go【第八篇】操作文件

借助模块：io/bufio os

源码剖析

// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package os provides a platform-independent interface to operating system
// functionality. The design is Unix-like, although the error handling is
// Go-like; failing calls return values of type error rather than error numbers.
// Often, more information is available within the error. For example,
// if a call that takes a file name fails, such as Open or Stat, the error
// will include the failing file name when printed and will be of type
// *PathError, which may be unpacked for more information.
//
// The os interface is intended to be uniform across all operating systems.
// Features not generally available appear in the system-specific package syscall.
//
// Here is a simple example, opening a file and reading some of it.
//
//    file, err := os.Open("file.go") // For read access.
//    if err != nil {
//        log.Fatal(err)
//    }
//
// If the open fails, the error string will be self-explanatory, like
//
//    open file.go: no such file or directory
//
// The file's data can then be read into a slice of bytes. Read and
// Write take their byte counts from the length of the argument slice.
//
//    data := make([]byte, 100)
//    count, err := file.Read(data)
//    if err != nil {
//        log.Fatal(err)
//    }
//    fmt.Printf("read %d bytes: %q\n", count, data[:count])
//
package os

import (
    "errors"
    "internal/poll"
    "internal/testlog"
    "io"
    "runtime"
    "syscall"
    "time"
)

// Name returns the name of the file as presented to Open.
func (f *File) Name() string { return f.name }

// Stdin, Stdout, and Stderr are open Files pointing to the standard input,
// standard output, and standard error file descriptors.
//
// Note that the Go runtime writes to standard error for panics and crashes;
// closing Stderr may cause those messages to go elsewhere, perhaps
// to a file opened later.
var (
    Stdin  = NewFile(uintptr(syscall.Stdin), "/dev/stdin")
    Stdout = NewFile(uintptr(syscall.Stdout), "/dev/stdout")
    Stderr = NewFile(uintptr(syscall.Stderr), "/dev/stderr")
)

// Flags to OpenFile wrapping those of the underlying system. Not all
// flags may be implemented on a given system.
const (
    // Exactly one of O_RDONLY, O_WRONLY, or O_RDWR must be specified.
    O_RDONLY int = syscall.O_RDONLY // open the file read-only.
    O_WRONLY int = syscall.O_WRONLY // open the file write-only.
    O_RDWR   int = syscall.O_RDWR   // open the file read-write.
    // The remaining values may be or'ed in to control behavior.
    O_APPEND int = syscall.O_APPEND // append data to the file when writing.
    O_CREATE int = syscall.O_CREAT  // create a new file if none exists.
    O_EXCL   int = syscall.O_EXCL   // used with O_CREATE, file must not exist.
    O_SYNC   int = syscall.O_SYNC   // open for synchronous I/O.
    O_TRUNC  int = syscall.O_TRUNC  // truncate regular writable file when opened.
)

// Seek whence values.
//
// Deprecated: Use io.SeekStart, io.SeekCurrent, and io.SeekEnd.
const (
    SEEK_SET int = 0 // seek relative to the origin of the file
    SEEK_CUR int = 1 // seek relative to the current offset
    SEEK_END int = 2 // seek relative to the end
)

// LinkError records an error during a link or symlink or rename
// system call and the paths that caused it.
type LinkError struct {
    Op  string
    Old string
    New string
    Err error
}

func (e *LinkError) Error() string {
    return e.Op + " " + e.Old + " " + e.New + ": " + e.Err.Error()
}

// Read reads up to len(b) bytes from the File.
// It returns the number of bytes read and any error encountered.
// At end of file, Read returns 0, io.EOF.
func (f *File) Read(b []byte) (n int, err error) {
    if err := f.checkValid("read"); err != nil {
        return 0, err
    }
    n, e := f.read(b)
    return n, f.wrapErr("read", e)
}

// ReadAt reads len(b) bytes from the File starting at byte offset off.
// It returns the number of bytes read and the error, if any.
// ReadAt always returns a non-nil error when n < len(b).
// At end of file, that error is io.EOF.
func (f *File) ReadAt(b []byte, off int64) (n int, err error) {
    if err := f.checkValid("read"); err != nil {
        return 0, err
    }

    if off < 0 {
        return 0, &PathError{"readat", f.name, errors.New("negative offset")}
    }

    for len(b) > 0 {
        m, e := f.pread(b, off)
        if e != nil {
            err = f.wrapErr("read", e)
            break
        }
        n += m
        b = b[m:]
        off += int64(m)
    }
    return
}

