Input Stream Scanner

A simple scanner for any kind of file input streams with arbitrary delimiters. Made with Swift, based on NSScanner.

Originally appeared as a necessity to parse the standard input for competitive programming challenges on HackerRank.

Installation

For competitive programming

Copy-paste the contents of this tiny sample and enjoy. For more general use cases check out the full version of StreamScanner.swift and see the usage and examples sections below.

As a framework

Compile, link against and don't forget to:

import StreamScanner

As a built-in class

Add StreamScanner.swift file to your project.

Usage

For convenience you can declare:

let stdin = StreamScanner.standardInput

and use stdin later on. Spaces and new lines are considered delimiters by default.

Or make your custom stream with:

let stream = StreamScanner(source: FileHandle(forReadingAtPath: "/path/to/file"),
                           delimiters: CharacterSet(charactersIn: "-.:\n"))

Now call read() -> Optional<T> to get the next value from a stream, where T is a type of a variable where you want to read() the stream.

You may call ready() -> Bool to check whether the stream currently contains any data it can parse. Note: the stream may try to grab some data from its source during this check.

Example

Imagine there's a file at /path/to/file with the following contents:

42.times show:not_a_double

And here's one of the ways to scan it with the stream just declared above:

var number: Int?    = stream.read() //parse an integer at the current position in the stream
var string: String? = stream.read() //now skip a delimiting dot and parse a string
var double: Double? = stream.read() //now skip a delimiting colon and try to parse a double

print("\(number) \(string) \(double)")  //Optional(42) Optional("times show") nil

More Examples

Read some arbitrary values of different types from the standard input

if
    let int:    Int     = stdin.read(),
    let string: String  = stdin.read(),
    let double: Double  = stdin.read(),
    let int64:  Int64   = stdin.read(),
    let float:  Float   = stdin.read()
{
    print("\(int) \(string) \(double) \(int64) \(float)")
}

Input:

+42 st_ring!
-0.987654321 12345678900
.42

Output:

42 st_ring! -0.987654321 12345678900 0.42

Read an array of Int64 of an arbitrary size from the standard input

if var count: Int = stdin.read()
{
    var array: [Int64] = []

    for _ in 0..<count
    {
        if let integer: Int64 = stdin.read()
        {
            array.append(integer)
        }
    }

    print(array)
}

Input:

2
1234567890123456789 987654321098765432

Output:

[1234567890123456789, 987654321098765432]

Read some strings from the stream in a for loop until it's empty

for name in stdin
{
    print("Hello, \(name)!")
}

Input:

Chris Ally Joshua

Output:

Hello, Chris!
Hello, Ally!
Hello, Joshua!

Read and present the contents of /etc/passwd file

if let input = FileHandle(forReadingAtPath: "/etc/passwd")
{
    let scanner = StreamScanner(source: input, delimiters: CharacterSet(charactersIn: ":\n"))

    print("User Database:")

    while let line: String = scanner.read()
    {
        //skip any comments
        if !line.hasPrefix("#")
        {
            let username = line

            if
                let valid:    String  = scanner.read(),
                let userId:   Int     = scanner.read(),
                let groupId:  Int     = scanner.read(),
                let gecos:    String  = scanner.read(),
                let home:     String  = scanner.read(),
                let shell:    String  = scanner.read()
            {
                print("------------------------------")
                print("User: \t\(username) (\(gecos))")
                print("UID:  \t\(userId)")
                print("GID:  \t\(groupId)")
                print("Home: \t\(home)")
                print("Shell:\t\(shell)")
            }
        }
    }
}

Output:

User Database:
------------------------------
User: 	nobody (Unprivileged User)
UID:  	-2
GID:  	-2
Home: 	/var/empty
Shell:	/usr/bin/false
------------------------------
User: 	root (System Administrator)
UID:  	0
GID:  	0
Home: 	/var/root
Shell:	/bin/sh
------------------------------
User: 	daemon (System Services)
UID:  	1
GID:  	1
Home: 	/var/root
Shell:	/usr/bin/false

License

This toy is free and open.