golang中的print系函数详解

pirnt系函数来自fmt包，主要用于做各种格式的输出
这些函数主要有

1. fmt.Fprintf
2. fmt.Printf
3. fmt.Sprintf
4. fmt.Fprint
5. fmt.Print
6. fmt.Sprint
7. fmt.Fprintln
8. fmt.Println
9. fmt.Sprintln
10. 总结

下面来逐个分析

import (
    "fmt"
    "os"
    "io"
)

• 函数原型：

Fprintf(w io.Writer, format string, a ...interface{}) (n int, err error)

• 官方注释
  Fprintf formats according to a format specifier and writes to w.It returns the number of bytes written and any write error encountered.

• Arguement
  fmt.Fprintf()依据指定的格式向第一个参数内写入字符串，第一参数必须实现了 io.Writer接口。Fprintf()能够写入任何类型，只要其实现了 Write方法，包括 os.Stdout,文件（例如 os.File），管道，网络连接，通道等等，同样的也可以使用 bufio包中缓冲写入。bufio 包中定义了 type Writer struct{...}。Fprintf：来格式化并输出到 io.Writers 而不是 os.Stdout。

// example
func ExampleFprintf() {
	const name, age = "Kim", 22
	n, err := fmt.Fprintf(os.Stdout, "%s is %d years old.n", name, age)

	// The n and err return values from Fprintf are
	// those returned by the underlying io.Writer.
	if err != nil {
		fmt.Fprintf(os.Stderr, "Fprintf: %vn", err)
	}
	fmt.Printf("%d bytes written.n", n)

	// Output:
	// Kim is 22 years old.
	// 21 bytes written.
}
ExampleFprintf()

Kim is 22 years old.
21 bytes written.

• 函数原型

Printf(format string, a ...interface{}) (n int, err error)

• 官方注释
  Printf formats according to a format specifier and writes to standard output.It returns the number of bytes written and any write error encountered.

• Arguement
  只可以打印出格式化的字符串。只可以直接输出字符串类型的变量（不可以输出整形变量和整形 等），其实这个函数是fmt.Fprintf的调用，其调用语句return Fprintf(os.Stdout, format, a...)，输出对象为标准输出。

• optional

fmt.Printf("整数：%dt浮点数：%vt字符串：%sn", 1, 3.14, "hello world")
func ExamplePrintf() {
	const name, age = "Kim", 22
	fmt.Printf("%s is %d years old.n", name, age)

	// It is conventional not to worry about any
	// error returned by Printf.

	// Output:
	// Kim is 22 years old.
}
ExamplePrintf()

整数：1	浮点数：3.14	字符串：hello world
Kim is 22 years old.

• 函数原型

func Sprintf(format string, a ...interface{}) string

• 官方注释
  Sprintf formats according to a format specifier and returns the resulting string.

• Argument
  格式化并返回一个字符串而不带任何输出。可用于给其他函数传递格式化参数。

func ExampleSprintf() {
	const name, age = "Kim", 22
	s := fmt.Sprintf("%s is %d years old.n", name, age)

	io.WriteString(os.Stdout, s) // Ignoring error for simplicity.

	// Output:
	// Kim is 22 years old.
}
ExampleSprintf()

Kim is 22 years old.

• 函数原型

Fprint(w io.Writer, a ...interface{}) (n int, err error)

• 官方注释
  Fprint formats using the default formats for its operands and writes to w.Spaces are added between operands when neither is a string.It returns the number of bytes written and any write error encountered.

• Argument
  向io.Writer对象中输入字符，第一个参数为输入对象，后面的参数为字符串，直接输出

func ExampleFprint() {
	const name, age = "Kim", 22
	n, err := fmt.Fprint(os.Stdout, name, " is ", age, " years old.n")

	// The n and err return values from Fprint are
	// those returned by the underlying io.Writer.
	if err != nil {
		fmt.Fprintf(os.Stderr, "Fprint: %vn", err)
	}
	fmt.Print(n, " bytes written.n")

	// Output:
	// Kim is 22 years old.
	// 21 bytes written.
}
ExampleFprint()

Kim is 22 years old.
21 bytes written.

