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The Way to Go

Strings and strconv Package

In this lesson, you'll study strings, strconv package, and the functions supported by them.

We'll cover the following...

Strings are a basic data structure, and every language has a number of predefined functions for manipulating strings. In Go, these are gathered in a package, strings. We’ll discuss below some very useful functions one by one.

Prefixes and suffixes

HasPrefix tests whether the string s begins with a prefix prefix:

strings.HasPrefix(s, prefix string) bool

HasSuffix tests whether the string s ends with a suffix suffix:

strings.HasSuffix(s, suffix string) bool

The following program implements these functions:

Go (1.6.2)
package main
import (
    "fmt"
    "strings"
)
func main() {
    var str string = "This is an example of a string"
    fmt.Printf("T/F? \nDoes the string \"%s\" have prefix %s? ", str, "Th")
    fmt.Printf("\n%t\n\n", strings.HasPrefix(str, "Th"))    // Finding prefix
    fmt.Printf("Does the string \"%s\" have suffix %s? ", str, "ting")
    fmt.Printf("\n%t\n\n", strings.HasSuffix(str, "ting"))  // Finding suffix
}

As you can see in the above code, we declare a string str and initialize it with This is an example of a string at line 9. At line 11, we used the function HasPrefix to find prefix Th in string str. The function returns true because str does start with Th. Similarly, at line 14, we used the function HasSuffix to find the suffix ting in string str. The function returns false because str does not end with ting. This also illustrates the use of the escape character \ to output a literal " with \" , and the use of 2 substitutions in a format-string.

Testing whether a string contains a substring

The function Contains returns true if substr is within s:

strings.Contains(s, substr string) bool

Indicating the index a substring or character in a string

Index returns the index of the first instance of str in s, or -1 if str is not present in s:

strings.Index(s, str string) int

LastIndex returns the index of the last instance of str in s, or -1 if str is not present in s:

strings.LastIndex(s, str string) int

If ch is a non-ASCII character, use:

strings.IndexRune(s string, ch int) int.

The following program finds the index of the substrings in a string:

Go (1.6.2)
package main
import (
    "fmt"
    "strings"
)
func main() {
    var str string = "Hi, I'm Marc, Hi."
    fmt.Printf("The position of the first instance of\"Marc\" is: ")
    fmt.Printf("%d\n", strings.Index(str, "Marc"))      // Finding first occurence
    fmt.Printf("The position of the first instance of \"Hi\" is: ")
    fmt.Printf("%d\n", strings.Index(str, "Hi"))        // Finding first occurence
    fmt.Printf("The position of the last instance of \"Hi\" is: ")
    fmt.Printf("%d\n", strings.LastIndex(str, "Hi"))    // Finding last occurence
    fmt.Printf("The position of the first instance of\"Burger\" is: ")
    fmt.Printf("%d\n", strings.Index(str, "Burger"))    // Finding first occurence
}

As you can see in the above code, we declare a string str and initialize it with Hi, I’m Marc, Hi. at line 8. At line 10, we find the index of the first occurrence of Marc ...