Finding wether or not a substring in a string

Table of Contents

To find a substring in a string its fairly simple, using Go official package, there is several functions, This functions outlines the functions

They all return a boolean, to determine wether the substring exists or not

func SubstringsPreAndSuffix() {
    phrase := "Don't communicate by sharing memory, share memory by communicating."
    searchFor := "communicate"
    contain := strings.Contains(phrase, searchFor)
    fmt.Printf("The string: \"%s\" The needle \"%s\", %t\n", phrase, searchFor, contain)
    searchFor = "channel"
    contain = strings.Contains(phrase, searchFor)
    fmt.Printf("The string: \"%s\" The needle \"%s\", %t\n", phrase, searchFor, contain)
    searchFor = "Don"
    contain = strings.HasPrefix(phrase, searchFor)
    fmt.Printf("HasPrefix The needle \"%s\", %t\n", searchFor, contain)
    searchFor = "communicating."
    contain = strings.HasSuffix(phrase, searchFor)
    fmt.Printf("HasSuffix The needle \"%s\", %t\n", searchFor, contain)
}

You can try it yourself

under the hood #

Contains function explained #

The Contains function simply checks whether the string has a given substring. Using the index function Contains function uses index function to determine wether or not the substring exits. When provided with a string, the contains pass it to the index function, so if substring is present it returns a greater than -1, the Contains function returns true. otherwise it s false

func Contains(s, substr string) bool {
    return Index(s, substr) >= 0
}

Has (Prefix/Suffix) function explained #

Contrary to the containts, the strings package uses a different implemenration for the HasSuffix and HasPrefix functions, have two actions:

It first checks the length of both strings (needle and haystack), then it performs a comparison, if the comparison is satisfieid, the substring is shorter or equal to the string,
It performs the required part to be checked for existstence or negation.

func HasSuffix(s, suffix string) bool {
    return len(s) >= len(suffix) && s[len(s)-len(suffix):] == suffix
}
func HasPrefix(s, prefix string) bool {
    return len(s) >= len(prefix) && s[0:len(prefix)] == prefix
}