Golang read and write file operations
1, read file
Use golang default language to read a file will be a variety of ways, here we introduce the following.
Use ioutil read directly
need to introduce io / ioutil package, which by default has the following functions for users to call.
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) errorRead the file, we can see the following three functions:
//从一个io.Reader类型中读取内容直到返回错误或者EOF时返回读取的数据，当err == nil时，数据成功读取到[]byte中
//ReadAll函数被定义为从源中读取数据直到EOF，它是不会去从返回数据中去判断EOF来作为读取成功的依据
func ReadAll(r io.Reader) ([]byte, error)
//读取一个目录，并返回一个当前目录下的文件对象列表和错误信息
func ReadDir(dirname string) ([]os.FileInfo, error)
//读取文件内容，并返回[]byte数据和错误信息。err == nil时，读取成功
func ReadFile(filename string) ([]byte, error)Read the file:
package main
import (
"fmt"
"io/ioutil"
"strings"
)
func main() {
Ioutil("mytestfile.txt")
}
func Ioutil(name string) {
if contents,err := ioutil.ReadFile(name);err == nil {
//因为contents是[]byte类型，直接转换成string类型后会多一行空格,需要使用strings.Replace替换换行符
result := strings.Replace(string(contents),"\n","",1)
fmt.Println(result)
}
}
$ go run readfile.go
xxbandy.github.io @by Andy_xuMeans os.Openfor reading file
since a file is to open os.Open and returns a file object, in fact, may be combined so ioutil.ReadAll (r io.Reader) for reading. io.Reader is actually a type of interface that contains the Read method, and the file object is to achieve a Read method.
We first look at the correlation function os.Open family
//打开一个需要被读取的文件，如果成功读取，返回的文件对象将可用被读取，该函数默认的权限为O_RDONLY，也就是只对文件有只读权限。如果有错误，将返回*PathError类型
func Open(name string) (*File, error)
//大部分用户会选择该函数来代替Open or Create函数。该函数主要用来指定参数(os.O_APPEND|os.O_CREATE|os.O_WRONLY)以及文件权限(0666)来打开文件，如果打开成功返回的文件对象将被用作I/O操作
func OpenFile(name string, flag int, perm FileMode) (*File, error)Use os.Open family function and ioutil.ReadAll () reads file example:
func OsIoutil(name string) {
if fileObj,err := os.Open(name);err == nil {
//if fileObj,err := os.OpenFile(name,os.O_RDONLY,0644); err == nil {
defer fileObj.Close()
if contents,err := ioutil.ReadAll(fileObj); err == nil {
result := strings.Replace(string(contents),"\n","",1)
fmt.Println("Use os.Open family functions and ioutil.ReadAll to read a file contents:",result)
}
}
}
# 在main函数中调用OsIoutil(name)函数就可以读取文件内容了However, some of the above would be more complicated, because of the use os the same time with the ioutil, but when reading large files is quite advantageous. But reading small files can use some method of file objects directly.
Whether or os.OpenFile said above os.Open they eventually returns a file object * File, which is the default file object There are many ways in which to read the file methods as follows:
//从文件对象中读取长度为b的字节，返回当前读到的字节数以及错误信息。因此使用该方法需要先初始化一个符合内容大小的空的字节列表。读取到文件的末尾时，该方法返回0，io.EOF
func (f *File) Read(b []byte) (n int, err error)
//从文件的off偏移量开始读取长度为b的字节。返回读取到字节数以及错误信息。当读取到的字节数n小于想要读取字节的长度len(b)的时候，该方法将返回非空的error。当读到文件末尾时，err返回io.EOF
func (f *File) ReadAt(b []byte, off int64) (n int, err error)Use the Read method to read the file object:
func FileRead(name string) {
if fileObj,err := os.Open(name);err == nil {
defer fileObj.Close()
//在定义空的byte列表时尽量大一些，否则这种方式读取内容可能造成文件读取不完整
buf := make([]byte, 1024)
if n,err := fileObj.Read(buf);err == nil {
fmt.Println("The number of bytes read:"+strconv.Itoa(n),"Buf length:"+strconv.Itoa(len(buf)))
result := strings.Replace(string(buf),"\n","",1)
fmt.Println("Use os.Open and File's Read method to read a file:",result)
}
}
}Use os.Open read the file contents and bufio.Reader
bufio package implements the cache IO, it wraps itself around the io.Reader and io.Writer object, creating additional Reader and Writer objects, but that way is with a cache, so for text I / O for the package It is to provide some handy.
