Golang丰富的I/O----用N种Hello World展示
Golang是我目前用过的最好的语言，一接触便深深地喜爱，不断实践，喜爱之情日久弥深。原因之一便是简单、强大、易用。编程操作涉及频率最高的莫过于I/O，标准io包提供的两个接口（io.Reader和io.Writer）对I/O进行了伟大的统一抽象，将简单、强大、易用的特点体现地淋漓尽致。两个接口的定义如下：
typeReaderinterface {
Read(p []byte) (n int, err error)
}
typeWriterinterface {
Write(p []byte) (n int, err error)
}
标准库中的多个包实现了这两个接口，从而提供了丰富而强大的I/O功能。下面用N种输出“Hello，world!”来感受下。
package main
import (
"bufio"
"bytes"
"fmt"
"io"
"log"
"mime/quotedprintable"
"os"
"strings"
"text/tabwriter"
)
func main() {
//1
fmt.Println("hello, world!")
//2
io.WriteString(os.Stdout, "Hello, World!\r\n")
os.Stdout.WriteString("Hello, World!\r\n")
//3
w := bufio.NewWriter(os.Stdout)
fmt.Fprint(w, "Hello, ")
fmt.Fprint(w, "world!\r\n")
w.Flush() // Don't forget to flush!
fmt.Fprint(os.Stdout, "hello, world!\r\n")
//4
r := strings.NewReader("hello, world!\r\n")
if _, err := io.Copy(os.Stdout, r); err != nil {
log.Fatal(err)
}
r1 := strings.NewReader("hello, world!\r\n")
buf := make([]byte, 8)
// buf is used here...
if _, err := io.CopyBuffer(os.Stdout, r1, buf); err != nil {
log.Fatal(err)
}
r2 := strings.NewReader("hello, world!\r\n")
//buf := make([]byte, 8)
if _, err := io.CopyN(os.Stdout, r2, int64(r2.Len())); err != nil {
log.Fatal(err)
}
//5
var b bytes.Buffer // A Buffer needs no initialization.
b.Write([]byte("Hello, "))
fmt.Fprintf(&b, "world!\r\n")
b.WriteTo(os.Stdout)
// Output: Hello world!
//6
wTab := tabwriter.NewWriter(os.Stdout, 1, 1, 1, ' ', tabwriter.AlignRight)
defer wTab.Flush()
wTab.Write([]byte("Hello, world!\r\n"))
//7
wQuote := quotedprintable.NewWriter(os.Stdout)
wQuote.Write([]byte("Hello, world!\r\n"))
wQuote.Write([]byte("These symbols will be escaped: = \t"))
wQuote.Close()
wQuote.Write([]byte("\r\n"))
//8
log := log.New(os.Stdout, "", 0)
log.Println("Hello, world!")
}
以上代码均来自go源码，编译运行输出如下：
hello, world! Hello, World! Hello, World! Hello, world! hello, world! hello, world! hello, world! hello, world! Hello, world! Hello, world! Hello, world! These symbols will be escaped: =3D =09 Hello, world!
第一种很常见，
fmt.Println("hello, world!")
各种go语言书籍中均展示了该种形式的Hello World。
第二种是io包和os包提供的WriteString函数或方法，对io.Writer进行了封装。
第三种是fmt包提供的Fprint函数，与第一种类似。从go源码可以看出Print和Println分别是对Fprint和Fprintln函数的封装。
func Print(a ...interface{}) (n int, err error) {
return Fprint(os.Stdout, a...)
}
func Println(a ...interface{}) (n int, err error) {
return Fprintln(os.Stdout, a...)
}
第四种是io包提供的三个copy函数：io.Copy、io.CopyBuffer和io.CopyN。这三个函数是对copyBuffer函数的封装，
// copyBuffer is the actual implementation of Copy and CopyBuffer. // if buf is nil, one is allocated. func copyBuffer(dst Writer, src Reader, buf []byte) (written int64, err error)
copyBuffer函数借助buf缓冲从Reader读取数据然后写入到Writer中。
第五种是bytes包提供的方法，对Writer方法进行了封装。
// WriteTo writes data to w until the buffer is drained or an error occurs. // The return value n is the number of bytes written; it always fits into an // int, but it is int64 to match the io.WriterTo interface. Any error // encountered during the write is also returned. func (b *Buffer) WriteTo(w io.Writer) (n int64, err error)
第六种是text包实现的io.Writer接口，text/tabwriter包可以实现文本列对齐输出。
// Write writes buf to the writer b.
// The only errors returned are ones encountered
// while writing to the underlying output stream.
//
func (b *Writer) Write(buf []byte) (n int, err error) {
第七种是"mime/quotedprintable"包实现的io.Writer接口。
// Write encodes p using quoted-printable encoding and writes it to the
// underlying io.Writer. It limits line length to 76 characters. The encoded
// bytes are not necessarily flushed until the Writer is closed.
func (w *Writer) Write(p []byte) (n int, err error) {
第八种也是比较常用的，由log包提供的。
这么多种Hello World的写法可能不是全面的，但这是我见过的写法最多的一种语言。
