YouTipGo Fmt Sprintf
[ Go Basic Syntax](#)
Go can use fmt.Sprintf to format strings, as follows:
fmt.Sprintf(Formatting Verb, Parameter List...)
* **Formatting Verb:** In string form, formatting specifiers start with %, %s for string format, %d for decimal integer format.
* **Parameter List:** Multiple parameters separated by commas, the number must match the number in the formatting verb, otherwise a runtime error will occur.
## Example
package main
import(
"fmt"
"io"
"os"
)
func main(){
// go: format string and assign to new string, use fmt.Sprintf
// %s represents string
var stockcode="000987"
var enddate="2020-12-31"
var url="Code=%s&endDate=%s"
var target_url=fmt.Sprintf(url,stockcode,enddate)
fmt.Println(target_url)
// Another example, %d represents integer
const name, age ="Kim",22
s := fmt.Sprintf("%s is %d years old.n", name, age)
io.WriteString(os.Stdout, s)// For simplicity, ignore some errors
}
The output is:
Code=000987&endDate=2020-12-31Kim is 22 years old.
## Example
package main
import(
"fmt"
"io"
"os"
)
func main(){
// Declare numeric variables
const num1, num2, num3 =5,10,15
// Call Sprintf() function
s := fmt.Sprintf("%d + %d = %d", num1, num2, num3)
// Use WriteString() function to output the result to terminal
// "os.Stdout" is the content of the string
io.WriteString(os.Stdout, s)
}
The output is:
5 + 10 = 15
Go String Formatting Verbs:
| Format | Description |
| --- | --- |
| %v | Output the original value |
| %+v | On the basis of %v, expand the struct field names and values |
| %#v | Output the value in Go syntax format |
| %T | Output the type and value in Go syntax format |
| %% | Output % itself |
| %b | Integer displayed in binary |
| %o | Integer displayed in octal |
| %d | Integer displayed in decimal |
| %x | Integer displayed in hexadecimal |
| %X | Integer displayed in hexadecimal with uppercase letters |
| %U | Unicode character |
| %f | Floating point number |
| %p | Pointer, displayed in hexadecimal |
## Example
package main
import"fmt"
func main(){
name :="John"
age :=30
height :=175.5
result := fmt.Sprintf("Name: %s, Age: %d, Height: %.2f", name, age, height)
fmt.Println(result)
}
In the above example, in the format string "Name: %s, Age: %d, Height: %.2f", %s, %d and %.2f are replaced by the values of name, age and height variables respectively, where %.2f represents floating point format with two decimal places.
The output is:
Name: John, Age: 30, Height: 175.50
%.2f is a floating point formatting option, it is used to control the decimal precision of floating point numbers, where **2** represents the number of decimal places to keep, you can modify it as needed.
More usage examples:
## Example
package main
import(
"fmt"
"os"
)
type point struct{
x, y int
}
func main(){
p := point{1,2}
fmt.Printf("%vn", p)
fmt.Printf("%+vn", p)
fmt.Printf("%#vn", p)
fmt.Printf("%Tn", p)
fmt.Printf("%tn",true)
fmt.Printf("%dn",123)
fmt.Printf("%bn",14)
fmt.Printf("%cn",33)
fmt.Printf("%xn",456)
fmt.Printf("%fn",78.9)
fmt.Printf("%en",123400000.0)
fmt.Printf("%En",123400000.0)
fmt.Printf("%sn",""string"")
fmt.Printf("%qn",""string"")
fmt.Printf("%xn","hex this")
fmt.Printf("%pn",&p)
fmt.Printf("|%6d|%6d|n",12,345)
fmt.Printf("|%6.2f|%6.2f|n",1.2,3.45)
fmt.Printf("|%-6.2f|%-6.2f|n",1.2,3.45)
fmt.Printf("|%6s|%6s|n","foo","b")
fmt.Printf("|%-6s|%-6s|n","foo","b")
s := fmt.Sprintf("a %s","string")
fmt.Println(s)
fmt.Fprintf(os.Stderr,"an %sn","error")
}
The output is:
{1 2}{x:1 y:2} main.point{x:1, y:2} main.point true1231110!1c878.9000001.234000e+081.234000E+08"string"""string""68657820746869730xc0000b4010| 12| 345|| 1.20| 3.45||1.20 |3.45 || foo| b||foo |b | a string an error
### Alignment
By using width and alignment parameters in the format string, you can control the alignment of the generated string.
Common alignment parameters are:
* `%s`: String format, can use the following alignment parameters:
* `%s`: Default alignment, left-aligned.
* `%10s`: Right-aligned with width 10.
* `%-10s`: Left-aligned with width 10.
* `%d`: Integer format, can use the following alignment parameters:
* `%d`: Default alignment, right-aligned.
* `%10d`: Right-aligned with width 10.
* `%-10d`: Left-aligned with width 10.
* `%f`: Floating point format, can use the following alignment parameters:
* `%f`: Default alignment, right-aligned.
* `%10f`: Right-aligned with width