Look at the correlation function method in bufio Reader Module:
//首先定义了一个用来缓冲io.Reader对象的结构体，同时该结构体拥有以下相关的方法
type Reader struct {
}
//NewReader函数用来返回一个默认大小buffer的Reader对象(默认大小好像是4096) 等同于NewReaderSize(rd,4096)
func NewReader(rd io.Reader) *Reader
//该函数返回一个指定大小buffer(size最小为16)的Reader对象，如果 io.Reader参数已经是一个足够大的Reader，它将返回该Reader
func NewReaderSize(rd io.Reader, size int) *Reader
//该方法返回从当前buffer中能被读到的字节数
func (b *Reader) Buffered() int
//Discard方法跳过后续的 n 个字节的数据，返回跳过的字节数。如果0 <= n <= b.Buffered(),该方法将不会从io.Reader中成功读取数据。
func (b *Reader) Discard(n int) (discarded int, err error)
//Peekf方法返回缓存的一个切片，该切片只包含缓存中的前n个字节的数据
func (b *Reader) Peek(n int) ([]byte, error)
//把Reader缓存对象中的数据读入到[]byte类型的p中，并返回读取的字节数。读取成功，err将返回空值
func (b *Reader) Read(p []byte) (n int, err error)
//返回单个字节，如果没有数据返回err
func (b *Reader) ReadByte() (byte, error)
//该方法在b中读取delimz之前的所有数据，返回的切片是已读出的数据的引用，切片中的数据在下一次的读取操作之前是有效的。如果未找到delim，将返回查找结果并返回nil空值。因为缓存的数据可能被下一次的读写操作修改，因此一般使用ReadBytes或者ReadString，他们返回的都是数据拷贝
func (b *Reader) ReadSlice(delim byte) (line []byte, err error)
//功能同ReadSlice，返回数据的拷贝
func (b *Reader) ReadBytes(delim byte) ([]byte, error)
//功能同ReadBytes,返回字符串
func (b *Reader) ReadString(delim byte) (string, error)
//该方法是一个低水平的读取方式，一般建议使用ReadBytes('\n') 或 ReadString('\n')，或者使用一个 Scanner来代替。ReadLine 通过调用 ReadSlice 方法实现，返回的也是缓存的切片，用于读取一行数据，不包括行尾标记（\n 或 \r\n）
func (b *Reader) ReadLine() (line []byte, isPrefix bool, err error)
//读取单个UTF-8字符并返回一个rune和字节大小
func (b *Reader) ReadRune() (r rune, size int, err error)
Examples are as follows:
func BufioRead(name string) {
if fileObj,err := os.Open(name);err == nil {
defer fileObj.Close()
//一个文件对象本身是实现了io.Reader的 使用bufio.NewReader去初始化一个Reader对象，存在buffer中的，读取一次就会被清空
reader := bufio.NewReader(fileObj)
//使用ReadString(delim byte)来读取delim以及之前的数据并返回相关的字符串.
