View Compilation Error

0_0_29767740_1410.cpp: In function 'int main()':
0_0_29767740_1410.cpp:30:42: error: invalid conversion from 'int (*)(const c*, const c*)' to 'int (*)(const void*, const void*)' [-fpermissive]
         qsort(d, n, sizeof(struct c), cmp);
                                          ^
In file included from 0_0_29767740_1410.cpp:2:0:
GCC4.9.2/x86_64-w64-mingw32/include/stdlib.h:353:16: note: initializing argument 4 of 'void qsort(void*, size_t, size_t, int (*)(const void*, const void*))'
   void __cdecl qsort(void *_Base,size_t _NumOfElements,size_t _SizeOfElements,int (__cdecl *_PtFuncCompare)(const void *,const void *));
                ^