Read and write an integer to/from a .txt file

How can I read and write an integer to and from a text file, and is it possible to r开发者_开发技巧ead or write to multiple lines, i.e., deal with multiple integers?

Thanks.

This is certainly possible; it simply depends on the exact format of the text file.
Reading the contents of a text file is easy:

// If you want to handle an error, don't pass NULL to the following code, but rather an NSError pointer.
NSString *contents = [NSString stringWithContentsOfFile:@"/path/to/file" encoding:NSUTF8StringEncoding error:NULL];

That creates an autoreleased string containing the entire file. If all the file contains is an integer, you can just write this:

NSInteger integer = [contents integerValue];

If the file is split up into multiple lines (with each line containing one integer), you'll have to split it up:

NSArray *lines = [contents componentsSeparatedByCharactersInSet:[NSCharacterSet newlineCharacterSet]];
for (NSString *line in lines) {
    NSInteger currentInteger = [line integerValue];
    // Do something with the integer.
}

Overall, it's very simple.

Writing back to a file is just as easy. Once you've manipulated what you wanted back into a string, you can just use this:

NSString *newContents = ...; // New string.
[newContents writeToFile:@"/path/to/file" atomically:YES encoding:NSUTF8StringEncoding error:NULL];

You can use that to write to a string. Of course, you can play with the settings. Setting atomically to YES causes it to write to a test file first, verify it, and then copy it over to replace the old file (this ensures that if some failure happens, you won't end up with a corrupt file). If you want, you can use a different encoding (though NSUTF8StringEncoding is highly recommended), and if you want to catch errors (which you should, essentially), you can pass in a reference to an NSError to the method. It would look something like this:

NSError *error = nil;
[newContents writeToFile:@"someFile.txt" atomically:YES encoding:NSUTF8StringEncoding error:&error];
if (error) {
    // Some error has occurred. Handle it.
}

For further reading, consult the NSString Class Reference.

If you have to write to multiple lines, use \r\n when building the newContents string to specify where line breaks are to be placed.

NSMutableString *newContents = [[NSMutableString alloc] init];

for (/* loop conditions here */)
{
    NSString *lineString = //...do stuff to put important info for this line...
    [newContents appendString:lineString];
    [newContents appendString:@"\r\n"];
}