Structure 'zbx_dc_maintenance_tag_t' element name 'operator' is a reserved word in C++.

It breaks compilation with C++:

In file included from dbconfig.c:37:
dbconfig.h:657:24: error: expected type-specifier before ‘;’ token
  unsigned char operator;
                        ^

It could be fixed by renaming 'operator' (in 5 files) to some other name (.e.g. 'op').