build-web-application-with-golang/en/07.6.md

# 7.6 Strings

On the web, almost everything we see (including user inputs, database access, etc.), is represented by strings. They are a very important part of web development. In many cases, we also need to split, join, convert and otherwise manipulate strings. In this section, we are going to introduce the `strings` and `strconv` packages from the Go standard library.

## strings

The following functions are from the `strings` package. See the official documentation for more details:

- func Contains(s, substr string) bool

	Check if string `s` contains string `substr`, returns a boolean value.
```Go	
fmt.Println(strings.Contains("seafood", "foo"))
fmt.Println(strings.Contains("seafood", "bar"))
fmt.Println(strings.Contains("seafood", ""))
fmt.Println(strings.Contains("", ""))

//Output:
//true
//false
//true
//true
```
- func Join(a []string, sep string) string

	Combine strings from slice with separator `sep`.
```Go	
s := []string{"foo", "bar", "baz"}
fmt.Println(strings.Join(s, ", "))
//Output:foo, bar, baz		
```			
- func Index(s, sep string) int 

	Find index of `sep` in string `s`, returns -1 if it's not found.
```Go	
fmt.Println(strings.Index("chicken", "ken"))
fmt.Println(strings.Index("chicken", "dmr"))
//Output:4
//-1
```
- func Repeat(s string, count int) string

	Repeat string `s` `count` times.
```Go	
fmt.Println("ba" + strings.Repeat("na", 2))
//Output:banana
```
- func Replace(s, old, new string, n int) string

	Replace string `old` with string `new` in string `s`. `n` is the number of replacements. If n is less than 0, replace all instances.
```Go	
fmt.Println(strings.Replace("oink oink oink", "k", "ky", 2))
fmt.Println(strings.Replace("oink oink oink", "oink", "moo", -1))
//Output:oinky oinky oink
//moo moo moo
```
- func Split(s, sep string) []string

	Split string `s` with separator `sep` into a slice.
```Go	
fmt.Printf("%q\n", strings.Split("a,b,c", ","))
fmt.Printf("%q\n", strings.Split("a man a plan a canal panama", "a "))
fmt.Printf("%q\n", strings.Split(" xyz ", ""))
fmt.Printf("%q\n", strings.Split("", "Bernardo O'Higgins"))
//Output:["a" "b" "c"]
//["" "man " "plan " "canal panama"]
//[" " "x" "y" "z" " "]
//[""]
```
- func Trim(s string, cutset string) string

	Remove `cutset` of string `s` if it's leftmost or rightmost.
```Go	
fmt.Printf("[%q]", strings.Trim(" !!! Achtung !!! ", "! "))
Output:["Achtung"]
```
- func Fields(s string) []string

	Remove space items and split string with space into a slice.
```Go	
fmt.Printf("Fields are: %q", strings.Fields("  foo bar  baz   "))
//Output:Fields are: ["foo" "bar" "baz"]
```

## strconv

The following functions are from the `strconv` package. As usual, please see official documentation for more details:

- Append series, convert data to string, and append to current byte slice.
```Go
package main

import (
	"fmt"
	"strconv"
)

func main() {
	str := make([]byte, 0, 100)
	str = strconv.AppendInt(str, 4567, 10)
	str = strconv.AppendBool(str, false)
	str = strconv.AppendQuote(str, "abcdefg")
	str = strconv.AppendQuoteRune(str, '单')
	fmt.Println(string(str))
}
```
- Format series, convert other data types into string.
```Go
package main

import (
	"fmt"
	"strconv"
)

func main() {
	a := strconv.FormatBool(false)
	b := strconv.FormatFloat(123.23, 'g', 12, 64)
	c := strconv.FormatInt(1234, 10)
	d := strconv.FormatUint(12345, 10)
	e := strconv.Itoa(1023)
	fmt.Println(a, b, c, d, e)
}
```
- Parse series, convert strings to other types.
```Go		
package main

import (
	"fmt"
	"strconv"
)

func main() {
	a, err := strconv.ParseBool("false")
	if err != nil {
		fmt.Println(err)
	}
	b, err := strconv.ParseFloat("123.23", 64)
	if err != nil {
		fmt.Println(err)
	}
	c, err := strconv.ParseInt("1234", 10, 64)
	if err != nil {
		fmt.Println(err)
	}
	d, err := strconv.ParseUint("12345", 10, 64)
	if err != nil {
		fmt.Println(err)
	}
	e := strconv.Itoa(1023)
	fmt.Println(a, b, c, d, e)
}
```
## Links

- [Directory](preface.md)
- Previous section: [Files](07.5.md)
- Next section: [Summary](07.7.md)