if result,err := reader.ReadString(byte('@'));err == nil {
fmt.Println("使用ReadSlince相关方法读取内容:",result)
}
//注意:上述ReadString已经将buffer中的数据读取出来了，下面将不会输出内容
//需要注意的是，因为是将文件内容读取到[]byte中，因此需要对大小进行一定的把控
buf := make([]byte,1024)
//读取Reader对象中的内容到[]byte类型的buf中
if n,err := reader.Read(buf); err == nil {
fmt.Println("The number of bytes read:"+strconv.Itoa(n))
//这里的buf是一个[]byte，因此如果需要只输出内容，仍然需要将文件内容的换行符替换掉
fmt.Println("Use bufio.NewReader and os.Open read file contents to a []byte:",string(buf))
}
}
}Reading all the documents by way of example:
package main
import (
"fmt"
"io/ioutil"
"strings"
"os"
"strconv"
"bufio"
)
func main() {
Ioutil("mytestfile.txt")
OsIoutil("mytestfile.txt")
FileRead("mytestfile.txt")
BufioRead("mytestfile.txt")
}
func Ioutil(name string) {
if contents,err := ioutil.ReadFile(name);err == nil {
//因为contents是[]byte类型，直接转换成string类型后会多一行空格,需要使用strings.Replace替换换行符
result := strings.Replace(string(contents),"\n","",1)
fmt.Println("Use ioutil.ReadFile to read a file:",result)
}
}
func OsIoutil(name string) {
if fileObj,err := os.Open(name);err == nil {
//if fileObj,err := os.OpenFile(name,os.O_RDONLY,0644); err == nil {
defer fileObj.Close()
if contents,err := ioutil.ReadAll(fileObj); err == nil {
result := strings.Replace(string(contents),"\n","",1)
fmt.Println("Use os.Open family functions and ioutil.ReadAll to read a file :",result)
}
}
}
func FileRead(name string) {
if fileObj,err := os.Open(name);err == nil {
defer fileObj.Close()
//在定义空的byte列表时尽量大一些，否则这种方式读取内容可能造成文件读取不完整
buf := make([]byte, 1024)
if n,err := fileObj.Read(buf);err == nil {
fmt.Println("The number of bytes read:"+strconv.Itoa(n),"Buf length:"+strconv.Itoa(len(buf)))
result := strings.Replace(string(buf),"\n","",1)
fmt.Println("Use os.Open and File's Read method to read a file:",result)
}
}
}
func BufioRead(name string) {
if fileObj,err := os.Open(name);err == nil {
defer fileObj.Close()
//一个文件对象本身是实现了io.Reader的 使用bufio.NewReader去初始化一个Reader对象，存在buffer中的，读取一次就会被清空
reader := bufio.NewReader(fileObj)
//使用ReadString(delim byte)来读取delim以及之前的数据并返回相关的字符串.
if result,err := reader.ReadString(byte('@'));err == nil {
fmt.Println("使用ReadSlince相关方法读取内容:",result)
}
//注意:上述ReadString已经将buffer中的数据读取出来了，下面将不会输出内容
//需要注意的是，因为是将文件内容读取到[]byte中，因此需要对大小进行一定的把控
buf := make([]byte,1024)
//读取Reader对象中的内容到[]byte类型的buf中
if n,err := reader.Read(buf); err == nil {
fmt.Println("The number of bytes read:"+strconv.Itoa(n))
//这里的buf是一个[]byte，因此如果需要只输出内容，仍然需要将文件内容的换行符替换掉
fmt.Println("Use bufio.NewReader and os.Open read file contents to a []byte:",string(buf))
}
}
}Write file
Then the above method of ways to read the file way supports writing files, related as follows:
Use ioutil package file write
// 写入[]byte类型的data到filename文件中，文件权限为perm
func WriteFile(filename string, data []byte, perm os.FileMode) errorpackage main
import "io/ioutil"
/*
文件操作
*/
func main() {
s := "你好啊！"
x := []byte(s)
WriteFile("1.txt", x)
}
func WriteFile(fileName string, b []byte) {
err := ioutil.WriteFile(fileName, b, 0666)
if err != nil {
println("err", err)
}
}
Use os.Open correlation function file write
Because the function os.Open series opens the file and returns a file object, and the object is a file structure of a defined, has written a number of related methods.
