//16进制 ---- > NSData ---- > unsigned char
uint32 i = CFSwapInt32(0x1569CD77);
NSLog(@"%d",i);
NSMutableData * mulData = [[NSMutableData alloc] init];
[mulData appendBytes:&i length:4];
NSLog(@"%@",mulData);
unsigned char * str = (unsigned char*)mulData.bytes;
NSLog(@"%s",str);
//int --- > NSData
int a = 11;
NSMutableData * mulData1 = [[NSMutableData alloc] init];
[mulData1 appendBytes:&a length:1];
NSLog(@"%@",mulData1);