Reading input from stdin in golang - go

Question

I have this go code:
func readTwoLines() {
reader := bufio.NewReader(os.Stdin)
line, _ := reader.ReadString('\n')
fmt.Println(line)
line, _ = reader.ReadString('\n')
fmt.Println(line)
}
For the input:
hello
bye
the output is:
hello
bye
Everything ok. But now, if I create one reader per line:
func readTwoLines() {
line, _ := bufio.NewReader(os.Stdin).ReadString('\n')
fmt.Println(line)
line, err := bufio.NewReader(os.Stdin).ReadString('\n')
if err != nil {
fmt.Println(err)
}
fmt.Println(line)
}
there is an EOF error, in the second line reading.
Why is it happening?

Answer 1

For simple uses, a Scanner may be more convenient.
You should not use two readers, first read, buffers 4096 bytes of input:
// NewReader returns a new Reader whose buffer has the default size.
func NewReader(rd io.Reader) *Reader {
return NewReaderSize(rd, defaultBufSize)
}
and defaultBufSize = 4096
and even your input contains 4000 bytes, still second read got nothing to read.
but if you enter input more than 4096 bytes it will work.
If ReadString encounters an error before finding a delimiter, it
returns the data read before the error and the error itself (often
io.EOF).
it is by design, see doc:
// ReadString reads until the first occurrence of delim in the input,
// returning a string containing the data up to and including the delimiter.
// If ReadString encounters an error before finding a delimiter,
// it returns the data read before the error and the error itself (often io.EOF).
// ReadString returns err != nil if and only if the returned data does not end in
// delim.
// For simple uses, a Scanner may be more convenient.
func (b *Reader) ReadString(delim byte) (string, error) {
bytes, err := b.ReadBytes(delim)
return string(bytes), err
}
try this:
package main
import (
"bufio"
"fmt"
"os"
)
func main() {
scanner := bufio.NewScanner(os.Stdin)
for scanner.Scan() {
fmt.Println(scanner.Text()) // Println will add back the final '\n'
}
if err := scanner.Err(); err != nil {
fmt.Fprintln(os.Stderr, "reading standard input:", err)
}
}
run:
go run m.go < in.txt
output:
hello
bye
in.txt file:
hello
bye
I hope this helps.