首次写入后写入终止符（即ox1e）失败

Question

I have some data (MARC record actually) that I'm trying to create using go (version 1.9.2) and I can't figure out how to get the delimiting characters written to the output file.

The snippet below is an example of the closest that I've been able to come up with. The first item gets written with the appropriate terminator but nothing else after that.

What is the best/correct way to write these kinds of terminator characters in go?

const fieldTerminator = 0x1e

func main() {
    data := []string{"item one", "item two", "item tre"}

    writer, err := os.Create("x.out")
    if err != nil {
        log.Fatalf("Could not open file: %q
", err)
    }
    defer writer.Close() // per biosckon

    ft := make([]byte, 2)
    binary.LittleEndian.PutUint16(ft, uint16(fieldTerminator))

    for _, d := range data {
        // this just proves to me that the loop is working
        //os.Stderr.WriteString(fmt.Sprintf("d is %q
", d))
        fmt.Fprintf(os.Stderr, "d is %q
", d) // per Andy Schweig

        _, err := writer.Write([]byte(d))
        if err != nil {
            log.Fatalf("%q
", err)
        }

        // This prints the correct character at the end of the first item
        // and nothing after that (items 2 and 3 not printed, no errors):
        _, err = writer.Write(ft)
        if err != nil {
            log.Fatalf("%q
", err)
        }
    }
}

Edit: updated code snippet to address suggestions by Andy Schweig and biosckon.

Answer 1

The problem is with how binary.LittleEndian.PutUint16 was being used.

What is required is a single byte for the field terminator. The result of PutUint16 is two bytes, the terminator byte and a null byte (PutUint16 doesn't work if ft is defined as one byte and there is no PutUint8). So the fix is to truncate ft after the fact to remove the null byte.

The following works as required:

const fieldTerminator = 0x1e

func main() {
    data := []string{"item one", "item two", "item tre"}

    writer, err := os.Create("x.out")
    if err != nil {
        log.Fatalf("Could not open file: %q
", err)
    }
    defer writer.Close()

    ft := make([]byte, 2)
    binary.LittleEndian.PutUint16(ft, uint16(fieldTerminator))
    ft = ft[:1] // Truncate ft to a single byte

    for _, d := range data {
        _, err := writer.Write([]byte(d))
        if err != nil {
            log.Fatalf("%q
", err)
        }

        _, err = writer.Write(ft)
        if err != nil {
            log.Fatalf("%q
", err)
        }
    }
}