Reading of compressed files happens in a transparent manner - there is nothing the developer has to do to support this.
Writing of compressed files is controlled through the SoOutput::setCompression method.
The list of available compression methods can be fetched with the SoOutput::getAvailableCompressionMethods method.
You can not use file compression together with I/O to memory buffers, except for reading from memory buffers containing gzip-compressed files.
For backwards compatibility with Coin 2.0 and Coin 1.0, compressed files must not be used. Compressed files works only from Coin 2.1 and upwards.