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# バイト列を整数に変換する簡単なお仕事メモ（Go言語）

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バイト列を整数に変換する簡単なお仕事。

```package main

import (
"encoding/binary"
"fmt"
)

func main() {
octets := []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07}

fmt.Printf("%#016x\n", binary.BigEndian.Uint64(octets))    //0x0001020304050607
fmt.Printf("%#016x\n", binary.LittleEndian.Uint64(octets)) //0x0706050403020100
}
```

```package main

import (
"encoding/binary"
"fmt"
)

func main() {
value := uint64(0x0706050403020100)
buf := make([]byte, binary.MaxVarintLen64) //MaxVarintLen64 = 10

binary.BigEndian.PutUint64(buf, value)
fmt.Println(buf[:8]) //[7 6 5 4 3 2 1 0]
binary.LittleEndian.PutUint64(buf, value)
fmt.Println(buf[:8]) //[0 1 2 3 4 5 6 7]

}
```

なんちうか今まですンごい回りくどい記述してたよ。わざわざ `bytes.NewReader(octets)` でラップするとか。

```package main

import (
"bytes"
"encoding/binary"
"fmt"
)

func main() {
octets := []byte{0x00, 0x01, 0x02, 0x03, 0x04, 0x05, 0x06, 0x07}
var value uint64

if err := binary.Read(bytes.NewReader(octets), binary.LittleEndian, &value); err != nil {
return
}
fmt.Printf("%#016x\n", value) //0x0706050403020100
}
```

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