Object file written to the file structure and related method:
//写入长度为b字节切片到文件f中，返回写入字节号和错误信息。当n不等于len(b)时，将返回非空的err
func (f *File) Write(b []byte) (n int, err error)
//在off偏移量出向文件f写入长度为b的字节
func (f *File) WriteAt(b []byte, off int64) (n int, err error)
//类似于Write方法，但是写入内容是字符串而不是字节切片
func (f *File) WriteString(s string) (n int, err error)Note: Use WriteString () j found it impossible to write files cover all new content frequently normal when new content is written. (Because the string length is not the same as)
Example:
//使用os.OpenFile()相关函数打开文件对象，并使用文件对象的相关方法进行文件写入操作
func WriteWithFileWrite(name,content string){
fileObj,err := os.OpenFile(name,os.O_RDWR|os.O_CREATE|os.O_TRUNC,0644)
if err != nil {
fmt.Println("Failed to open the file",err.Error())
os.Exit(2)
}
defer fileObj.Close()
if _,err := fileObj.WriteString(content);err == nil {
fmt.Println("Successful writing to the file with os.OpenFile and *File.WriteString method.",content)
}
contents := []byte(content)
if _,err := fileObj.Write(contents);err == nil {
fmt.Println("Successful writing to thr file with os.OpenFile and *File.Write method.",content)
}
}Note: Use os.OpenFile (name string, flag int, perm FileMode) Open a file and the file content changes, you need to pay attention to flag the relevant parameters and meaning.
const (
O_RDONLY int = syscall.O_RDONLY // 只读打开文件和os.Open()同义
O_WRONLY int = syscall.O_WRONLY // 只写打开文件
O_RDWR int = syscall.O_RDWR // 读写方式打开文件
O_APPEND int = syscall.O_APPEND // 当写的时候使用追加模式到文件末尾
O_CREATE int = syscall.O_CREAT // 如果文件不存在，此案创建
O_EXCL int = syscall.O_EXCL // 和O_CREATE一起使用, 只有当文件不存在时才创建
O_SYNC int = syscall.O_SYNC // 以同步I/O方式打开文件，直接写入硬盘.
O_TRUNC int = syscall.O_TRUNC // 如果可以的话，当打开文件时先清空文件
)Io package using the correlation function written to the file
has a WriteString () function to write a string object in Writer io package.
//将字符串s写入w(可以是一个[]byte)，如果w实现了一个WriteString方法，它可以被直接调用。否则w.Write会再一次被调用
func WriteString(w Writer, s string) (n int, err error)
//Writer对象的定义
type Writer interface {
Write(p []byte) (n int, err error)
}
Example:
//使用io.WriteString()函数进行数据的写入
func WriteWithIo(name,content string) {
fileObj,err := os.OpenFile(name,os.O_RDWR|os.O_CREATE|os.O_APPEND,0644)
if err != nil {
fmt.Println("Failed to open the file",err.Error())
os.Exit(2)
}
if _,err := io.WriteString(fileObj,content);err == nil {
fmt.Println("Successful appending to the file with os.OpenFile and io.WriteString.",content)
}
}Bufio package using the correlation function written to the file
io package bufio and many operations are similar, the only difference is bufio provides some cushion operation, if the file I / O operation is relatively frequent use bufio can still add some performance.
In bufio package, there is a Writer structure, and its associated methods to support a number of write operations.
//Writer是一个空的结构体，一般需要使用NewWriter或者NewWriterSize来初始化一个结构体对象
type Writer struct {
// contains filtered or unexported fields
}
//NewWriterSize和NewWriter函数
//返回默认缓冲大小的Writer对象(默认是4096)
func NewWriter(w io.Writer) *Writer
//指定缓冲大小创建一个Writer对象
func NewWriterSize(w io.Writer, size int) *Writer
//Writer对象相关的写入数据的方法
//把p中的内容写入buffer,返回写入的字节数和错误信息。如果nn<len(p),返回错误信息中会包含为什么写入的数据比较短
func (b *Writer) Write(p []byte) (nn int, err error)
//将buffer中的数据写入 io.Writer
func (b *Writer) Flush() error
//以下三个方法可以直接写入到文件中
//写入单个字节
func (b *Writer) WriteByte(c byte) error
//写入单个Unicode指针返回写入字节数错误信息
func (b *Writer) WriteRune(r rune) (size int, err error)
//写入字符串并返回写入字节数和错误信息
func (b *Writer) WriteString(s string) (int, error)
