()
   p.doPrintln(a)
   n, err = w.Write(p.buf)
   p.free()
   return
}

func (p *pp) doPrintln(a []interface{}) {
    for argNum, arg := range a { 
        //这里只是多写入了一个空格
        if argNum > 0 {
            p.buf.writeByte(' ')
        }
        p.printArg(arg, 'v')
    }
    p.buf.writeByte('\n')
}