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Re: file programming in the Gnustep framework

From: Richard Frith-Macdonald
Subject: Re: file programming in the Gnustep framework
Date: Tue, 1 Jan 2008 17:39:47 +0000

Hash: SHA1

On 1 Jan 2008, at 15:13, Arno R. Schleich wrote:


I am just starting to use the framework. I am looking for some tutorial
like stuff on file I/O in GNUStep. Is it advisable not to use "lower
level" constructs such as fprintf etc at all ? From reading the online
documentation for file handle/ file manager I could not figure out how
to perform a trivial task like reading a variable length file of real
numbers. Any hints where I would find some beginner's
examples/instructions regarding file I/O ?

You should probably use NSFileManager to manage files (listing, moving, deleting etc).

For low level I/O you would use NSFileHandle or NSStream.
For instance, to read the variable length file you could do the job in two lines ...

NSFileHandle *handle = [NSFileHandle fileHandleForReadingAtpath: @"myfile"];
NSData                  *contents = [handle readDataToEndOfFile];

That being said, you might do it in one line with:

NSData  *contents = [NSData dataWithContentsOfFile: @"myfile"];

If you want to read the file a bit at a time ...

NSInputStream *istream = [NSInputStream inputStreamWithFileAtPath: @"myfile"];
double                  number;

while ([istream read: (uint8_t*)&number maxLength: sizeof(number)] == sizeof(number))
     // do something with each number here.

For portability, you would want the numbers to be stored in a standard byte ordering, so you would use NSSwapBigDoubleToHost() to convert from network byte ordering to host byte ordering.

Of course, you might not want to do this sort of low-level stuff, but rather work with objects serialised to file.

I suggest looking at property-list objects (NSString, NSNumber, NSArray, NSDictionary, NSData, NSDate) as combinations of these objects can be written to or read from file as a single operation (eg. write an array of numbers by using the -writeToFile:atomically: method and read it back using [NSArray arrayWithContentsOfFile: @"afile"]) as these are great for a huge variety of applications.

To deal with complex groupings of arbitrary objects I'd recommend using NSKeyedArchiver or NSKeyedUnarchiver

For the equivalent of printf/scanf you would normally be appending to a mutable string (using appendFormat:) or scanning a string (using the NSScanner class) and using the -writeToFile:atomically: and stringWithContentsOfFile: methods to perform the file I/O (or converting the string to an NSData object and using NSFileHandle or NSStream if you want to send it over a network connection).

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