io操作

io操作使用例子

package main

import (
    "bytes"
    "fmt"
    "io"
    "io/ioutil"
    "log"
    "os"
    "strings"
)

func ExampleCopy() {
    r := strings.NewReader("some io.Reader stream to be read\n")

    if _, err := io.Copy(os.Stdout, r); err != nil {
        log.Fatal(err)
    }

    // Output:
    // some io.Reader stream to be read
}

func ExampleCopyBuffer() {
    r1 := strings.NewReader("first reader\n")
    r2 := strings.NewReader("second reader\n")
    buf := make([]byte, 8)

    // buf is used here...
    if _, err := io.CopyBuffer(os.Stdout, r1, buf); err != nil {
        log.Fatal(err)
    }

    // ... reused here also. No need to allocate an extra buffer.
    if _, err := io.CopyBuffer(os.Stdout, r2, buf); err != nil {
        log.Fatal(err)
    }

    // Output:
    // first reader
    // second reader
}

func ExampleCopyN() {
    r := strings.NewReader("some io.Reader stream to be read")

    if _, err := io.CopyN(os.Stdout, r, 5); err != nil {
        log.Fatal(err)
    }

    // Output:
    // some
}

func ExampleReadAtLeast() {
    r := strings.NewReader("some io.Reader stream to be read\n")

    buf := make([]byte, 33)
    if _, err := io.ReadAtLeast(r, buf, 4); err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%s\n", buf)

    // buffer smaller than minimal read size.
    shortBuf := make([]byte, 3)
    if _, err := io.ReadAtLeast(r, shortBuf, 4); err != nil {
        fmt.Println("error:", err)
    }

    // minimal read size bigger than io.Reader stream
    longBuf := make([]byte, 64)
    if _, err := io.ReadAtLeast(r, longBuf, 64); err != nil {
        fmt.Println("error:", err)
    }

    // Output:
    // some io.Reader stream to be read
    //
    // error: short buffer
    // error: EOF
}

func ExampleReadFull() {
    r := strings.NewReader("some io.Reader stream to be read\n")

    buf := make([]byte, 4)
    if _, err := io.ReadFull(r, buf); err != nil {
        log.Fatal(err)
    }
    fmt.Printf("%s\n", buf)

    // minimal read size bigger than io.Reader stream
    longBuf := make([]byte, 64)
    if _, err := io.ReadFull(r, longBuf); err != nil {
        fmt.Println("error:", err)
    }

    // Output:
    // some
    // error: unexpected EOF
}

func ExampleWriteString() {
    io.WriteString(os.Stdout, "Hello World")

    // Output: Hello World
}

func ExampleLimitReader() {
    r := strings.NewReader("some io.Reader stream to be read\n")
    lr := io.LimitReader(r, 4)

    if _, err := io.Copy(os.Stdout, lr); err != nil {
        log.Fatal(err)
    }

    // Output:
    // some
}

func ExampleMultiReader() {
    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
}

func ExampleTeeReader() {
    r := strings.NewReader("some io.Reader stream to be read\n")
    var buf bytes.Buffer
    tee := io.TeeReader(r, &buf)

    printall := func(r io.Reader) {
        b, err := ioutil.ReadAll(r)
        if err != nil {
            log.Fatal(err)
        }

        fmt.Printf("%s", b)
    }

    printall(tee)
    printall(&buf)

    // Output:
    // some io.Reader stream to be read
    // some io.Reader stream to be read
}

func ExampleSectionReader() {
    r := strings.NewReader("some io.Reader stream to be read\n")
    s := io.NewSectionReader(r, 5, 17)

    if _, err := io.Copy(os.Stdout, s); err != nil {
        log.Fatal(err)
    }

    // Output:
    // io.Reader stream
}

func ExampleSectionReader_ReadAt() {
    r := strings.NewReader("some io.Reader stream to be read\n")
    s := io.NewSectionReader(r, 5, 16)

    fmt.Println("-----")
    if _, err := io.Copy(os.Stdout, s); err != nil {
        log.Fatal(err)
    }
    fmt.Println()

    buf := make([]byte, 6)
    if _, err := s.ReadAt(buf, 10); err != nil {
        log.Fatal(err)
    }

    fmt.Printf("%s\n", buf)

    // Output:
    // stream
}

func ExampleSectionReader_Seek() {
    r := strings.NewReader("some io.Reader stream to be read\n")
    s := io.NewSectionReader(r, 5, 16)

    if _, err := s.Seek(10, io.SeekStart); err != nil {
        log.Fatal(err)
    }

    buf := make([]byte, 6)
    if _, err := s.Read(buf); err != nil {
        log.Fatal(err)
    }

    fmt.Printf("%s\n", buf)

    // Output:
    // stream
}

func ExampleSeeker_Seek() {
    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
}

func ExampleMultiWriter() {
    r := strings.NewReader("some io.Reader stream to be read\n")

    var buf1, buf2 bytes.Buffer
    w := 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
}

func main() {
    ExampleCopy()
    ExampleCopyBuffer()
    ExampleCopyN()
    ExampleReadAtLeast()
    ExampleReadFull()
    ExampleWriteString()
    fmt.Println()
    ExampleLimitReader()
    ExampleMultiReader()
    ExampleTeeReader()
    ExampleSectionReader()
    fmt.Println()
    ExampleSectionReader_ReadAt()
    ExampleSeeker_Seek()
    ExampleMultiWriter()
}

执行结果：
some io.Reader stream to be read

first reader

second reader

some some io.Reader stream to be read

error: short buffer

error: EOF

some

error: unexpected EOF

Hello World

somefirst reader second reader third reader

some io.Reader stream to be read

some io.Reader stream to be read

io.Reader stream

-----

io.Reader stream

stream

some io.Reader stream to be read

stream to be read

read

some io.Reader stream to be read

some io.Reader stream to be read

成功: 进程退出代码 0.