Golang文件IO 一

Golang文件IO 一

文件IO编程最基本、最常用的就属读写文件操作了。ioutil包实现了一些IO实用功能，其中就包括非常简捷、好用的文件读取功能。

ioutil包有7个函数1个变量：

var Discard io.Writer = devNull(0)

func NopCloser(r io.Reader) io.ReadCloser

func ReadAll(r io.Reader) ([]byte, error)

func ReadDir(dirname string) ([]os.FileInfo, error)

func ReadFile(filename string) ([]byte, error)

func TempDir(dir, prefix string) (name string, err error)

func TempFile(dir, prefix string) (f *os.File, err error)

func WriteFile(filename string, data []byte, perm os.FileMode) error

ReadFile和WriteFile这两个函数分别实现了读文件和写文件操作，一行代码即可搞定，非常便捷。

func ReadFile(filename string) ([]byte, error)

ReadFile读取filename指定的文件，返回文件的内容。如果调用成功返回err==nil，而不是err==EOF。因为ReadFile读取整个文件，不会将Read操作遇到的EOF报告为一个错误。

func WriteFile(filename string, data []byte, perm os.FileMode) error

WriteFile将data写入到filename指定的文件。如果文件不存在，WriteFile用权限perm创建文件；如果文件存在，WriteFile函数在写之前先将文件截断。

可以搭配json包实现程序配置的读写功能。下面是一个读写数据库配置的例子。

package main

import (

    "fmt"

    "io/ioutil"

    "log"

    "encoding/json"

)

type AppConf struct{

    DriverName string `json:"driver_name"`

    SqlUser string `json:"sql_user"`

    SqlPass string `json:"sql_password"`

    SqlUrls string `json:"sql_urls"`

    SqlDB string `json:"sql_db"`

}

func main() {

    appConf := AppConf{DriverName:"mysql",

    SqlUser:"root",

    SqlPass:"password",

SqlUrls:"tcp(127.0.0.1:3306)",

SqlDB:"mydb"}

    bConf,err := json.MarshalIndent(appConf,"","\t")

    if err != nil {

        log.Fatal(err)

    }

    err = ioutil.WriteFile("app.cfg",bConf,0666)

    if err != nil {

        log.Fatal(err)

    }

    var appConf2 AppConf

    bConf,err =ioutil.ReadFile("app.cfg")

    if err != nil {

        log.Fatal(err)

    }

    err = json.Unmarshal(bConf,&appConf2)

    if err != nil {

        log.Fatal(err)

    }

    fmt.Println("appConf === appConf2",appConf==appConf2)

}

　　

运行结果如下：

生成的app.cfg内容如下：

{

    "driver_name": "mysql",

    "sql_user": "root",

    "sql_password": "password",

    "sql_urls": "tcp(127.0.0.1:3306)",

    "sql_db": "mydb"

}

　　

通常WriteFile的权限是0666。关于权限的定义，可以查看golang源码(C:\Go\src\os\types.go)

// A FileMode represents a file's mode and permission bits.

// The bits have the same definition on all systems, so that

// information about files can be moved from one system

// to another portably. Not all bits apply to all systems.

// The only required bit is ModeDir for directories.

type FileMode uint32

// The defined file mode bits are the most significant bits of the FileMode.

// The nine least-significant bits are the standard Unix rwxrwxrwx permissions.

// The values of these bits should be considered part of the public API and

// may be used in wire protocols or disk representations: they must not be

// changed, although new bits might be added.

const (

    // The single letters are the abbreviations

    // used by the String method's formatting.

    ModeDir FileMode = 1 << (32 - 1 - iota) // d: is a directory

    ModeAppend // a: append-only

    ModeExclusive // l: exclusive use

    ModeTemporary // T: temporary file; Plan 9 only

    ModeSymlink // L: symbolic link

    ModeDevice // D: device file

    ModeNamedPipe // p: named pipe (FIFO)

    ModeSocket // S: Unix domain socket

    ModeSetuid // u: setuid

    ModeSetgid // g: setgid

    ModeCharDevice // c: Unix character device, when ModeDevice is set

    ModeSticky // t: sticky

    // Mask for the type bits. For regular files, none will be set.

    ModeType = ModeDir | ModeSymlink | ModeNamedPipe | ModeSocket | ModeDevice

    ModePerm FileMode = 0777 // Unix permission bits

)

　　

FileMode在所有系统种的定义相同，与linux系统的权限定义类似，一些可取的值包括如下：

  const (

        OS_READ = 04

        OS_WRITE = 02

        OS_EX = 01

        OS_USER_SHIFT = 6

        OS_GROUP_SHIFT = 3

        OS_OTH_SHIFT = 0

        OS_USER_R = OS_READ<<OS_USER_SHIFT

        OS_USER_W = OS_WRITE<<OS_USER_SHIFT

        OS_USER_X = OS_EX<<OS_USER_SHIFT

        OS_USER_RW = OS_USER_R | OS_USER_W

        OS_USER_RWX = OS_USER_RW | OS_USER_X

        OS_GROUP_R = OS_READ<<OS_GROUP_SHIFT

        OS_GROUP_W = OS_WRITE<<OS_GROUP_SHIFT

        OS_GROUP_X = OS_EX<<OS_GROUP_SHIFT

        OS_GROUP_RW = OS_GROUP_R | OS_GROUP_W

        OS_GROUP_RWX = OS_GROUP_RW | OS_GROUP_X

        OS_OTH_R = OS_READ<<OS_OTH_SHIFT

        OS_OTH_W = OS_WRITE<<OS_OTH_SHIFT

        OS_OTH_X = OS_EX<<OS_OTH_SHIFT

        OS_OTH_RW = OS_OTH_R | OS_OTH_W

        OS_OTH_RWX = OS_OTH_RW | OS_OTH_X

        OS_ALL_R = OS_USER_R | OS_GROUP_R | OS_OTH_R

        OS_ALL_W = OS_USER_W | OS_GROUP_W | OS_OTH_W

        OS_ALL_X = OS_USER_X | OS_GROUP_X | OS_OTH_X

        OS_ALL_RW = OS_ALL_R | OS_ALL_W

        OS_ALL_RWX = OS_ALL_RW | OS_GROUP_X)

　　

WriteFile权限指定为0777，Ubuntu上执行上面的例子，查看app.cfg的详细信息

dell@dell-VirtualBox:~/mygo/src/example/ioutil$ ll app.cfg

-rwxrwxr-x  dell dell  11月  : app.cfg*

WriteFile 权限指定为0666，Ubuntu上执行上面的例子，查看app.cfg的详细信息

dell@dell-VirtualBox:~/mygo/src/example/ioutil$ ll app.cfg

-rw-rw-r--  dell dell  11月  : app.cfg