The gzwrite() function shall write data to the compressed file referenced by file, which shall have been opened in a write mode (see gzopen() and gzdopen()). On entry, buf shall point to a buffer containing len bytes of uncompressed data. The gzwrite() function shall compress this data and write it to file. The gzwrite() function shall return the number of uncompressed bytes actually written.
On success, gzwrite() shall return the number of
uncompressed bytes actually written to file.
On error gzwrite() shall return a value
less than or equal to
Applications may examine the cause using gzerror().
On error, gzwrite() shall set the error number associated with the stream identified by file to indicate the error. Applications should use gzerror() to access this error value.
An underlying base library function has indicated an error.
The global variable
The stream is invalid, is not open for writing, or is in an invalid state.
no compression progress is possible (see deflate()).
Insufficient memory available to compress.