You cannot define a function using a typedef for a function type. It’s explicitly forbidden – refer to 6.9.1/2 and the associated footnote:
The identifier declared in a function definition (which is the name of the function) shall
have a function type, as specified by the declarator portion of the function definition.The intent is that the type category in a function definition cannot be inherited from a typedef:
typedef int F(void); // type F is "function with no parameters // returning int" F f, g; // f and g both have type compatible with F F f { /* ... */ } // WRONG: syntax/constraint error F g() { /* ... */ } // WRONG: declares that g returns a function int f(void) { /* ... */ } // RIGHT: f has type compatible with F int g() { /* ... */ } // RIGHT: g has type compatible with F F *e(void) { /* ... */ } // e returns a pointer to a function F *((e))(void) { /* ... */ } // same: parentheses irrelevant int (*fp)(void); // fp points to a function that has type F F *Fp; //Fp points to a function that has type F