Go fmt.Printf format strings

Go Language Basic Syntax

fmt.Printf is a powerful output formatting function in the Go language, mainly used to format strings and output the result to standard output (usually the console).

fmt.Printf formats subsequent variables according to the specified format string; the syntax is as follows:

fmt.Printf(格式化样式, 参数列表…)

• Formatting style:String form, formatting symbols begin with%Starts with %; %s is string format, %d is decimal integer format.
• Parameter list:Multiple parameters are separated by commas, and the number must correspond one-to-one with the number in the format string, otherwise an error will be reported at runtime.

Output result:

hello, John Doe
hello, JOHN DOE
John Doe is 27 years old
John Doe is %!f(int=27) years old

Go string formatting symbols:

The format string consists of regular text and format placeholders.

Formatting placeholder with% Starts with %, followed by one or more characters that specify the format type.

The structure of a formatting placeholder is:

%[flags][width][.precision]verb

• flagsFlags used to control formatted output (optional).
  • -: Left-aligned.
  • +: Always display the sign of the value.
  • 0: padded with zeros.
  • #Adds a prefix for binary, octal, hexadecimal, etc.
  • Space: Positive numbers preceded by a space, negative numbers preceded by-。
• width: Output width (optional).
• .precisionNumber of digits after the decimal point for floating-point numbers (optional).
• verb: Used to specify the formatting method of the data.

1. Formatting integers

fmt.Printf("十进制: %d, 二进制: %b, 八进制: %o, 十六进制: %x\n", 42, 42, 42, 42)
// 输出：十进制: 42, 二进制: 101010, 八进制: 52, 十六进制: 2a

2. Formatting floating-point numbers

fmt.Printf("普通: %f, 科学计数法: %e, 自动: %g\n", 123.456, 123.456, 123.456)
// 输出：普通: 123.456000, 科学计数法: 1.234560e+02, 自动: 123.456

3. Formatting strings

fmt.Printf("普通字符串: %s, 带引号: %q, 十六进制: %x\n", "Go", "Go", "Go")
// 输出：普通字符串: Go, 带引号: "Go", 十六进制: 476f

4. Using width and alignment

fmt.Printf("|%10s|%-10s|\n", "right", "left")
// 输出：|     right|left      |

5. Formatting structs

type User struct {
    Name string
    Age  int
}
user := User{Name: "Alice", Age: 30}
fmt.Printf("默认: %v\n带字段名: %+v\nGo语法: %#v\n", user, user, user)
// 输出：
// 默认: {Alice 30}
// 带字段名: {Name:Alice Age:30}
// Go语法: main.User{Name:"Alice", Age:30}

6. Formatting boolean values

fmt.Printf("布尔值: %t, %t\n", true, false)
// 输出：布尔值: true, false

Output result:

{1 2}
{x:1 y:2}
main.point{x:1, y:2}
main.point
true
123
1110
!
1c8
78.900000
1.234000e+08
1.234000E+08
"string"
"\"string\""
6865782074686973
0xc0000b4010
|    12|   345|
|  1.20|  3.45|
|1.20  |3.45  |
|   foo|     b|
|foo   |b     |
a string
an error

Go Language Basic Syntax