Note: If you need to use a buffer, then written to the file only using the Write method bufio package
Example:
//使用bufio包中Writer对象的相关方法进行数据的写入
func WriteWithBufio(name,content string) {
if fileObj,err := os.OpenFile(name,os.O_RDWR|os.O_CREATE|os.O_APPEND,0644);err == nil {
defer fileObj.Close()
writeObj := bufio.NewWriterSize(fileObj,4096)
//
if _,err := writeObj.WriteString(content);err == nil {
fmt.Println("Successful appending buffer and flush to file with bufio's Writer obj WriteString method",content)
}
//使用Write方法,需要使用Writer对象的Flush方法将buffer中的数据刷到磁盘
buf := []byte(content)
if _,err := writeObj.Write(buf);err == nil {
fmt.Println("Successful appending to the buffer with os.OpenFile and bufio's Writer obj Write method.",content)
if err := writeObj.Flush(); err != nil {panic(err)}
fmt.Println("Successful flush the buffer data to file ",content)
}
}
}
Writing papers are all examples
package main
import (
"os"
"io"
"fmt"
"io/ioutil"
"bufio"
)
func main() {
name := "testwritefile.txt"
content := "Hello, xxbandy.github.io!\n"
WriteWithIoutil(name,content)
contents := "Hello, xuxuebiao\n"
//清空一次文件并写入两行contents
WriteWithFileWrite(name,contents)
WriteWithIo(name,content)
//使用bufio包需要将数据先读到buffer中，然后在flash到磁盘中
WriteWithBufio(name,contents)
}
//使用ioutil.WriteFile方式写入文件,是将[]byte内容写入文件,如果content字符串中没有换行符的话，默认就不会有换行符
func WriteWithIoutil(name,content string) {
data := []byte(content)
if ioutil.WriteFile(name,data,0644) == nil {
fmt.Println("写入文件成功:",content)
}
}
//使用os.OpenFile()相关函数打开文件对象，并使用文件对象的相关方法进行文件写入操作
//清空一次文件
func WriteWithFileWrite(name,content string){
fileObj,err := os.OpenFile(name,os.O_RDWR|os.O_CREATE|os.O_TRUNC,0644)
if err != nil {
fmt.Println("Failed to open the file",err.Error())
os.Exit(2)
}
defer fileObj.Close()
if _,err := fileObj.WriteString(content);err == nil {
fmt.Println("Successful writing to the file with os.OpenFile and *File.WriteString method.",content)
}
contents := []byte(content)
if _,err := fileObj.Write(contents);err == nil {
fmt.Println("Successful writing to thr file with os.OpenFile and *File.Write method.",content)
}
}
//使用io.WriteString()函数进行数据的写入
func WriteWithIo(name,content string) {
fileObj,err := os.OpenFile(name,os.O_RDWR|os.O_CREATE|os.O_APPEND,0644)
if err != nil {
fmt.Println("Failed to open the file",err.Error())
os.Exit(2)
}
if _,err := io.WriteString(fileObj,content);err == nil {
fmt.Println("Successful appending to the file with os.OpenFile and io.WriteString.",content)
}
}
//使用bufio包中Writer对象的相关方法进行数据的写入
func WriteWithBufio(name,content string) {
if fileObj,err := os.OpenFile(name,os.O_RDWR|os.O_CREATE|os.O_APPEND,0644);err == nil {
defer fileObj.Close()
writeObj := bufio.NewWriterSize(fileObj,4096)
//
if _,err := writeObj.WriteString(content);err == nil {
fmt.Println("Successful appending buffer and flush to file with bufio's Writer obj WriteString method",content)
}
//使用Write方法,需要使用Writer对象的Flush方法将buffer中的数据刷到磁盘
buf := []byte(content)
if _,err := writeObj.Write(buf);err == nil {
fmt.Println("Successful appending to the buffer with os.OpenFile and bufio's Writer obj Write method.",content)
if err := writeObj.Flush(); err != nil {panic(err)}
fmt.Println("Successful flush the buffer data to file ",content)
}
}
}Additional file
package main
import (
"os"
"strings"
"time"
)
/*
文件操作
*/
func main() {
AppendFile("nihao")
}
func AppendFile(str_content string) {
fd, _ := os.OpenFile("a.txt", os.O_RDWR|os.O_CREATE|os.O_APPEND, 0644)
fd_time := time.Now().Format("2006-01-02 15:04:05")
fd_content := strings.Join([]string{"======", fd_time, "=====", str_content, "\n"}, "")
buf := []byte(fd_content)
fd.Write(buf)
fd.Close()
}