int gzseek (int zp, int offset)
Sets the file position indicator for the file referenced by zp to offset bytes into the file stream. Equivalent to calling (in C) gzseek( zp, offset, SEEK_SET ).
If the file is opened for reading, this function is emulated but can be extremely slow. If the file is opened for writing, only forward seeks are supported; gzseek then compresses a sequence of zeroes up to the new starting position.
Upon success, returns 0; otherwise, returns -1. Note that seeking past EOF is not considered an error.
See also gztell() and gzrewind().