How do I check if a string is a substring of another string in Go?
For example, I want to check someString.contains("something").
2 Answers
Use the function Contains from the strings package.
import (
"strings"
)
strings.Contains("something", "some") // true
To compare, there are more options:
import (
"fmt"
"regexp"
"strings"
)
const (
str = "something"
substr = "some"
)
// 1. Contains
res := strings.Contains(str, substr)
fmt.Println(res) // true
// 2. Index: check the index of the first instance of substr in str, or -1 if substr is not present
i := strings.Index(str, substr)
fmt.Println(i) // 0
// 3. Split by substr and check len of the slice, or length is 1 if substr is not present
ss := strings.Split(str, substr)
fmt.Println(len(ss)) // 2
// 4. Check number of non-overlapping instances of substr in str
c := strings.Count(str, substr)
fmt.Println(c) // 1
// 5. RegExp
matched, _ := regexp.MatchString(substr, str)
fmt.Println(matched) // true
// 6. Compiled RegExp
re = regexp.MustCompile(substr)
res = re.MatchString(str)
fmt.Println(res) // true
Benchmarks:
Contains internally calls Index, so the speed is almost the same (btw Go 1.11.5 showed a bit bigger difference than on Go 1.14.3).
BenchmarkStringsContains-4 100000000 10.5 ns/op 0 B/op 0 allocs/op
BenchmarkStringsIndex-4 117090943 10.1 ns/op 0 B/op 0 allocs/op
BenchmarkStringsSplit-4 6958126 152 ns/op 32 B/op 1 allocs/op
BenchmarkStringsCount-4 42397729 29.1 ns/op 0 B/op 0 allocs/op
BenchmarkStringsRegExp-4 461696 2467 ns/op 1326 B/op 16 allocs/op
BenchmarkStringsRegExpCompiled-4 7109509 168 ns/op 0 B/op 0 allocs/op
