IO

包含 io 與 ioutil

範例

讀取檔案轉 JSON

package main
import (
	"os"
  "io/ioutil"
	"encoding/json"
)

func main() {
	jsonFile, err := os.Open("conf.json")
	
	if err != nil {
 	 fmt.Println(err)
	}

	defer jsonFile.Close()

	jsonStr, err := ioutil.ReadAll(jsonFile)
  if err != nil {
      log.Fatal(err)
  }
  doc := make(map[string]interface{})
  if err := json.Unmarshal(jsonStr, &doc); err != nil {
      log.Fatal(err)
  }
  fmt.Println(doc)
  fmt.Println(doc["AWS_ID"])
  fmt.Println(doc["AWS_KEY"])
  for k, v := range doc {
  	fmt.Println("%s:%s",k, v.(string))
  }
}

// map[AWS_ID:x12345123r2r4adefds AWS_KEY:test123]

// x12345123r2r4adefds
// test123

IO Reader

定義如下

type Reader interface {
    Read(p []byte) (n int, err error)
}

當讀取完後會出現 io.EOF

// ErrShortWrite means that a write accepted fewer bytes than requested
// but failed to return an explicit error.
var ErrShortWrite = errors.New("short write")

// ErrShortBuffer means that a read required a longer buffer than was provided.
var ErrShortBuffer = errors.New("short buffer")

// EOF is the error returned by Read when no more input is available.
// Functions should return EOF only to signal a graceful end of input.
// If the EOF occurs unexpectedly in a structured data stream,
// the appropriate error is either ErrUnexpectedEOF or some other error
// giving more detail.
var EOF = errors.New("EOF")

// ErrUnexpectedEOF means that EOF was encountered in the
// middle of reading a fixed-size block or data structure.
var ErrUnexpectedEOF = errors.New("unexpected EOF")

// ErrNoProgress is returned by some clients of an io.Reader when
// many calls to Read have failed to return any data or error,
// usually the sign of a broken io.Reader implementation.
var ErrNoProgress = errors.New("multiple Read calls return no data or error")

許多模組包含 strings 都有接入此 Read 接口

IO Write

通常會用 for loop 來讀取與寫入，或是可用 io.copy來替代。相較於先使用 readAll 然後 fPrintf 的方式，會導致記憶體洩漏，可用 io.copy 解決。

不錯的文章可參考：

對檔案的文字行進行操作

如果要進行文字細部操作可使用 bufio 模組。

https://openhome.cc/Gossip/Go/bufio.html

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