如何将字符串写入二进制文件？

such as, I write 'A' but in file it is '1000001' ,

how can I do ?

I have tried

    buf := new(bytes.Buffer)

    data := []int8{65, 80}

    for _, i := range data {
        binary.Write(buf, binary.LittleEndian, i)

        fp.Write(buf.Bytes())
    }

but I got string 'AP' in file not a binary code

I didn't really understand the question, but perhaps you want something like:

package main

import (
    "fmt"
    "log"
    "os"
)

func main() {
    f, err := os.OpenFile("out.txt", os.O_TRUNC|os.O_CREATE|os.O_WRONLY, 0600)
    if err != nil {
        log.Fatal(err)
    }
    for _, v := range "AP" {
        fmt.Fprintf(f, "%b
", v)
    }
    f.Close()
}

which gives:

$ cat out.txt
1000001
1010000