Synchronously reads data up to the specified number of bytes.
- iOS 2.0+
- macOS 10.0+
- tvOS 9.0+
- watchOS 2.0+
The number of bytes to read from the receiver.
The data available through the receiver up to a maximum of
length bytes, or the maximum size that can be represented by an
NSData object, whichever is the smaller.
If the receiver is a file, this method returns the data obtained by reading
length bytes starting at the current file pointer. If
length bytes are not available, this method returns the data from the current file pointer to the end of the file. If the receiver is a communications channel, the method reads up to
length bytes from the channel. Returns an empty
NSData object if the file is positioned at the end of the file or if an end-of-file indicator is returned on a communications channel. This method raises
NSFile if attempts to determine the file-handle type fail or if attempts to read from the file or channel fail.