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。
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