Where to start to use CRC for error checking?

I am trying to use CRC for error checking for downloaded files. I used NSURLConnection for downloading file. But I have no idea where to start to use CRC for error checking. Do I use some libraries? If so, would you recommend me one?开发者_JAVA百科 Can anyone tell me where I can find any examples or tutorials for CRC usage in c++ or objective c? Thank you very much

First off, how is the file CRC handled on the server (if at all)? There are a multitude of algorithms (CRC32 for simple checksum, MD5/SHA for cryptographic hashes) which can be used, and you must use the same one. If the server does not provide any checksum information (say, from a checksum file), there is no use for a checksum as there is nothing to compare it to.