iphone - Converting floats to NSData and back in Objective-C

Question

In an iphone application, I'm looking to convert a float to NSData for it to be sent over bluetooth and then converted back again when it's received. I have the bluetooth part working fine, but when I use this to convert to NSData:

NSData *data = [[NSData alloc]init];

float z = 9.8574; // Get the float value, 9.8574 is just an example

[data getBytes:&z length:sizeof(float)];

I can not convert it back to a float. I've tried a couple of methods but I'm wondering if this is the correct way to encode the float to NSData??

Thanks

Answer 1

Here is how to encode and decode a float with NSData:

encoding:

NSMutableData * data = [NSMutableData dataWithCapacity:0];
float z = ...;
[data appendBytes:&z length:sizeof(float)];

decoding:

NSData * data = ...; // loaded from bluetooth
float z;
[data getBytes:&z length:sizeof(float)];

A couple of things to note here:

1. You have to use NSMutableData if you are going to add things to the data object after creating it. The other option is to simply load the data all in one shot:

NSData * data = [NSData dataWithBytes:&z length:sizeof(float)];

2. the getBytes:length: method is for retrieving bytes from an NSData object, not for copying bytes into it.