// Write writes len(b) bytes to the File.
// It returns the number of bytes written and an error, if any.
// Write returns a non-nil error when n != len(b).
func (f *File) Write(b []byte) (n int, err error) {
    if err := f.checkValid("write"); err != nil {
        return 0, err
    }
    n, e := f.write(b)
    if n < 0 {
        n = 0
    }
    if n != len(b) {
        err = io.ErrShortWrite
    }

    epipecheck(f, e)

    if e != nil {
        err = f.wrapErr("write", e)
    }

    return n, err
}

// WriteAt writes len(b) bytes to the File starting at byte offset off.
// It returns the number of bytes written and an error, if any.
// WriteAt returns a non-nil error when n != len(b).
func (f *File) WriteAt(b []byte, off int64) (n int, err error) {
    if err := f.checkValid("write"); err != nil {
        return 0, err
    }

    if off < 0 {
        return 0, &PathError{"writeat", f.name, errors.New("negative offset")}
    }

    for len(b) > 0 {
        m, e := f.pwrite(b, off)
        if e != nil {
            err = f.wrapErr("write", e)
            break
        }
        n += m
        b = b[m:]
        off += int64(m)
    }
    return
}

// Seek sets the offset for the next Read or Write on file to offset, interpreted
// according to whence: 0 means relative to the origin of the file, 1 means
// relative to the current offset, and 2 means relative to the end.
// It returns the new offset and an error, if any.
// The behavior of Seek on a file opened with O_APPEND is not specified.
func (f *File) Seek(offset int64, whence int) (ret int64, err error) {
    if err := f.checkValid("seek"); err != nil {
        return 0, err
    }
    r, e := f.seek(offset, whence)
    if e == nil && f.dirinfo != nil && r != 0 {
        e = syscall.EISDIR
    }
    if e != nil {
        return 0, f.wrapErr("seek", e)
    }
    return r, nil
}

// WriteString is like Write, but writes the contents of string s rather than
// a slice of bytes.
func (f *File) WriteString(s string) (n int, err error) {
    return f.Write([]byte(s))
}

// Mkdir creates a new directory with the specified name and permission
// bits (before umask).
// If there is an error, it will be of type *PathError.
func Mkdir(name string, perm FileMode) error {
    e := syscall.Mkdir(fixLongPath(name), syscallMode(perm))

    if e != nil {
        return &PathError{"mkdir", name, e}
    }

    // mkdir(2) itself won't handle the sticky bit on *BSD and Solaris
    if !supportsCreateWithStickyBit && perm&ModeSticky != 0 {
        e = setStickyBit(name)

        if e != nil {
            Remove(name)
            return e
        }
    }

    return nil
}

// setStickyBit adds ModeSticky to the permision bits of path, non atomic.
func setStickyBit(name string) error {
    fi, err := Stat(name)
    if err != nil {
        return err
    }
    return Chmod(name, fi.Mode()|ModeSticky)
}

// Chdir changes the current working directory to the named directory.
// If there is an error, it will be of type *PathError.
func Chdir(dir string) error {
    if e := syscall.Chdir(dir); e != nil {
        testlog.Open(dir) // observe likely non-existent directory
        return &PathError{"chdir", dir, e}
    }
    if log := testlog.Logger(); log != nil {
        wd, err := Getwd()
        if err == nil {
            log.Chdir(wd)
        }
    }
    return nil
}

// 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.
func Open(name string) (*File, error) {
    return OpenFile(name, O_RDONLY, 0)
}

// Create creates the named file with mode 0666 (before umask), truncating
// it if it already exists. If successful, methods on the returned
// File can be used for I/O; the associated file descriptor has mode
// O_RDWR.
// If there is an error, it will be of type *PathError.
func Create(name string) (*File, error) {
    return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
}

// 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 (before umask), 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.
func OpenFile(name string, flag int, perm FileMode) (*File, error) {
    testlog.Open(name)
    return openFileNolog(name, flag, perm)
}

// lstat is overridden in tests.
var lstat = Lstat

// Rename renames (moves) oldpath to newpath.
// If newpath already exists and is not a directory, Rename replaces it.
// OS-specific restrictions may apply when oldpath and newpath are in different directories.
// If there is an error, it will be of type *LinkError.
func Rename(oldpath, newpath string) error {
    return rename(oldpath, newpath)
}

// Many functions in package syscall return a count of -1 instead of 0.
// Using fixCount(call()) instead of call() corrects the count.
func fixCount(n int, err error) (int, error) {
    if n < 0 {
        n = 0
    }
    return n, err
}

