Golang: How do I determine the number of lines in a file efficiently?

Question

In Golang, I am looking for an efficient way to determine the number of lines a file has.

Of course, I can always loop through the entire file, but does not seem ver

Answer 1

There is no approach that is significantly faster than yours as there is no meta-data on how many lines a file has. You could reach a little speed up by manually looking for newline-characters:

func lineCount(r io.Reader) (int n, error err) {
    buf := make([]byte, 8192)

    for {
        c, err := r.Read(buf)
        if err != nil {
            if err == io.EOF && c == 0 {
                break
            } else {
                return
            }
        }

        for _, b := range buf[:c] {
            if b == '\n' {
                n++
            }
        }
    }

    if err == io.EOF {
        err = nil
    }
}