HowToWriteDataToAFile

I realize that there are many ways to do this. If you could take a look at how I did it and see why it is making my program crash, I would appreciate it!

    //Declare variables
    NSSavePanel *sp;
NSData	*textBuffer= [[NSData new] getBytes:@"Hello, World!"];

   //Open the save panel
sp = [[NSSavePanel alloc] init];
[sp runModal];

if([sp filename])		// Makes sure the user chose a file and directory
{

            //Write the string in textBuffer into a file with the filename chosen by the user
            [textBuffer writeToFile:[sp filename] atomically:true];  //<-This is where it is crashing
}	

//Release the save panel object
[sp release];
    [textBuffer release];

The way you create your NSData is probably the problem. Try:

NSData	*textBuffer= [[NSData alloc] initWithBytes:"Hello, World!" length:13];

or better (but don’t release)

NSData	*textBuffer= [@"Hello, World!" dataUsingEncoding:NSUTF8StringEncoding allowLossyConversion:YES];

–CharlesParnot

Thank you Charles! This also seems to work…

NSString *myString = @”Hello, World!”; const char *utfString = [myString UTF8String]; NSData *textBuffer= [NSData dataWithBytes:utfString length:strlen(utfString)];

there were several problems with the original code. use of +new wasn’t one of them; despite being obscure and rarely-used, it is not deprecated according to any Apple documentation I know of (feel free to correct me on this).

http://developer.apple.com/documentation/Cocoa/Reference/Foundation/ObjC_classic/Classes/NSObject.html#//apple_ref/doc/uid/20000050/new

*- You are hereby corrected *

getBytes: does not return an NSData instance (not the one passed in, nor any other), it returns void. using the return value of a void function or method is Very Very Bad.
getBytes: takes a data buffer for output; you passed in a constant string as input. writing random data over a Cocoa instance is also Very Very Bad. (you have already found one solution for this: +dataWithBytes::. CharlesParnot’s -[NSString dataUsingEncoding::] solution is better, though.)

–boredzo

Thanks for the details! I would just add about new: as used here, it will return a new instance of NSData, which is immutable, and empty (I think). Can’t do much from there. –CharlesParnot (note to the OP: many mistakes in just 3 lines of code, that seem to miss some of the basics of Cocoa/ObjC - maybe you should get a little bit of experience in things other than NSData first, even if you are very familiar with C ;-)

Just don’t forget to check that OK was pressed in addition to a proper filename. If the user enters a filename and hits Cancel, the code above will still write your file. So edit the following two lines from above to:

int return_flag = [sp runModal];

if([sp filename] && return_flag == NSFileHandlingPanelOKButton)		// Makes sure the user chose a file and directory AND hit OK

Seal68

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