File read (load), write (save)

There are many ways to read and write files of various formats. Class File reads/writes simple text or raw binary data.

string file = @"C:\Test\test.txt";

Read all text to a string.

string text = File.ReadAllText(file);
print.it(text);

Read if file exists.

string text2 = File.Exists(file) ? File.ReadAllText(file) : null;

Write all text from a string.

File.WriteAllText(file, text); //creates new file or overwrites existing file

Read text lines.

string[] lines = File.ReadAllLines(file);
foreach (var s in lines) {
	print.it(s);
}

Write text lines from List.

var a = new List<string>();
for (int i = 1; i <= 10; i++) a.Add("line " + i);
File.WriteAllLines(file, a);

Usually text in files is Unicode, encoded as UTF-8 or UTF-16. The ReadX functions can read both. The WriteX functions write UTF-8 by default. Let's write UTF-16:

File.WriteAllText(file, text, Encoding.Unicode);

If the file already exists, the WriteX functions overwrite (replace) it, else they create new file. The AppendX functions append to existing file or create new file.

File.AppendAllText(file, "line\r\n"); //append a string

File.AppendAllLines(file, a); //append a list or array

Read/write binary (non-text) data.

byte[] b = File.ReadAllBytes(file);
File.WriteAllBytes(file, b);

All above functions immediately fail if the file is locked at that time (eg an app is writing the file). Also the write functions can corrupt the file in some cases. To read and write in a safer way, use filesystem functions.

text = filesystem.loadText(file); //waits max 2 s if locked
text = filesystem.waitIfLocked(() => File.ReadAllText(file), 10_000); //waits max 10 s if locked

See also filesystem.saveText and similar functions. They write in a safer way and can create a backup file.