Libclang does not detect function calls defined in headers

Question

I am using libclang to parse .cpp and get all function calls in the file. However , the only returned function calls are the one defined at the parsed .h / .cpp file not all the ones from the include files.

for example I am parsing example.cpp which include

#include "a.h" 
#include "example.h"

All calls for functions defined/declared in example.h are detected but it skips all function calls which are defined in a.h. How can I detect both of them ?

In a.h

foo ();

In example.hpp

boo();

In example.cpp

foo();
boo();

Only boo() is detected as function call. It does not check for function call recursivly in all headers. How can I force this check ?

I am using this function to return function calls

CXChildVisitResult functionVisitor(CXCursor cursor){              
    CXCursorKind cursorKind     = clang_getCursorKind(cursor);
    CXString     cursorSpelling = clang_getCursorSpelling(cursor);

    if (cursorKind == CXCursor_CallExpr) {
        CXString cursorUsr = clang_getCursorUSR(cursor);
        print_function_prototype(cursor);
        clang_disposeString(cursorUsr);
    }

    return CXChildVisit_Continue;
}