I haven't been able to find this anywhere (or I just don't understand it). I'm reading in a list of numbers from a file separated by spaces. I.e. the file looks like "1 4 0 0 2 5 ...etc", and I want it in the form of an array (or, preferably, a 2 dimensional array where each new line is separated as well). How might I go about doing this?
This is the code I have so far - a lot of it is taken from tutorials I found, so I don't fully understand all of it. It reads in a file just fine, and returns a string. Side question: when I print the string, I get this at the end of the output: %!(EXTRA ) Does anyone know how to fix that? I'm assuming it's putting the last nil character in the return string, but I don't know how to fix that.
package main
import (
"fmt"
"os"
)
func read_file(filename string) (string, os.Error) {
f, err := os.Open(filename)
if err != nil {
return "", err
}
defer f.Close() // f.Close will run when we're finished.
var result []byte
buf := make([]byte, 100)
for {
n, err := f.Read(buf[0:])
result = append(result, buf[0:n]...) // append is discussed later.
if err != nil {
if err == os.EOF {
break
}
return "", err // f will be closed if we return here.
}
}
return string(result), nil // f will be closed if we return here.
}
func print_board() {
}
func main() {
fmt.Printf(read_file("sudoku1.txt")) // this outputs the file exactly,
// but with %!(EXTRA <nil>) at the end.
// I do not know why exactly
}
Thank you very much for any help you can offer.
-W
You can use the strings package to convert the string to a 2 dimensional array of ints. Explaining some of the language constructs used here is a bit outside the scope of this question, but feel free to ask for clarification on anything.
// read_file also returns an error!
s, err := read_file("sudoku1.txt")
if err != nil {
panic(err.String())
}
// split into rows at newlines
rows := strings.Split(s, "
")
board := make([][]int, len(rows))
for i, row := range rows {
// extract all whitespace separated fields
elems := strings.Fields(row)
board[i] = make([]int, len(elems))
for j, elem := range elems {
var err os.Error
// convert each element to an integer
board[i][j], err = strconv.Atoi(elem)
if err != nil {
panic(err.String())
}
}
}
fmt.Println(board)
The reason for the %(!EXTRA <nil>) is that read_file returns two values, the second being an error (which is nil in this case). Printf tries to match that second value to a slot in the string. Since the string doesn't contain any formatting slots (%v, %d, %s...), Printf determines that it is an extra parameter, and says that in the output.
Note that the package ioutil already provides a ReadFile function, which will give you a []byte instead of a string, but is otherwise identical in function to your read_file.