I have a empty file called a.txt
, I want to output a value(int) to it in a loop, and overwrite last content in file a.txt
. For example,
// open a file
f, err := os.Open("test.txt")
if err != nil {
log.Fatal(err)
}
defer f.Close()
// another file
af, err := os.OpenFile("a.txt", os.O_WRONLY|os.O_CREATE|os.O_TRUNC, 0644)
if err != nil {
log.Fatal(err)
}
defer af.Close()
b := []byte{}
scanner := bufio.NewScanner(f)
for scanner.Scan() {
b = append(b, scanner.Bytes()...)
// how to output len(b) into a.txt?
}
Just use the truncate method and write again to file starting at the begining.
err = f.Truncate(0)
_, err = f.Seek(0, 0)
_, err = fmt.Fprintf(f, "%d", len(b))