File Operations

Brendan Hansen

use core.os
use core.io
use core.string
use core {
    printf
}

#doc "Writes example text into a file."
write_data_into_file :: (filename: str) {
    // This is one way of opening a file: call os.open and then os.close later.
    // os.open returns a Result(os.File, os.FileError), so it must be handled
    // to use the os.File. This program opts to unwrap the result.
    file := os.open(filename, .Write)->unwrap()
    defer os.close(&file)

    // Create an io.Writer over the file stream using io.writer_make.
    // Also, free it later by defering io.writer_free. This also flushes
    // the internal buffer of io.Writer to make sure everything is written
    // to the file.
    file_writer := io.Writer.make(&file)
    defer io.Writer.free(&file_writer)

    // The simplest way of writing a string to the file.
    file_writer->write("This is the first line of text.\n")

    // io.write_format can be used to "printf" into a file.
    // printf can be thought of as io.write_format(&stdio.stream, ...).
    file_writer->write_format("This is a {} line of text.\n", "formatted")

    for i in 0 .. 5 {
        file_writer->write_format("Another line numbered {}.\n", i)
    }
}

#doc "Reads example text from a file."
read_whole_file :: (filename: str) {
    // This is the simplest way to get the entire content of a file
    // into a string ([] u8). Also, defer "deleting" the string, which
    // will free the memory allocated for the string.
    contents := os.get_contents(filename)
    defer delete(&contents)

    printf("Whole contents:\n{}\n", contents)
}

main :: () {
    filename := "test.txt"

    write_data_into_file(filename)
    read_whole_file(filename)
}