Count lines via bufio - go

Question

I'm utilizing bufio to do a for loop for each line in a text file. I have no idea how to count the amount of lines though.
scanner := bufio.NewScanner(bufio.NewReader(file))
The above is what I use to scan my file.

Answer 1

You could do something like this:
counter := 0
for scanner.Scan() {
line := scanner.Text()
counter++
// do something with your line
}
fmt.Printf("Lines read: %d", counter)

Answer 2

Keep it simple and fast. No need for buffering, scanner already does that. Don't do unnecessary string conversions. For example,
package main
import (
"bufio"
"fmt"
"os"
)
func lineCount(filename string) (int64, error) {
lc := int64(0)
f, err := os.Open(filename)
if err != nil {
return 0, err
}
defer f.Close()
s := bufio.NewScanner(f)
for s.Scan() {
lc++
}
return lc, s.Err()
}
func main() {
filename := `testfile`
lc, err := lineCount(filename)
if err != nil {
fmt.Println(err)
return
}
fmt.Println(filename+" line count:", lc)
}

Answer 3

As I commented, the accepted answer fails at long lines. The default limit is bufio.MaxScanTokenSize which is 64KiB. So if your line is longer than 65536 chars, it will silently fail. You've got two options.
Call scanner.Buffer() and supply the sufficient max parameter. buffer may be small by default because Scanner is smart enough to allocate new ones. Can be a problem if you don't know the total size beforehand, like with vanilla Reader interface, and you've got huge lines - the memory consumption will grow correspondingly as Scanner records all the line.
Recreate scanner in the outer loop, this will ensure that you advance further:
var scanner *bufio.Scanner
counter := 0
for scanner == nil || scanner.Err() == bufio.ErrTooLong {
scanner = bufio.NewScanner(reader)
for scanner.Scan() {
counter++
}
}
The problem with (2) is that you keep allocating and deallocating buffers instead of reusing them. So let's fuse (1) and (2):
var scanner *bufio.Scanner
buffer := make([]byte, bufio.MaxScanTokenSize)
counter := 0
for scanner == nil || scanner.Err() == bufio.ErrTooLong {
scanner = bufio.NewScanner(reader)
scanner.Buffer(buffer, 0)
for scanner.Scan() {
counter++
}
}

Answer 4

Here is my approach to do the task:
inputFile, err := os.Open("input.txt")
if err != nil {
panic("Error happend during opening the file. Please check if file exists!")
os.Exit(1)
}
defer inputFile.Close()
inputReader := bufio.NewReader(inputFile)
scanner := bufio.NewScanner(inputReader)
// Count the words.
count := 0
for scanner.Scan() {
line := scanner.Text()
fmt.Printf("%v\n", line)
count++
}
if err := scanner.Err(); err != nil {
fmt.Fprintln(os.Stderr, "reading input:", err)
}
fmt.Printf("%d\n", count)