Yes and no. Yes, that is a valid #define; but the following program must work: #include <stdio.h> #undef getc int main(void) { getc(stdin);

Yes and no. Yes, that is a valid #define; but the following program must work: #include <stdio.h> #undef getc int main(void) { getc(stdin); return 0; } so it cannot be implemented as only a macro.