Deep in the formatted output in Golang

fmt

The commonly used standard library for Go language to control text output is fmt

The main functions used for output in fmt are:

• Print: Output to the console, no formatting operations are accepted
• Println: Output to the console and wrap the line
• Printf: Format output, you can only print out formatted strings, and you can only output variables of string type directly (you cannot directly output other types)
• Sprintf: Format and return a string without any output
• Fprintf: to format and output to instead

format

Use the Printf function to test the string formatting in Go language:

(Format style, parameter list…)

Format style: string form, formatting symbols start with %, %s string format, %d decimal integer format

Parameter list: Multiple parameters are separated by commas, and the number must correspond to the number in the format style one by one, otherwise an error will be reported during runtime.

for example:

username := "boy"
("welcome, %s", username)

Integer formatting

func main() {
    ("%b \n", 123) //1111011
    ("%o \n", 123) //173
    ("%d \n", 123) //123
    ("%x \n", 123) //7b
    ("%X \n", 123) //7B   
    ("%c \n", 123) //{
    ("%U \n", 123) //U+007B 
}

Floating point number formatting

func main() {
    ("%e \n", 123.456) //1.234560e+02
    ("%E \n", 123.456) //1.234560E+02
    ("%f \n", 123.456) //123.456000
    ("%F \n", 123.456) //123.456000
    ("%g \n", 123.456) //123.456
    ("%G \n", 123.456) //123.456 
}

Boolean type formatting

func main() {
    ("%t", true) //true
}

Character formatting

func main() {
    ("%c", 0x4E2D) //middle}

String formatting

func main() {
    ("%s \n", "Hello world") //Hello world
    ("%q \n", "Hello world") //"Hello world"
    ("%x \n", "Hello world") //48656c6c6f20776f726c64
    ("%X \n", "Hello world") //48656C6C6F20776F726C64
}

Pointer Format

func main() {
    a := "Hello world"
    b := &a
    ("%p \n", b)  //0xc000046230
    ("%#p \n", b) //c000046230
}

Universal placeholder

func main() {
    ("%v \n", "Hello World")   //Hello World
    ("%+v \n", "Hello World")  //Hello World
    ("%#v \n", "Hello World")  //"Hello World"
    ("%T \n", "Hello World")   //string
    ("%%%v \n", "Hello World") //%Hello World
}

Width representation

Floating point precision control

The width is specified by a decimal number immediately following the percent sign. If the width is not specified, the value is not filled except necessary.

The accuracy is specified by a decimal number followed by a (optional) width followed by a dot number. If no precision is specified, the default precision will be used; if the dot is not followed by a number, the precision is 0. For example,

func main() {
    ("|%f|\n", 123.456)     //|123.456000|
    ("|%12f|\n", 123.456)   //|  123.456000|
    ("|%.3f|\n", 123.456)   //|123.456|
    ("|%12.3f|\n", 123.456) //|     123.456|
    ("|%|\n", 123.456)  //|         123|
}

String length control

Width setting format: add a number in the middle of the placeholder, the number is divided into positive and negative, +: right aligned, -: left aligned

Minimum width: the percentage sign is followed by the decimal number. If the part is not enough, you can choose to add 0.

Maximum width: Decimal number after the decimal point, the excess part will be truncated

func main() {
    ("|%s|\n", "123.456")    //|123.456|
    ("|%12s|\n", "123.456")  //|     123.456|
    ("|%-12s|\n", "123.456") //|123.456     |
    ("|%012s|\n", "123.456") //|00000123.456|
    ("|%.5s|\n", "123.456")  //|123.4|
}

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