Go offers excellent support for string formatting in the printf tradition. Here are examples of common string formatting tasks.
Structs
type point struct {
x, y int
}
p := point{1, 2}
fmt.Printf("struct1: %v\n", p)
// Output: struct1: {1 2}
fmt.Printf("struct2: %+v\n", p)
// Output: struct2: {x:1 y:2}
fmt.Printf("struct3: %#v\n", p)
// Output: struct3: main.point{x:1, y:2}
Prints the value in a default format
For structs, includes field names
Prints a Go syntax representation of the value
Types and Booleans
fmt.Printf("type: %T\n", p)
// Output: type: main.point
fmt.Printf("bool: %t\n", true)
// Output: bool: true
fmt.Printf("int: %d\n", 123)
// Output: int: 123
fmt.Printf("float1: %f\n", 78.9)
// Output: float1: 78.900000
fmt.Printf("float2: %e\n", 123400000.0)
// Output: float2: 1.234000e+08
fmt.Printf("float3: %E\n", 123400000.0)
// Output: float3: 1.234000E+08
fmt.Printf("str1: %s\n", "\"string\"")
// Output: str1: "string"
fmt.Printf("str2: %q\n", "\"string\"")
// Output: str2: "\"string\""
fmt.Printf("str3: %x\n", "hex this")
// Output: str3: 6865782074686973
fmt.Printf("pointer: %p\n", &p)
// Output: pointer: 0xc0000140a0
Width and Precision
Integer Width
fmt.Printf("width1: |%6d|%6d|\n", 12, 345)
// Output: width1: | 12| 345|
Float Width and Precision
fmt.Printf("width2: |%6.2f|%6.2f|\n", 1.2, 3.45)
// Output: width2: | 1.20| 3.45|
fmt.Printf("width3: |%-6.2f|%-6.2f|\n", 1.2, 3.45)
// Output: width3: |1.20 |3.45 |
String Width
fmt.Printf("width4: |%6s|%6s|\n", "foo", "b")
// Output: width4: | foo| b|
fmt.Printf("width5: |%-6s|%-6s|\n", "foo", "b")
// Output: width5: |foo |b |
Printf
func(format string, a ...any) (n int, err error)
Prints formatted string to os.Stdout
Sprintf
func(format string, a ...any) string
Formats and returns a string without printing
Fprintf
func(w io.Writer, format string, a ...any) (n int, err error)
Formats and prints to an io.Writer
s := fmt.Sprintf("sprintf: a %s", "string")
fmt.Println(s)
// Output: sprintf: a string
fmt.Fprintf(os.Stderr, "io: an %s\n", "error")
// Writes to stderr
Package Reference