# 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.
	
		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`.
	
		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.
	
		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.
	
		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.
	
		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.
	
		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.
	
		fmt.Printf("[%q]", strings.Trim(" !!! Achtung !!! ", "! "))
		Output:["Achtung"]

- func Fields(s string) []string

	Remove space items and split string with space into a slice.
	
		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.

		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.

		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.
		
		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, err := strconv.Itoa("1023")
			if err != nil {
				fmt.Println(err)
			}
			fmt.Println(a, b, c, d, e)
		}

## Links

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