I want to find the default handling application in my C program. Is there a C API with same functionality as xdg-mime query default mime-type on Linux?
Is there a glibc API that can find the default handing application for a MIME type on linux?
c;freedesktop;mime types
glibc doesn't know anything about MIME types; the API functions live at the level of desktop environment APIs, and the freedesktop.org recognize that harmonizing them is an impossible task so they only specify the shell-level interface.  You either use that via popen() or code for a particular desktop environment.