// wrapErr wraps an error that occurred during an operation on an open file.
// It passes io.EOF through unchanged, otherwise converts
// poll.ErrFileClosing to ErrClosed and wraps the error in a PathError.
func (f *File) wrapErr(op string, err error) error {
    if err == nil || err == io.EOF {
        return err
    }
    if err == poll.ErrFileClosing {
        err = ErrClosed
    }
    return &PathError{op, f.name, err}
}

// TempDir returns the default directory to use for temporary files.
//
// On Unix systems, it returns $TMPDIR if non-empty, else /tmp.
// On Windows, it uses GetTempPath, returning the first non-empty
// value from %TMP%, %TEMP%, %USERPROFILE%, or the Windows directory.
// On Plan 9, it returns /tmp.
//
// The directory is neither guaranteed to exist nor have accessible
// permissions.
func TempDir() string {
    return tempDir()
}

// UserCacheDir returns the default root directory to use for user-specific
// cached data. Users should create their own application-specific subdirectory
// within this one and use that.
//
// On Unix systems, it returns $XDG_CACHE_HOME as specified by
// https://standards.freedesktop.org/basedir-spec/basedir-spec-latest.html if
// non-empty, else $HOME/.cache.
// On Darwin, it returns $HOME/Library/Caches.
// On Windows, it returns %LocalAppData%.
// On Plan 9, it returns $home/lib/cache.
//
// If the location cannot be determined (for example, $HOME is not defined),
// then it will return an error.
func UserCacheDir() (string, error) {
    var dir string

    switch runtime.GOOS {
    case "windows":
        dir = Getenv("LocalAppData")
        if dir == "" {
            return "", errors.New("%LocalAppData% is not defined")
        }

    case "darwin":
        dir = Getenv("HOME")
        if dir == "" {
            return "", errors.New("$HOME is not defined")
        }
        dir += "/Library/Caches"

    case "plan9":
        dir = Getenv("home")
        if dir == "" {
            return "", errors.New("$home is not defined")
        }
        dir += "/lib/cache"

    default: // Unix
        dir = Getenv("XDG_CACHE_HOME")
        if dir == "" {
            dir = Getenv("HOME")
            if dir == "" {
                return "", errors.New("neither $XDG_CACHE_HOME nor $HOME are defined")
            }
            dir += "/.cache"
        }
    }

    return dir, nil
}

// UserHomeDir returns the current user's home directory.
//
// On Unix, including macOS, it returns the $HOME environment variable.
// On Windows, it returns %USERPROFILE%.
// On Plan 9, it returns the $home environment variable.
func UserHomeDir() (string, error) {
    env, enverr := "HOME", "$HOME"
    switch runtime.GOOS {
    case "windows":
        env, enverr = "USERPROFILE", "%userprofile%"
    case "plan9":
        env, enverr = "home", "$home"
    case "nacl", "android":
        return "/", nil
    case "darwin":
        if runtime.GOARCH == "arm" || runtime.GOARCH == "arm64" {
            return "/", nil
        }
    }
    if v := Getenv(env); v != "" {
        return v, nil
    }
    return "", errors.New(enverr + " is not defined")
}

// Chmod changes the mode of the named file to mode.
// If the file is a symbolic link, it changes the mode of the link's target.
// If there is an error, it will be of type *PathError.
//
// A different subset of the mode bits are used, depending on the
// operating system.
//
// On Unix, the mode's permission bits, ModeSetuid, ModeSetgid, and
// ModeSticky are used.
//
// On Windows, the mode must be non-zero but otherwise only the 0200
// bit (owner writable) of mode is used; it controls whether the
// file's read-only attribute is set or cleared. attribute. The other
// bits are currently unused. Use mode 0400 for a read-only file and
// 0600 for a readable+writable file.
//
// On Plan 9, the mode's permission bits, ModeAppend, ModeExclusive,
// and ModeTemporary are used.
func Chmod(name string, mode FileMode) error { return chmod(name, mode) }

// Chmod changes the mode of the file to mode.
// If there is an error, it will be of type *PathError.
func (f *File) Chmod(mode FileMode) error { return f.chmod(mode) }

