Golang placeholders %v, %+v, %#v give detailed explanations

package main

import "fmt"

type Person struct {
  Name string
  Age  int
}

func main() {
  person := Person{
    Name: "test",
    Age:  15,
  }
  ("%v\n", person)
  ("%+v\n", person)
  ("%#v\n", person)
}

The execution output is as follows:

{test 15}</code><code>{Name:test Age:15}</code><code>{Name:"test", Age:15}

1 Placeholder %v, %+v, %#v description

Placeholder Description
%v Output all value information
%+v The field name will be printed when printing the structure
%#v Go syntax representation of the corresponding value

2 Other placeholder descriptions

2.1 Boole

Placeholder       illustrate                Give an example                     Output
%t          true or false。Printf("%t", true)       true

2.2 Integer

Placeholder     illustrate                                  Give an example                       Output
%b      Binary representation                             Printf("%b", 5)             101
%c      correspondingUnicodeCharacters represented by code points              Printf("%c", 0x4E2D)        middle
%d      Decimal representation                             Printf("%d", 0x12)          18
%o      Octal representation                             Printf("%d", 10)            12
%q      Character literal value surrounded by single quotes，Depend onGoSyntax escapes safely  Printf("%q", 0x4E2D)        'middle'
%x      Hexadecimal representation，Letter form is lowercase a-f          Printf("%x", 13)             d
%X      Hexadecimal representation，Letter form in capital A-F          Printf("%x", 13)             D
%U      UnicodeFormat：U+1234，Equivalent to "U+%04X"    Printf("%U", 0x4E2D)         U+4E2D

2.3 String and byte slices

Placeholder          illustrate                              Give an example                           Output
%s      Output字符串表示（stringType or[]byte)    Printf("%s", []byte("Go"))  Golanguage
%q      String surrounded by double quotes，Depend onGoSyntax escapes safely   Printf("%q", "Go")         "Go"
%x      hexadecimal，Lowercase letters，Two characters per byte       Printf("%x", "golang")       676f6c616e67
%X      hexadecimal，uppercase letter，Two characters per byte       Printf("%X", "golang")       676F6C616E67

2.4 Pointer

Placeholder         illustrate                      Give an example                             Output
%p      Hexadecimal representation，Prefix 0x          Printf("%p", &amp;people)             0x4f57f0

2.5 Floating point numbers and complex numbers

Placeholder     illustrate                              Give an example            Output
%b      No decimal parts，Scientific notation method of power of exponential two，
        and  of 'b' Consistent conversion format。For example -123456p-78
%e      Scientific Counting Method，For example -1234.456e+78        Printf("%e", 10.2)     1.020000e+01
%E      Scientific Counting Method，For example -1234.456E+78        Printf("%e", 10.2)     1.020000E+01
%f      Have a decimal point but no exponent，For example 123.456        Printf("%f", 10.2)     10.200000
%g      Choose according to the situation %e or %f 以产生更紧凑of（无末尾of0）Output Printf("%g", 10.20)   10.2
%G      Choose according to the situation %E or %f 以产生更紧凑of（无末尾of0）Output Printf("%G", 10.20+2i)

Attachment: The difference between %v and %+v when printing the Go language structure

In Go,%vand%+vAll are placeholders for formatting the printing structure. Their differences are as follows:

%v: The default format is used to print the structure, only all field values of the structure are output, and the fields are separated by spaces.
%+v: Format the printing structure, the structure type and field name will be output, and the fields are separated by spaces.

For example, suppose there is a structurePersonThe definition is as follows:

type Person struct {
  Name string
  Age int
}

If aPersonType variablep, and use()When the function prints it, the output result is as follows:

p := Person{Name: "John Doe", Age: 30}

(p) // {John Doe 30}

use%vThe placeholder prints the structure and only outputs all field values of the structure, i.e.John Doeand30。

If used%+vPlaceholder prints the structure, and the structure type and field name will be output, i.e.Person{Name: John Doe, Age: 30}。

Summarize:

%v: The default format is the printing structure and only the field values are output.
%+v: Format the printing structure, output the structure type and field name.

Select the appropriate placeholder as needed to print the structure.

Summarize

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