Question

I want to save float values stored in an array into a text file and read the file directly on Mac. This is how I create the array:

dataArray = [[NSMutableArray alloc] init];
NSNumber *numObj = [NSNumber numberWithFloat:3.14];
[dataArray insertObject:numObj atIndex:0];
NSNumber *numObj = [NSNumber numberWithFloat:2.3];
[dataArray insertObject:numObj atIndex:1];
...

This is how I save the array:

NSData *savedData = [NSKeyedArchiver archivedDataWithRootObject:dataArray];
NSString *filePath = @"/Users/smith/Desktop/dataArray.txt";
[savedData writeToFile:filePath options:NSDataWritingAtomic error:nil];

When I open the file, the contents are just garbled letters. Instead, I want to make it something like this:

3.14
2.3
1.4
...

Answer 1

You can use componentsJoinedByString: to make an in-memory representation first, and then write that representation into a file, like this:

NSString *fileRep = [dataArray componentsJoinedByString:@"\n"];
NSString *filePath = @"/Users/smith/Desktop/dataArray.txt";
[fileRep writeToFile:filePath options:NSDataWritingAtomic error:nil];

This assumes that the number of items is relatively small, because the string representation is created entirely in memory.

Reading back is not as nice as writing out, though: you start by reading back a string, theb split it to components using [fileRep componentsSeparatedByString:@"\n"], and then go through components in a loop or with a block, adding [NSNumber numberWithDouble:[element doubleValue]] for each element of your split.