// SetDeadline sets the read and write deadlines for a File.
// It is equivalent to calling both SetReadDeadline and SetWriteDeadline.
//
// Only some kinds of files support setting a deadline. Calls to SetDeadline
// for files that do not support deadlines will return ErrNoDeadline.
// On most systems ordinary files do not support deadlines, but pipes do.
//
// A deadline is an absolute time after which I/O operations fail with an
// error instead of blocking. The deadline applies to all future and pending
// I/O, not just the immediately following call to Read or Write.
// After a deadline has been exceeded, the connection can be refreshed
// by setting a deadline in the future.
//
// An error returned after a timeout fails will implement the
// Timeout method, and calling the Timeout method will return true.
// The PathError and SyscallError types implement the Timeout method.
// In general, call IsTimeout to test whether an error indicates a timeout.
//
// An idle timeout can be implemented by repeatedly extending
// the deadline after successful Read or Write calls.
//
// A zero value for t means I/O operations will not time out.
func (f *File) SetDeadline(t time.Time) error {
    return f.setDeadline(t)
}

// SetReadDeadline sets the deadline for future Read calls and any
// currently-blocked Read call.
// A zero value for t means Read will not time out.
// Not all files support setting deadlines; see SetDeadline.
func (f *File) SetReadDeadline(t time.Time) error {
    return f.setReadDeadline(t)
}

// SetWriteDeadline sets the deadline for any future Write calls and any
// currently-blocked Write call.
// Even if Write times out, it may return n > 0, indicating that
// some of the data was successfully written.
// A zero value for t means Write will not time out.
// Not all files support setting deadlines; see SetDeadline.
func (f *File) SetWriteDeadline(t time.Time) error {
    return f.setWriteDeadline(t)
}

// SyscallConn returns a raw file.
// This implements the syscall.Conn interface.
func (f *File) SyscallConn() (syscall.RawConn, error) {
    if err := f.checkValid("SyscallConn"); err != nil {
        return nil, err
    }
    return newRawConn(f)
}

新建文件

func Create(name string) (*File, error) {
	return OpenFile(name, O_RDWR|O_CREATE|O_TRUNC, 0666)
}
根据提供的文件名创建新的文件，返回一个文件对象，默认权限是0666的文件，返回的文件对象是可读写的。

func NewFile(fd uintptr, name string) *File {
	kind := kindNewFile
	if nb, err := unix.IsNonblock(int(fd)); err == nil && nb {
		kind = kindNonBlock
	}
	return newFile(fd, name, kind)
}
根据文件描述符创建相应的文件，返回一个文件对象

package main

import (
    "os"
    "fmt"
)

func main()  {
    // 创建文件，需要指定文件的存储路径以及文件名称，注意“/”
    file,err:=os.Create("a.txt")
    //判断是否出现异常
    if err!=nil{
        fmt.Println(err)
        //file.Close()
    }
    defer file.Close()
    //对创建的文件进行相关的操作。

    //关闭
    //file.Close()

}

打开文件

func Open(name string) (*File, error) {
	return OpenFile(name, O_RDONLY, 0)
}
该方法打开一个名称为name的文件，但是是只读方式，内部实现其实调用了OpenFile。

func OpenFile(name string, flag int, perm FileMode) (*File, error) {
	testlog.Open(name)
	return openFileNolog(name, flag, perm)
}
打开名称为name的文件，flag是打开的方式，只读、读写等，perm是权限

 

OpenFile()这个函数有三个参数：
第一个参数表示：打开文件的路径
第二个参数表示：模式，常见的模式有
O_RDONLY(只读模式)，O_WRONLY(只写模式), O_RDWR( 可读可写模式)，O_APPEND(追加模式) os.O_TRUNC（清空模式）。

第三个参数表示:  权限，取值范围（0-7）
表示如下：
0： 没有任何权限
1： 执行权限(如果是可执行文件，是可以运行的)
2:  写权限
3:  写权限与执行权限
4： 读权限
5:  读权限与执行权限
6:  读权限与写权限
7:  读权限，写权限，执行权限

 

package main

import (
    "fmt"
    "os"
)

//OpenFile()这个函数有三个参数：
//第一个参数表示：打开文件的路径
//第二个参数表示：模式，常见的模式有
//O_RDONLY(只读模式)，O_WRONLY(只写模式), O_RDWR( 可读可写模式)，O_APPEND(追加模式)。
//
//第三个参数表示:  权限，取值范围（0-7）
//表示如下：
//0： 没有任何权限
//1： 执行权限(如果是可执行文件，是可以运行的)
//2:  写权限
//3:  写权限与执行权限
//4： 读权限
//5:  读权限与执行权限
//6:  读权限与写权限
//7:  读权限，写权限，执行权限
func main() {
    file, err := os.OpenFile("c.txt", os.O_RDWR|os.O_APPEND,6)
    if err != nil {
        fmt.Println(err)
    }
    defer file.Close()

