使用io/ioutil进行读写文件
ioutil包
其中提到了两个方法：
func ReadFilefunc ReadFile(filename string) ([]byte, error)
ReadFile reads the file named by filename and returns the contents. A successful call returns err == nil, not err == EOF. Because ReadFile reads the whole file, it does not treat an EOF from Read as an error to be reported.
func WriteFile
func WriteFile(filename string, data []byte, perm os.FileMode) error
WriteFile writes data to a file named by filename. If the file does not exist, WriteFile creates it with permissions perm; otherwise WriteFile truncates it before writing
读文件：
package mainimport ( "fmt" "io/ioutil")func main() { b, err := ioutil.ReadFile("test.log") if err != nil { fmt.Print(err) } fmt.Println(b) str := string(b) fmt.Println(str)} 写文件：
package mainimport ( "io/ioutil")func check(e error) { if e != nil { panic(e) }}func main() { d1 := []byte("hello\ngo\n") err := ioutil.WriteFile("test.txt", d1, 0644) check(err)}
使用os进行读写文件
os包
首先要注意的就是两个打开文件的方法：
func Open
func Open(name string) (*File, error)
Open opens the named file for reading. If successful, methods on the returned file can be used for reading; the associated file descriptor has mode O_RDONLY. If there is an error, it will be of type *PathError.
读文件：
fi, err := os.Open(path) if err != nil { panic(err) } defer fi.Close() func OpenFile
需要提供文件路径、打开模式、文件权限func OpenFile(name string, flag int, perm FileMode) (*File, error)
OpenFile is the generalized open call; most users will use Open or Create instead. It opens the named file with specified flag (O_RDONLY etc.) and perm, (0666 etc.) if applicable. If successful, methods on the returned File can be used for I/O. If there is an error, it will be of type *PathError.
读文件：
package mainimport ( "log" "os")func main() { f, err := os.OpenFile("notes.txt", os.O_RDWR|os.O_CREATE, 0755) if err != nil { log.Fatal(err) } if err := f.Close(); err != nil { log.Fatal(err) }} 读方法
package mainimport ( "bufio" "fmt" "io" "os")func check(e error) { if e != nil { panic(e) }}func main() { f, err := os.Open("foo.dat") check(err) b1 := make([]byte, 5) n1, err := f.Read(b1) check(err) fmt.Printf("%d bytes: %s\n", n1, string(b1)) 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)) 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)) _, err = f.Seek(0, 0) check(err) r4 := bufio.NewReader(f) b4, err := r4.Peek(5) check(err) fmt.Printf("5 bytes: %s\n", string(b4)) f.Close()} 写方法
package mainimport ( "bufio" "fmt" "os")func check(e error) { if e != nil { panic(e) }}func main() { f, err := os.Create("/tmp/dat2") check(err) defer f.Close() d2 := []byte{115, 111, 109, 101, 10} n2, err := f.Write(d2) check(err) fmt.Printf("wrote %d bytes\n", n2) n3, err := f.WriteString("writes\n") fmt.Printf("wrote %d bytes\n", n3) f.Sync() w := bufio.NewWriter(f) n4, err := w.WriteString("buffered\n") fmt.Printf("wrote %d bytes\n", n4) w.Flush()}
几种读取文件方法速度比较
package main
import (
"bufio"
"fmt"
"io"
"io/ioutil"
"os"
"time"
)
func read0(path string) string { f, err := ioutil.ReadFile(path)
if err != nil { fmt.Printf("%s\n", err) panic(err)
}
return string(f)
}
func read1(path string) string { fi, err := os.Open(path)
if err != nil { panic(err)
}
defer fi.Close()
chunks := make([]byte, 1024, 1024)
buf := make([]byte, 1024)
for { n, err := fi.Read(buf)
if err != nil && err != io.EOF { panic(err)
}
if 0 == n { break
}
chunks = append(chunks, buf[:n]...)
}
return string(chunks)
}
func read2(path string) string { fi, err := os.Open(path)
if err != nil { panic(err)
}
defer fi.Close()
r := bufio.NewReader(fi)
chunks := make([]byte, 1024, 1024)
buf := make([]byte, 1024)
for { n, err := r.Read(buf)
if err != nil && err != io.EOF { panic(err)
}
if 0 == n { break
}
chunks = append(chunks, buf[:n]...)
}
return string(chunks)
}
func read3(path string) string { fi, err := os.Open(path)
if err != nil { panic(err)
}
defer fi.Close()
fd, err := ioutil.ReadAll(fi)
return string(fd)
}
func main() { file := "foo.dat"
start := time.Now()
read0(file)
t0 := time.Now()
fmt.Printf("Cost time %v\n", t0.Sub(start)) read1(file)
t1 := time.Now()
fmt.Printf("Cost time %v\n", t1.Sub(t0)) read2(file)
t2 := time.Now()
fmt.Printf("Cost time %v\n", t2.Sub(t1)) read3(file)
t3 := time.Now()
fmt.Printf("Cost time %v\n", t3.Sub(t2)) }