No, I would not consider that safe. While it works now, the documentation states that the function reserves the right to read past the value by one character unless you have an UnreadRune()
method.
By wrapping your reader in a bufio.Reader
, you can ensure the reader has an UnreadRune()
method. You will then need to read the final whitespace yourself.
buf := bufio.NewReader(input)
fmt.Fscanf(buf,"%2s %d %d %d",&magic,&width,&height,&maxVal)
buf.ReadRune() // remove next rune (the whitespace) from the buffer.
Edit:
As we discussed in the chat, you can assume the dummy char method works and then write a test so you know when it stops working. The test can be something like:
func TestFmtBehavior(t *testing.T) {
// use multireader to prevent r from implementing io.RuneScanner
r := io.MultiReader(bytes.NewReader([]byte("data ")))
n, err := fmt.Fscanf(r, "%s%c", new(string), new(byte))
if n != 2 || err != nil {
t.Error("failed scan", n, err)
}
// the dummy char read 1 extra char past "data".
// one byte should still remain
if n, err := r.Read(make([]byte, 5)); n != 1 {
t.Error("assertion failed", n, err)
}
}