    // 通过文件指针向文件中写入数据，读取数据
    n, err := file.WriteString("aaa")
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(n)

}

写文件

func (file *File) Write(b []byte) (n int, err error)
写入byte类型的信息到文件

func (file *File) WriteAt(b []byte, off int64) (n int, err error)
在指定位置开始写入byte类型的信息

func (f *File) WriteString(s string) (n int, err error) {
	return f.Write([]byte(s))
}
写入string信息到文件

　　

package main

import (
    "fmt"
    "os"
)

func main()  {
  file,err:=os.Create("b.txt")
  if err!=nil{
      fmt.Println(err)
  }
  defer file.Close()

  // 写入数据
  n,err:=file.WriteString("Hello World")
  if err!=nil{
      fmt.Println(err)
  }
  fmt.Println(n)

}

package main

import (
    "os"
    "fmt"
)

func main() {
    file, err := os.Create("c.txt")
    if err != nil {
        fmt.Println(err)
    }
    defer file.Close()

    var str string = "Hello World"
    n, err := file.Write([]byte(str)) // 需要将字符串转成字节切片
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(n)
    //file.WriteString()
}

package main

import (
    "fmt"
    "io"
    "os"
)

func main() {
    file, err := os.Create("d.txt")
    if err != nil {
        fmt.Println(err)
    }
    defer file.Close()
    file.WriteString("Hello World")

    var str = "aaa"
    num, _ := file.Seek(0, io.SeekEnd) // 将光标定位到文件中原有内容的后面,返回文件中原有数据的长度
    fmt.Println("num=", num)

    n, err := file.WriteAt([]byte(str), num) // 第二个参数：表示在指定位置写入数据。
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(n)

}

 

package main

import (
    "bufio"
    "fmt"
    "io"
    "os"
)

func main() {
    path := "c.txt"
    line_content := "hello\n"
    Writelines(path, line_content)
}


func Writelines(filename, content string) error {
    // 写入文件
    // 判断文件是否存在
    if _, err := os.Stat(filename); os.IsNotExist(err) {
        return err
    }
    f, err := os.OpenFile(filename, os.O_RDWR|os.O_APPEND, 6)
    defer f.Close()
    if err != nil {
        return err
    }
    w := bufio.NewWriter(f)
    _, err2 := w.WriteString(content)
    if err2 != nil {
        return err2
    }
    w.Flush()
    f.Sync()
    return nil
}

读文件

func (file *File) Read(b []byte) (n int, err Error)
读取数据到b中
它接收一个字节切片，返回读取的字节数和可能的具体错误，读到文件末尾时会返回0和io.EOF

func (file *File) ReadAt(b []byte, off int64) (n int, err Error)
从off开始读取数据到b中

　　

package main

import (
    "fmt"
    "io/ioutil"
)

// ioutil读取文件
func readFile(filename string) {
    content, err := ioutil.ReadFile(filename)
    if err != nil {
        fmt.Println("read file failed, err:", err)
        return
    }
    fmt.Print(string(content))
}

func main() {
    readFile("xx.txt")

}

package main

import (
    "os"
    "fmt"
)

func main() {
    // 1: 打开要读取的文件
    file, err := os.Open("c.txt") // 注意：OpenFile方法的区别
    if err != nil {
        fmt.Println(err)
    }
    defer file.Close()

    // 2: 进行文件内容读取
    // 定义一个字符类型切片，存储从文件中读取的数据
    buffer := make([]byte, 1024*2) // 大小为2kb
    n, err := file.Read(buffer) // 将从文件中读取的数据保存到字符切片中， n:表示从文件中读取的数据的长度
    if err != nil {
        fmt.Println(err)
    }
    fmt.Println(string(buffer[:n]))
    fmt.Println("读取数据的长度:",n)
    // 3: 关闭文件
}

 

package main

import (
    "bufio"
    "fmt"
    "io"
    "os"
)

// bufio读数据
func readByLine() {
    f, err := os.Open("xx.txt")
    if err != nil {
        fmt.Println("open file failed, err:", err)
        return
    }
    defer f.Close()
    // 利用缓冲区从文件读数据
    reader := bufio.NewReader(f)
    for {
        line, err := reader.ReadString('\n') // 字符
        if err == io.EOF {
            fmt.Print(line)
            break
        }
        if err != nil {
            fmt.Println("read file failed, err:", err)
            return
        }
        fmt.Print(line)
    }
}

func main() {
    readByLine()

}

 

删除文件

func Remove(name string) Error
调用该函数就可以删除文件名为name的文件

  

总结：bufio性能更高、且更节省内存