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The Way to Go

Reading and Writing Files with Slices

This lesson explains in detail how to use a slice for reading and writing to files.

We'll cover the following...

Slices provide the standard-Go way to handle I/O buffers; they are used in the following second version of the function cat, which reads a file in an infinite for-loop (until end-of-file EOF) in a sliced buffer, and writes it to standard output.

Go (1.6.2)
func cat(f *os.File) {

  const NBUF = 512

  var buf [NBUF]byte

  for {

    switch nr, err := f.Read(buf[:]); true {

    case nr < 0:

      fmt.Fprintf(os.Stderr, "cat: error reading: %s\n", err.Error())

      os.Exit(1)

    case nr == 0: // EOF

      return

    case nr > 0:

      if nw, ew := os.Stdout.Write(buf[0:nr]); nw != nr {

        fmt.Fprintf(os.Stderr, "cat: error writing: %s\n")

      }

    }

  }

}

Look at the following example:

Welcome to Educative

Click the RUN button, and wait for the terminal to start. Type go run main.go test.txt and press ENTER.

This program is mostly the ...