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

下面来逐个分析

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

fmt.Fprintf

  • 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: %v\n", 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.

fmt.Printf

  • 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

optionaldescription
%d十进制整数
%x, %o, %b十六进制，八进制，二进制整数
%f, %g, %e浮点数，3.141593 3.141592653589793 3.141593e+00
%t布尔 ture或false
%c字符（rune）（Uniode码点）
%s字符串
%q带双引号的字符串"abc"或带单引号的字符’c'
%v变量的自然形式
%T变量的类型
%%字面上的百分号标志（无操作数）
fmt.Printf("整数：%d\t浮点数：%v\t字符串：%s\n", 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.

fmt.Sprintf

  • 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.

fmt.Fprint

  • 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: %v\n", 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.

fmt.Print

  • 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.

fmt.Sprint

  • 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.

fmt.Fprintln

  • 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: %v\n", err)
	}
	fmt.Println(n, "bytes written.")

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

Kim is 22 years old.
21 bytes written.

fmt.Println

  • 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.

fmt.Sprintln

  • 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.

总结

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：

标志含义
_f格式化
_ln换行
F_输入到某个对象
S_只返回而不做输出

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