将Unsigned Int转换为十六进制值

Question

How can I convert a integer 6 digit number such as "1234674" to a hexadecimal 4 byte NSData in Objective-C ?

This is the part of our code that sends passkey:

#define HSL_PRIVATE_SERVICE_UUID 0xFF20 
#define HSL_PRIVATE_NEW_PASSKEY_UUID 0xFF35 
unsigned int newPassKey = [_confirmNewPassKey.text intValue];
NSLog(@"newPasskey %d", newPassKey);
NSData *d = [NSData dataWithBytes:&newPassKey length:sizeof(unsigned int)];
[_t writeValue:HSL_PRIVATE_SERVICE_UUID characteristicUUID:HSL_PRIVATE_NEW_PASSKEY_UUID p:_peripheral data:d];

I did an air capture comparing BTOOL versus iPhone passkey writes.

BTOOL (A simulator tool) wrote (the correct result) :

0x40e201 

iPhone wrote(wrong data):

 0x0001e240 

Not sure what is going on and how to fix it in the app so that the result matches what the Bluetooth device is expecting . I would like the result to be same as BTOOL one.

Answer 1

Try this:

uint32_t value = [_confirmNewPassKey.text intValue];
uint32_t swapped = CFSwapInt32HostToBig(value);
NSData *d = [NSData dataWithBytes:&swapped length:sizeof(swapped)];

This assumes you want big endian for the output.