`Bufio.ScanBytes`

Suppose in Go we want to read each individual byte in a file. We can test, store or append (to a byte slice) each byte.

`NewScanner`

With bufio.NewScanner, we can call Split with an argument of bufio.ScanBytes. Then we call Scan and Bytes() to read each byte.

An example

To begin, we include the "bufio" and "os" packages to make sure our program will compile. We then use os.Open on the file path.

Start We create a new scanner with the bufio.NewScanner method—we pass in the file descriptor.

Important Split() sets the "splitting" method that controls how Scan() behaves. We use the built-in method ScanBytes on bufio.

Here We use a for-loop that calls Scan(). We call Bytes() on each iteration, which returns a 1-byte slice with the byte that was read.

package main

import (
    "bufio"
    "fmt"
    "os"
)

func BytesInFile(fileName string) {
    f, _ := os.Open(fileName)
    scanner := bufio.NewScanner(f)

    // Call Split to specify that we want to Scan each individual byte.
    scanner.Split(bufio.ScanBytes)

    // Use For-loop.
    for scanner.Scan() {
        // Get Bytes and display the byte.
        b := scanner.Bytes()
        fmt.Printf("%v = %v = %v\n", b, b[0], string(b))
    }
}

func main() {
    BytesInFile(`C:\programs\file.txt`)
}[84] = 84 = T
[104] = 104 = h
[97] = 97 = a
[110] = 110 = n
[107] = 107 = k
[32] = 32 =
[121] = 121 = y
[111] = 111 = o
[117] = 117 = u
[10] = 10 =

[70] = 70 = F
[114] = 114 = r
[105] = 105 = i
[101] = 101 = e
[110] = 110 = n
[100] = 100 = d

Notes, results

When we execute this program, it reads in the specified file. The file used in the example contains the strings "Thank you Friend."

And We see the ASCII representation of the file contents. The space and newline are also included.

A review

To create a byte slice containing the file data, we could append to an empty byte slice. This approach can be helpful if we need to test each individual byte as we read the file.