iphone - Convert hex data string to NSData in Objective C (cocoa)

Question

fairly new iPhone developer here. Building an app to send RS232 commands to a device expecting them over a TCP/IP socket connection. I've got the comms part down, and can send ASCII commands fine. It's the hex code commands I'm having trouble with.

So lets say I have the following hex data to send (in this format):

x1Cx02dx00x00x00xFFx7F

How do I convert this into an NSData object, which my send method expects?

Obviously this does not work for this hex data (but does for standard ascii commands):

NSString *commandascii;
NSData *commandToSend;
commandascii = @"x1Cx02dx00x00x00xFFx7F";
commandToSend = [commandascii dataUsingEncoding:NSStringEncoding];

For a start, some of the x hex codes are escape characters, and I get an "input conversion stopped..." warning when compiling in XCode. And NSStringEncoding obviously isn't right for this hex string either.

So the first problem is how to store this hex string I guess, then how to convert to NSData.

Any ideas?

Answer 1

Code for hex in NSStrings like "00 05 22 1C EA 01 00 FF". 'command' is the hex NSString.

command = [command stringByReplacingOccurrencesOfString:@" " withString:@""];
NSMutableData *commandToSend= [[NSMutableData alloc] init];
unsigned char whole_byte;
char byte_chars[3] = {'','',''};
for (int i = 0; i < ([command length] / 2); i++) {
    byte_chars[0] = [command characterAtIndex:i*2];
    byte_chars[1] = [command characterAtIndex:i*2+1];
    whole_byte = strtol(byte_chars, NULL, 16);
    [commandToSend appendBytes:&whole_byte length:1]; 
}
NSLog(@"%@", commandToSend);