LNK2019 error message while linking QT with static lib

output.log

2>xxxwidget.obj : error LNK2019: unresolved external symbol "void __cdecl yyy::zzzstring(...)" (?zzzstring@xxx@@YAXPAU_GUID@@AAV?$basic_string@GU?$char_traits@G@std@@V?$allocator@G@2@@std@@@Z) referenced in function __catch$?nnn@mmm@@...... :

fatal error LNK1120: 1 unresolved externals