The gzprintf() function shall format data as for fprintf(), and write the resulting string to the compressed file stream file.
The gzprintf() function
shall return the number of uncompressed bytes
actually written, or a value less than or equal to
0 in the event of an error.
If file is
NULL, or refers to a
compressed file stream that has not been opened for writing,
gzprintf() shall return Z_STREAM_ERROR.
Otherwise, errors are as for gzwrite().