Reads From Stdin the Input Entered by Alice

At my electric current job we have some projects that were realized using the Go programming language. The cool thing is, programmers that have used it are in beloved with it, and these applications never crash, not even under heavy load. This is great, for example, for applications that have to process a stream of data as fast as possible.

Then, I decided to become through HackerRank and do the 30 days challenge. I exercise not wait to become a Truthful Adept© only, at least, I'd like to catch up with the syntax and all the rest.

(Probably, in the long run, we're going to sunset these Go projects because nosotros got caused by another company, and their main programming language is Coffee, sooooo….)

I will not go through installing the go compiler, Go figure out past yourself. But this hello world may give you lot (and me) a sense of what's going on here.

On the educative task of explaining Hello World

When I was at university my Java teacher asked students to write the all-time-possible explanation of Java'due south Hullo World, that would win a Java book (Java 1.iv, I'm that former). And then I wrote a 4 pages essay explaining everything (keywords, exceptions…) and yep, I own that volume now :)

This "do" is really valid and I encourage everyone to exercise it. Yous volition do a lot of research to explicate tiny details that ordinarily do not seem to have much importance. So, for example, it took me 4-v hours to write this article. The issue is that I feel confident of what I learned.

Things you should know earlier nosotros write some code

Go is a compiled programming language. This means that to run your program yous first need to compile it using the become executable.

Go source files have the .go extension. And then, to compile a file:

          $ go build hi-earth.become  $ ls  hello-world how-do-you-do-world.go                  

Go compiler volition create a hello-globe executable that we tin dejeuner, on Linux and Mac systems, by running ./hello-world .

Some may say that it's boring to compile & launch and so Go offers the run way, that will execute the two steps for yous:

          $ get run hello-world.go  .... (plan output here)                  

And finally: get has an official formatting tool. This means that you cannot decide how many spaces (or tabs), or how long your lines should be, etc. Smart IDEs like Visual Studio Code with the Go extension will automagically run the formatting tool for yous at every save. Only if yous want to run it from the command line:

          $ get fmt hello-world.go                  

No more bug on git merge :)

Permit'due south become back to the source code

The exercise track:

save a line of input from stdin to a variable, impress Hi, World. on a single line, and finally print the value of your variable on a 2d line.

Hither'due south the source code:

          package master  import ( 	"bufio" 	"fmt" 	"os" )  func main() { 	var reader = bufio.NewReader(bone.Stdin) 	message, _ := reader.ReadString('\n')  	fmt.Println("How-do-you-do, World.") 	fmt.Println(message) }                  

Let's break up and analyse the code in parts.

the parcel declaration

          parcel master                  

All become lawmaking must declare its package. Executable files must be in a main parcel, and the start office that is executed on the offset run is the main part.

Import block

          import ( 	"bufio" 	"fmt" 	"os" )                  

Here, we are importing iii packages from the go standard library:

• fmt is the formatted I/O library and contains functions to read and write from I/O similar printf and scanf in C.
• bufio is the package that will perform buffered i/o operations. basically, we desire to read a bunch of characters at a fourth dimension, and this is the package that contains the easiest functions.
• os provides a platform-contained interface to operating system functionality.

I must be honest with you, in my first endeavor to write this block, I wrote:

          import "fmt" import "bufio" import "bone"                  

This is legal syntax, but the go formatter decided that wrapping all packages inside a singleimport proclamation is better. If the formatter goes with the other syntax, it'southward probably better to use it from the start.

role declarations

          func main() {   ... }                  

Another slice of syntax from get: to declare functions we write func followed by the function name. If the file must exist executable, the function must be called primary() and be in the main packet.

You may enquire, "what is the syntax if I want to pass arguments? and return values?" Ok, here's a slightly more complex example:

          func addMult(a,b int)(int, int) {    return a+b, a*b }                  

wtf? well, this means that this function accepts two parameters in input (a and b) and will render ii values, that you lot can assign. Nosotros'll come across an instance in the next block.

Read input from STDIN

          var reader = bufio.NewReader(bone.Stdin) message, _ := reader.ReadString('\n')                  

Here we are declaring reader variable with var and bulletin variable without var. Why?

To only declare a variable, without initializing, you can use the keyword var followed past the variable name; yous must also declare a blazon.

If the blazon tin can be inferred by the assigning expression, it can be omitted.

If the variable is initialized and assigned in the same moment, Go offers the shorthand syntax via := that allows to avoid the var keyword. So the offset line may be written every bit:

          reader := bufio.NewReader(os.Stdin)                  

As I specified before, the bufio library contains functions that allow to read in a buffer. The buffer we are creating is reading from STDIN, that is a mutual name for the Standard Input. Basically, what the user types in the last.

Once we get a reference to the reader, we apply it to read a string using the method ReadString(). ReadString accepts a character (that is wrapped in single quotes, '' instead of strings that use double quotes, "") that will be used to match the cease of the buffer line. But… what's on the left side of the assignment?

          bulletin, _ := ...                  

We merely hit our first multi-return function. ReadString returns ii values, the data read and the fault; we should take care of the error variable (in Go, if you lot declare a variable and you will not apply it, the program will non compile at all), but if we want to skip the variable assignment, we tin simply set up to _ (underscore) and Go compiler will stop protesting. So, in a scenario like reading from a file or from the network, where obviously something may go incorrect, skipping the error cheque is not a good idea. In this case, given the simplicity of the program, we take our responsibilities as grown adults.

Writing to STDOUT

Outputting data is much simpler:

          fmt.Println("Hello, Earth.") fmt.Println(bulletin)                  

In this snippet, nosotros are writing "Hello World" followed by the message nosotros captured at the previous step. That'southward it. Program concluded.

Where is the power of Go?

You may not see it from this very uncomplicated programme, but:

• being compiled, and strongly typed, many errors will exist caught at compile time.
• multi-render values allow for the error-checking pattern that is verbose, but produces some very robust code.
• Become shines on multithreaded applications using "channels", more on that in the next manufactures. Equally I said, my colleagues wrote a super-fast information processor that never breaks, fifty-fifty nether heavy load.

Below I get out some links that I checked while writing this article. Explore them similar I did. Good day!

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More resources:

• how to install go for your Bone (golang.org)
• many other ways to read input in Go (from zetcode.com)
• difference of quotes in Go (from golangbyexample.com)
• anatomy of functions in go (past runGo)
• Go by example: variables
• ReadString specification (golang.org)

Tags: go • hello world

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Source: https://michelenasti.com/2020/09/16/how-to-read-and-write-from-stdin-and-stdout-in-go.html

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