Convert uint8_t to NSString - ios

Question

Just started learning objective-c and was trying to convert a byte array into UTF8 NSString but have been getting nil/null.
Here is the abbreviated code sample.
enum {
TMessageType_CALL = 1,
TMessageType_REPLY = 2,
TMessageType_EXCEPTION = 3,
TMessageType_ONEWAY = 4
};
int32_t VERSION_1 = 0x80010000;
int value = VERSION_1 | TMessageType_CALL;
uint8_t buff[4];
buff[0] = 0xFF & (value >> 24);
buff[1] = 0xFF & (value >> 16);
buff[2] = 0xFF & (value >> 8);
buff[3] = 0xFF & value;
//Convert buff to NSString with offset =0, length =4
I tried the following.
NSString *t = [[NSString alloc] initWithBytes:buff length:4 encoding:NSUTF8StringEncoding];
NSString *t1 = [NSString stringWithUTF8String:(char *)buff];
But both t and t1 return nil.
What is the right API to convert it correctly?
This conversion needs to be generic across WriteI32() writeI64(), writeString(), writeDouble(). Here is the code for the rest.
- (void) writeI16: (short) value
{
uint8_t buff[2];
buff[0] = 0xff & (value >> 8);
buff[1] = 0xff & value;
[mTransport write: buff offset: 0 length: 2];
}
- (void) writeI64: (int64_t) value
{
uint8_t buff[8];
buff[0] = 0xFF & (value >> 56);
buff[1] = 0xFF & (value >> 48);
buff[2] = 0xFF & (value >> 40);
buff[3] = 0xFF & (value >> 32);
buff[4] = 0xFF & (value >> 24);
buff[5] = 0xFF & (value >> 16);
buff[6] = 0xFF & (value >> 8);
buff[7] = 0xFF & value;
[mTransport write: buff offset: 0 length: 8];
}
- (void) writeDouble: (double) value
{
// spit out IEEE 754 bits - FIXME - will this get us in trouble on
// PowerPC?
[self writeI64: *((int64_t *) &value)];
}
- (void) writeString: (NSString *) value
{
if (value != nil) {
const char * utf8Bytes = [value UTF8String];
size_t length = strlen(utf8Bytes);
[self writeI32: length];
[mTransport write: (uint8_t *) utf8Bytes offset: 0 length: length];
} else {
// instead of crashing when we get null, let's write out a zero
// length string
[self writeI32: 0];
}
}

Answer 1

buff is an array of unsigned chars, so you could use this:
NSString *t = [NSString stringWithFormat:#"%s", buff];
As an alternative, you can get each character explicitly:
NSMutableString *t = [NSMutableString stringWithCapacity:4];
for (NSUInteger i = 0; i < 4; ++i)
[t appendFormat:#"%c", buff[i]];
NSLog(#"%#", t);
The first option does a conversion to a valid string. The second option gives you each character, regardless of any terminating characters ('\0').
I'm not sure what useful information this will give you, but there you have it.