# 18.7 文件 （1）如何打開一個文件并讀取： ``` file, err := os.Open("input.dat") if err != nil { fmt.Printf("An error occurred on opening the inputfile\n" + "Does the file exist?\n" + "Have you got acces to it?\n") return } defer file.Close() iReader := bufio.NewReader(file) for { str, err := iReader.ReadString('\n') if err != nil { return // error or EOF } fmt.Printf("The input was: %s", str) } ``` （2）如何通過切片讀寫文件： ``` func cat(f *file.File) { const NBUF = 512 var buf [NBUF]byte for { switch nr, er := f.Read(buf[:]); true { case nr < 0: fmt.Fprintf(os.Stderr, "cat: error reading from %s: %s\n", f.String(), er.String()) os.Exit(1) case nr == 0: // EOF return case nr > 0: if nw, ew := file.Stdout.Write(buf[0:nr]); nw != nr { fmt.Fprintf(os.Stderr, "cat: error writing from %s: %s\n", f.String(), ew.String()) } } } } ```