You've probably been reading C++ material. Only in C++ int f(); and int f(void); are identical. In C, however, int f(); Declares a function taking

You've probably been reading C++ material. Only in C++ int f(); and int f(void); are identical. In C, however, int f(); Declares a function taking any number of arguments. In C++, that would be denoted as int f(...); Which is unfortunately a syntax error in traditional C as the ellipsis is only allowed following some explicit parameters. (It's not that big a deal; you'd have to #ifdef __cplusplus extern "C" #endif in the header of the C library for C++ compatibility anyway (to prevent function name mangling and thus link errors), so you can #ifdef the () and (...) too.) FWIW, C++ does support the legacy int f(void); syntax, but its use is discouraged except for headers which are also to be used for C code.