What might be wrong with the following small program?
func main() {
scanner := bufio.NewScanner(strings.NewReader(`one
two
three
four
`))
var (
text string
n int
)
for scanner.Scan() {
n++
text += fmt.Sprintf("%d. %s\n", n, scanner.Text())
}
fmt.Print(text)
// Output:
// 1. One
// 2. Two
// 3. Three
// 4. Four
}
The program numbers the lines in a buffer and uses the text/scanner
to read the input line-by-line. What might be wrong with it?
Answer:
First, it is not necessary to collect the input in the string before putting it out to standard output. This example is slightly contrived.
Second, the string text is not modified with the +=
operator, it is created anew for every line. This is a significant difference between strings and []byte
slices — strings in Go are non-modifiable. If you need to modify a string, use a []byte
slice.
Here’s a provided small program, written in a better way:
func main() {
scanner := bufio.NewScanner(strings.NewReader(`one
two
three
four
`))
var (
text []byte
n int
)
for scanner.Scan() {
n++
text = append(text, fmt.Sprintf("%d. %s\n", n, scanner.Text())...)
}
os.Stdout.Write(text)
// 1. One
// 2. Two
// 3. Three
// 4. Four
}
That is the point of the existence of both bytes
and strings
packages.