Error in replacing the bytes.

Question

Hi all,
I like to implement "System.arraycopy" method of java in objective C. I have implemented as follows :
+(BOOL)copyBuffer:(NSData *)srcdata_ :(int)srcIndex :(unsigned char*)dest :(int)destIndex :(int)destLength
BOOL isCopied = YES;
@try
NSMutableData *subData = (NSMutableData *)[srcdata_ subdataWithRange:NSMakeRange(srcIndex, destLength)];
NSMutableData *destData = (NSMutableData *)[NSData dataWithBytes:dest length:20];
[destData replaceBytesInRange:NSMakeRange(destIndex, destLength) withBytes:[subData bytes] ];//length:destLength];
dest = (unsigned char*)[destData bytes];
@catch (NSException *exp)
NSLog(@"Error in copying the array : %@", [exp reason]);
isCopied = NO;
return isCopied;
- But the above code returns following exception.
"* -[NSConcreteData replaceBytesInRange:withBytes:]: unrecognized selector sent to instance 0xd21b90" .. I have checked the range , but the range lies in the length of the source.
I tried but couldnt spot the error.
Any help would be greatly appreciated.
Regards,
Mohammed Sadiq.

Answer 1

Mohammed Sadiq wrote:
NSMutableData *destData = (NSMutableData *)[NSData dataWithBytes:dest length:20];
The above typecast simply turns off the compiler warning. It doesn't change the type of the object. So destData is not a mutable object and the attempt to modify it causes the exception.
Try something like this:
NSMutableData *destData = [NSMutableData dataWithBytes:dest length:20];
[destData replaceBytesInRange:NSMakeRange(destIndex, destLength) withBytes:subData];
Note that your subData object is also not mutable for the same reason, though in the posted code this shouldn't matter.
- Ray