go标准库io、ioutil

本文主要是介绍go标准库io、ioutil，希望对大家解决编程问题提供一定的参考价值，需要的开发者们随着小编来一起学习吧！

标准库io

io. WriteString

s输出到w

func WriteString(w Writer, s string) (n int, err error)

io.Copy

自动以32k字节的buf进行遍历复制直到遇到io.EOF。返回总共复制的字节数，如果成功err返回nil

func Copy(dst Writer, src Reader) (written int64, err error) {return copyBuffer(dst, src, nil)
}

例如

func handlefunc(w http.ResponseWriter, r *http.Request)  {f, _ := os.Open("./1.txt")defer f.Close()_,err := io.Copy(w,f)errCheck(err)
}

io.CopyBuffer

比io.Copy多一项可以自定buf大小

func CopyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error) {if buf != nil && len(buf) == 0 {panic("empty buffer in io.CopyBuffer")}return copyBuffer(dst, src, buf)
}

io.CopyN

只复制前n字节，src内容足够n个字节时err返回nil，否则返回io.EOF

func CopyN(dst Writer, src Reader, n int64) (written int64, err error)

io.MultiReader

func MultiReader(readers ...Reader) Reader

	r1 := strings.NewReader("first reader ")r2 := strings.NewReader("second reader ")r3 := strings.NewReader("third reader\n")r := io.MultiReader(r1, r2, r3)if _, err := io.Copy(os.Stdout, r); err != nil {log.Fatal(err)}// Output: first reader second reader third reader

io.Multiwriter

func MultiWriter(writers ...Writer) Writer

        r := strings.NewReader("some io.Reader stream to be read\n")var buf1, buf2 bytes.Bufferw := io.MultiWriter(&buf1, &buf2)if _, err := io.Copy(w, r); err != nil {log.Fatal(err)}fmt.Print(buf1.String())fmt.Print(buf2.String())// Output:// some io.Reader stream to be read// some io.Reader stream to be read

io.pipe

读和写用channel通信，读操作阻塞直到有被写入内容

func Pipe() (*PipeReader, *PipeWriter)

        r, w := io.Pipe()go func() {fmt.Fprint(w, "some text to be read\n")w.Close()}()buf := new(bytes.Buffer)buf.ReadFrom(r)fmt.Print(buf.String())// Output: some text to be read

io.TeeReader

将w传给r的内容同样传给返回的reader

func TeeReader(r Reader, w Writer) Reader

io.NewSectionReader

从第off个字节开始读取n个字节

func NewSectionReader(r ReaderAt, off int64, n int64) *SectionReader

        r := strings.NewReader("some io.Reader stream to be read\n")s := io.NewSectionReader(r, 5, 16)buf := make([]byte, 6)if _, err := s.ReadAt(buf, 10); err != nil {  //SectionReader的方法log.Fatal(err)}fmt.Printf("%s\n", buf)// Output: stream

        r := strings.NewReader("some io.Reader stream to be read\n")if _, err := io.Copy(os.Stdout, r); err != nil {log.Fatal(err)}r.Seek(15, io.SeekStart)if _, err := io.Copy(os.Stdout, r); err != nil {log.Fatal(err)}r.Seek(-5, io.SeekEnd)if _, err := io.Copy(os.Stdout, r); err != nil {log.Fatal(err)}// Output:// some io.Reader stream to be read// stream to be read// read

其他：
至少读min个字节到buf，否则返回error: short buffer
func ReadAtLeast(r Reader, buf []byte, min int) (n int, err error)

将buf填满，否则返回error: unexpected EOF
func ReadFull(r Reader, buf []byte) (n int, err error)

返回读取传入的reader前n个字节的reader
func LimitReader(r Reader, n int64) Reader

标准库ioutil

ioutil.ReadAll

遍历增加函数内部buf容量并读取，直到把内容全部读到buf中（所以比其他方法消耗内存）

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

ioutil.ReadFile

调用readall方法直接全部读取文件内容

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

ioutil.WriteFile

写内容到文件，如果文件不存在则新建，如果存在则清空再写

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

ioutil.ReadDir

获取指定文件地址下面文件的信息

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

        f,_:= ioutil.ReadDir("./")for index,fileInfo := range f{fmt.Println(index,fileInfo.Name())}

ioutil.TempFile

在指定地址生成一个以pattern为前缀随机数为后缀的随机名字的文件。每调用一次会更新内部的随机种子。如果过程中发现生成的文件名在该地址已存在，再进行一次生成，和已存在文件名不同时才新建文件。

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

ioutil.TempDir

方法同上生成文件夹，返回生成的名字。

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

//文件夹操作content := []byte("temporary file's content")dir, err := ioutil.TempDir("", "example")if err != nil {log.Fatal(err)}defer os.RemoveAll(dir) // 文件夹不用可以删除tmpfn := filepath.Join(dir, "tmpfile")if err := ioutil.WriteFile(tmpfn, content, 0666); err != nil {log.Fatal(err)}//文件操作content := []byte("temporary file's content")tmpfile, err := ioutil.TempFile("", "example.*.txt")if err != nil {log.Fatal(err)}defer os.Remove(tmpfile.Name()) // 文件不用可以删除if _, err := tmpfile.Write(content); err != nil {tmpfile.Close()log.Fatal(err)}if err := tmpfile.Close(); err != nil {log.Fatal(err)}