• 函数原型

func Print(a ...interface{}) (n int, err error) {
	return Fprint(os.Stdout, a...)
}

• 官方注释
  Print formats using the default formats for its operands and writes to standard output.Spaces are added between operands when neither is a string.It returns the number of bytes written and any write error encountered.

• Arguement
  显然，这个函数是对fmt.Fprint的调用，只是把输入对象默认为标准输出。

func ExamplePrint() {
	const name, age = "Kim", 22
	fmt.Print(name, " is ", age, " years old.n")

	// It is conventional not to worry about any
	// error returned by Print.

	// Output:
	// Kim is 22 years old.
}
ExamplePrint()

Kim is 22 years old.

• 函数原型

Sprint(a ...interface{}) string  

• 官方注释
  Sprint formats using the default formats for its operands and returns the resulting string.Spaces are added between operands when neither is a string.

• Arguement
  格式化并返回一个字符串而不带任何输出

func ExampleSprint() {
	const name, age = "Kim", 22
	s := fmt.Sprint(name, " is ", age, " years old.n")

	io.WriteString(os.Stdout, s) // Ignoring error for simplicity.

	// Output:
	// Kim is 22 years old.
}
ExampleSprint()

Kim is 22 years old.

• 函数原型

Fprintln(w io.Writer, a ...interface{}) (n int, err error)

• 官方注释
  Fprintln formats using the default formats for its operands and writes to w.Spaces are always added between operands and a newline is appended.It returns the number of bytes written and any write error encountered.

• Arguement
  输入字符串到io.Writer,并且带有换行

func ExampleFprintln() {
	const name, age = "Kim", 22
	n, err := fmt.Fprintln(os.Stdout, name, "is", age, "years old.")

	// The n and err return values from Fprintln are
	// those returned by the underlying io.Writer.
	if err != nil {
		fmt.Fprintf(os.Stderr, "Fprintln: %vn", err)
	}
	fmt.Println(n, "bytes written.")

	// Output:
	// Kim is 22 years old.
	// 21 bytes written.
}
ExampleFprintln()

Kim is 22 years old.
21 bytes written.

• 函数原型

func Println(a ...interface{}) (n int, err error) {
	return Fprintln(os.Stdout, a...)
}

• 官方注释
  Println formats using the default formats for its operands and writes to standard output.Spaces are always added between operands and a newline is appended.It returns the number of bytes written and any write error encountered.

• Arguement
  显然这个函数是对fmt.Fprintln的调用，输入到os.Stdout

func ExamplePrintln() {
	const name, age = "Kim", 22
	fmt.Println(name, "is", age, "years old.")

	// It is conventional not to worry about any
	// error returned by Println.

	// Output:
	// Kim is 22 years old.
}
ExamplePrintln()

Kim is 22 years old.

• 函数原型

Sprintln(a ...interface{}) string

• 官方注释
  Sprintln formats using the default formats for its operands and returns the resulting string.Spaces are always added between operands and a newline is appended.

• Arguement
  返回一个字符串，不做任何输出

func ExampleSprintln() {
	const name, age = "Kim", 22
	s := fmt.Sprintln(name, "is", age, "years old.")

	io.WriteString(os.Stdout, s) // Ignoring error for simplicity.

	// Output:
	// Kim is 22 years old.
}
ExampleSprintln()

Kim is 22 years old.

所有的函数名都是_print_格式的，其中_代表某个标志，标志及其含义如下：

且，
fmt.Fprintf和fmt.Printf是一对
fmt.Fprint和fmt.Print是一对
fmt.Fprintln和fmt.Println是一对
不带F前缀的函数均是对带F前缀函数的调用，其输入对象均设置为标准输出