Go String Fundamentals

Introduction

In the previous lesson, we learned that characters in Go are encoded using UTF-8 and stored as either the byte or rune types. Now, let's discuss strings, which are collections of characters. Let's explore this topic together.

Knowledge Points:

• What is a string
• Creating a string
• Declaring a string
• Common string functions

Skills Graph

What is a String

In the first program we learned in Go, we printed the string "hello, world".

A string is a basic data type in Go, also known as a string literal. It can be understood as a collection of characters and occupies a continuous block of memory. This block of memory can store any type of data, such as letters, text, emoji, and so on.

However, unlike other languages, strings in Go are immutable and cannot be modified.

Creating a String

Strings can be declared in several ways. Let's take a look at the first method. Create a new file called string.go:

touch ~/project/string.go

Write the following code:

package main

import "fmt"

func main() {
    // Use the var keyword to create a string variable a
    var a string = "labex"
    a = "labex" // Assign "labex" to variable a

    // Declare variable b and assign its value
    var b string = "labs"

    // Type declaration can be omitted
    var c = "Monday"

    // Use := for quick declaration and assignment
    d := "Sunday"
    fmt.Println(a, b, c, d)
}

The above code demonstrates how to create strings using the var keyword and the := operator. If you assign a value when creating a variable with var, you can omit the type declaration, as shown in the creation of variable c.

go run string.go

The expected output is as follows:

labex labs Monday Sunday

Declaring a String

In most cases, we use double quotes "" to declare strings. The advantage of double quotes is that they can be used as escape sequences. For example, in the program below, we use the \n escape sequence to create a new line:

package main

import "fmt"

func main() {
    x := "linux\nlabex"
    fmt.Println(x)
}

go run string.go

The expected output is as follows:

linux
labex

Here are some common escape sequences:

If you want to preserve the original format of the text or need to use multiple lines, you can use backticks to represent them:

package main

import "fmt"

func main() {
    // Output the ASCII art of "labex"
    ascii := `
        ##        ###   ######  ####### ##    ##         ##       ##  ##  ##    ## ##       ##  ##         ##      ##    ## ######  ######    ###         ##      ####### ##    ## ##        ###         ##      ##    ## ##    ## ##       ##  ##         ####### ##    ## ######  ####### ##    #`
    fmt.Println(ascii)
}

Backticks are commonly used in prompts, HTML templates, and other cases where you need to preserve the original format of the output.

Getting the Length of a String

In the previous lesson, we learned that English characters and general punctuation marks occupy one byte, while Chinese characters occupy three to four bytes.

Therefore, in Go, we can use the len() function to get the byte length of a string. If there are no characters that occupy multiple bytes, the len() function can be used to accurately measure the length of the string.

If a string contains characters that occupy multiple bytes, you can use the utf8.RuneCountInString function to get the actual number of characters in the string.

Let's see an example. Write the following code to the string.go file:

package main

import (
    "fmt"
    "unicode/utf8"
)

func main() {
    // Declare two empty strings using var and :=
    var a string
    b := ""

    c := "labex"

    // Output byte length
    fmt.Printf("The value of a is %s, the byte length of a is: %d\n", a, len(a))
    fmt.Printf("The value of b is %s, the byte length of b is: %d\n", b, len(b))
    fmt.Printf("The value of c is %s, the byte length of c is: %d\n", c, len(c))

    // Output string length
    fmt.Printf("The length of c is: %d\n", utf8.RuneCountInString(c))
}

go run string.go

The expected output is as follows:

The value of a is , the byte length of a is: 0
The value of b is , the byte length of b is: 0
The value of c is labex, the byte length of c is: 5
The length of c is: 5

In the program, we first declared two empty strings and the string labex. You can see that their byte lengths and actual lengths are the same.

Converting Strings and Integers

We can use functions from the strconv package to convert between strings and integers:

package main

import (
    "fmt"
    "strconv"
)

func main() {
    // Declare a string a and an integer b
    a, b := "233", 223

    // Use Atoi to convert a string to an integer
    c, _ := strconv.Atoi(a)

    // Use Sprintf and Itoa functions respectively
    // to convert an integer to a string
    d1 := fmt.Sprintf("%d", b)
    d2 := strconv.Itoa(b)

    fmt.Printf("The type of a: %T\n", a)   // string
    fmt.Printf("The type of b: %T\n", b)   // int
    fmt.Printf("The type of c: %T\n", c)   // int
    fmt.Printf("The type of d1: %T\n", d1) // string
    fmt.Printf("The type of d2: %T\n", d2) // string
}

go run string.go

The expected output is as follows:

The type of a: string
The type of b: int
The type of c: int
The type of d1: string
The type of d2: string

In the program, we use the Sprintf() function from the fmt package, which has the following format:

func Sprintf(format string, a ...interface{}) string

format is a string with escape sequences, a is a constant or variable that provides values for the escape sequences, and ... means that there can be multiple variables of the same type as a. The string after the function represents that Sprintf returns a string. Here's an example of using this function:

a = fmt.Sprintf("%d+%d=%d", 1, 2, 3)
fmt.Println(a) // 1+2=3

In this code snippet, the format is passed with three integer variables 1, 2, and 3. The %d integer escape character in format is replaced by the integer values, and the Sprintf function returns the result after replacement, 1+2=3.

Also, note that when using strconv.Atoi() to convert a string to an integer, the function returns two values, the converted integer val and the error code err. Because in Go, if you declare a variable, you must use it, we can use an underscore _ to ignore the err variable.

When strconv.Atoi() converts correctly, err returns nil. When an error occurs during conversion, err returns the error message, and the value of val will be 0. You can change the value of string a and replace the underscore with a normal variable to try it yourself.

Concatenating Strings

The simplest way to concatenate two or more strings is to use the + operator. We can also use the fmt.Sprintf() function to concatenate strings. Let's take a look at an example:

package main

import (
    "fmt"
)

func main() {
    a, b := "lab", "ex"
    // Concatenate using the simplest method, +
    c1 := a + b
    // Concatenate using the Sprintf function
    c2 := fmt.Sprintf("%s%s", a, b)
    fmt.Println(a, b, c1, c2) // lab ex labex labex
}

go run string.go

The expected output is as follows:

lab ex labex labex

In the program, we also used the Sprintf() function from the fmt package to concatenate strings and print the results.

Removing Leading and Trailing Spaces from a String

We can use the strings.TrimSpace function to remove leading and trailing spaces from a string. The function takes a string as input and returns the string with leading and trailing spaces removed. The format is as follows:

func TrimSpace(s string) string

Here is an example:

package main

import (
    "fmt"
    "strings"
)

func main() {
    a := " \t \n  labex \n \t labs"
    fmt.Println(strings.TrimSpace(a))
}

go run string.go

The expected output is as follows:

labex
         labs

Summary

To summarize what we have learned in this lesson:

• The relationship between strings and characters
• Two ways to declare strings
• Concatenating strings
• Removing leading and trailing whitespace from a string

In this lesson, we have explained the strings we use in daily life. We have learned about the relationship between strings and characters, mastered string creation and declaration, and gained some knowledge of common string functions.