Using memset to clear base class members

Question

I see code like below and don’t like it. Especially memset(static_cast(this), 0, sizeof(BaseStruct)); I need arguments for refactoring and found one here: Why can it be dangerous to use this POD struct as a base class?

Do you see more problems? Is vtable in danger?

// abstract class
class BaseA {
public:
    virtual void doSomethingA() = 0;
};

// no method, no virtual method, only simple data
typedef struct BaseStruct {
    int x;
    float y;
    long z[10];
} BaseStruct;

class Subclass : public BaseA, public BaseStruct {
public:
    virtual void doSomethingA() {}
    virtual void doSomethingElse() {}
    void resetBaseA() {
        memset(static_cast<BaseStruct*>(this), 0, sizeof(BaseStruct));
    }
};

It's undefined behaviour. Nothing more needs to be said to justify binning the whole thing. — Kerrek SB, Apr 09 '14 at 12:02
possible duplicate of [Empty derived optimization](http://stackoverflow.com/questions/21838292/empty-derived-optimization) — Kerrek SB, Apr 09 '14 at 12:03
Replace the `memset` with `*this = BaseStruct();` or, in C++11, `static_cast(*this) = {};`. Zeroing without the nasty undefined behavior. — Casey, Apr 09 '14 at 12:36
Here are some solutions: http://stackoverflow.com/a/38103250/3223828 — Stuart Gillibrand, Jun 29 '16 at 18:15

score 0 · Accepted Answer · answered Apr 09 '14 at 12:07

0

BaseStruct has no virtual member, so you should be good. vtbl should be for BaseA. However, better would be if could reset each individual member explicitly. That's recommended.

answered Apr 09 '14 at 12:07

Dr. Debasish Jana

6,980
4
30
69

Using memset to clear base class members

1 Answers1