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 s

Answer 1

If I want to hard-code the bytes, I do something like this:

enum { numCommandBytes = 8 };
static const unsigned char commandBytes[numCommandBytes] = { 0x1c, 0x02, 'd', 0x0, 0x0, 0x0, 0xff, 0x7f };

If you're obtaining these backslash-escaped bytes at run time, try the strunvis function.

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

NSString *commandascii;
NSData *commandToSend;
commandascii = @"\x1C\x02d\x00\x00\x00\xFF\x7F";
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.

First, it's Xcode, with a lowercase c.

Second, NSStringEncoding is a type, not an encoding identifier. That code shouldn't compile at all.

More to the point, backslash-escaping is not an encoding; in fact, it's largely independent of encoding. The backslash and 'x' are characters, not bytes, which means that they must be encoded to (and decoded from) bytes, which is the job of an encoding.