TypeCasting结构和类

Question

I am very new to C++. Currently I am reviewing a source code where I saw some typecasting, but I didn't understand it.
Here is the code.

struct str {
    char *a;
    int b;
};

class F {
public:
    char* val;
};  

F f1;  

Can anyone explain the below Assignement Please.or is that typecasting valid??

 str* ptr = (str*) f1->val;  

Answer 1

Can anyone explain the below Assignement Please.

It means "pretend that the val pointer points to an object of type str , even though it's declared to point to a completely different type char ; give me that pointer and trust that I know what I'm doing".

That's assuming that the real code either declares F * f1; , or accesses it as f1.val ; the code you've posted won't compile.

or is that typecasting valid??

If the pointer really does point to an object of the correct type, then it's valid; otherwise, using the pointer will cause the program to fail in all sorts of catastrophic ways.

Typecasting is something that should very rarely be necessary. If you really do need it, you should never (as in absolutely never, under any circumstances) use that C-style cast; it means "force the conversion with no checks whatsoever, as long as there's some way to do it, even if it makes absolutely no sense". Use static_cast or dynamic_cast when you can, and reinterpret_cast or const_cast when you're doing something really dodgy. And don't use any of them unless you know what you're doing, and have a very good reason for circumventing the type system.