Understanding of pure c struct and c ++ struct, and understanding of c struct

Understanding of pure c struct and c ++ struct, and understanding of c struct

// Main. cpp

// If the file name is. the end of cpp indicates that this is a c ++ source program. // in the c ++ source program, the role of class is exactly the same as that of struct, // except for their default member attributes (the class is private by default, // struct is common by default), and struct has this pointer, and struct // can inherit, struct also supports all the attributes of c ++ polymorphism. Also, struct // has a virtual table. Below is an example of a struct virtual table. // Remember that in the source file at the End of. cpp, struct is basically the same as the class. # Include <stdlib. h> # include <stdio. h> struct A {virtual void fun () = 0 ;}; struct B: public A {void fun () {printf ("B: fun () \ n ") ;}}; typedef void (* PF) (); void Printf (void * arg) {PF f = PF (* (int *) arg ); f () ;}void test () {B B; Printf (int *) * (int *) & B) ;}int main () {test (); return 0 ;}

// Main. c

# Include <stdlib. h> # include <stdio. h> // because the struct attributes in pure c language are different from those in c ++. // First, struct in pure C language does not support polymorphism and cannot be constructed. // without this, there cannot be a function, if we use a pure c struct to simulate a class, it will be very difficult. below is my rough writing. Struct A; typedef void (* PF) (struct A * this); // array of function pointers. Struct vPtrNode; typedef void (* PV) (struct vPtrNode * this); struct vPtrNode {PV pf; // simulate a virtual table .}; Void vtrprintf (struct vPtrNode * this) {printf ("vtrprintf () \ n");} struct A {PF f; // because the struct in pure C language cannot define functions, function pointers are used instead. Int a; struct vPtrNode * vptr; struct B {PF p; struct A * B; // simulate inheritance so that struct B calls A function in Base Class.} B ;}; void fun1 (struct A * this) // simulate the this pointer. {This-> a = 100; printf ("fun1 (): a = % d \ n", this-> a);} int main () {struct A; a. f = (PF) fun1; // simulate this. A. f (& a); //. b. p = (PF) fun1; // The pattern subclass function p overwrites function f in the base class. A. b. p (& a);. b. B = (struct A *) malloc (sizeof (struct A); // space must be opened here. If no space is opened, A block error occurs when you assign a definite // function address to the pointer. A. B. B-> f = (PF) fun1; a. B. B-> f (& a); // simulate a subclass to call the function f of the parent class. /// // The virtual table only exists in the parent class. A. vptr = (struct vPtrNode *) malloc (sizeof (struct vPtrNode);. vptr-> pf = (PV) vtrprintf; struct vPtrNode vptr;. vptr-> pf (& vptr); return 0 ;}

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