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54-读文件.go
58 lines (47 loc) · 1.8 KB
/
54-读文件.go
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package main
import (
"bufio"
"fmt"
"io"
"io/ioutil"
"os"
)
//Reading files requires checking most calls for errors.This helper will streamline our error checks below.
func main() {
//Perhaps the most basic file reading task is slurping a file’s entire contents into memory.
dat, err := ioutil.ReadFile("haha.txt")
check(err)
fmt.Print(string(dat))
//You’ll often want more control over how and what parts of a file are read. For these tasks, start by Opening a file to obtain an os.File value.
f, err := os.Open("haha.txt")
check(err)
//Read some bytes from the beginning of the file. Allow up to 5 to be read but also note how many actually were read.
b1 := make([]byte, 5)
n1, err := f.Read(b1)
check(err)
fmt.Printf("%d bytes: %s\n", n1, string(b1))
//You can also Seek to a known location in the file and Read from there.
o2, err := f.Seek(6, 0)
check(err)
b2 := make([]byte, 2)
n2, err := f.Read(b2)
check(err)
fmt.Printf("%d bytes @ %d: %s\n", n2, o2, string(b2))
//The io package provides some functions that may be helpful for file reading. For example, reads like the ones above can be more robustly implemented with ReadAtLeast.
o3, err := f.Seek(6, 0)
check(err)
b3 := make([]byte, 2)
n3, err := io.ReadAtLeast(f, b3, 2)
check(err)
fmt.Printf("%d bytes @ %d: %s\n", n3, o3, string(b3))
//There is no built-in rewind, but Seek(0, 0) accomplishes this.
_, err = f.Seek(0, 0)
check(err)
//The bufio package implements a buffered reader that may be useful both for its efficiency with many small reads and because of the additional reading methods it provides.
r4 := bufio.NewReader(f)
b4, err := r4.Peek(5)
check(err)
fmt.Printf("5 bytes: %s\n", string(b4))
//Close the file when you’re done (usually this would be scheduled immediately after Opening with defer).
f.Close()
}