How to check the virtual function table size?# Programming - 葵花宝典
z*e
1 楼
Is there any way to get vptr or check the size of virtual function table?
thx.
thx.
c*e
2 楼
Statically, I think you can count the number of virtual functions and times
4.
Here is my guess:
suppose we want to know the vtable size of class B.
build D,
class D : public B
{
virtual void test(){}
};
now, in the memory:
D:
+0: pointer to vtable
vtabble:
... v functions in class B
test()
D * pd= new D;
void (*p)()=pd->test;
char * vtable_base=(char *)(*(int *)pd);
vsize=(char *)p - vtable_base;
4.
Here is my guess:
suppose we want to know the vtable size of class B.
build D,
class D : public B
{
virtual void test(){}
};
now, in the memory:
D:
+0: pointer to vtable
vtabble:
... v functions in class B
test()
D * pd= new D;
void (*p)()=pd->test;
char * vtable_base=(char *)(*(int *)pd);
vsize=(char *)p - vtable_base;
t*t
3 楼
看上去很不错,写成template就更牛了
times
【在 c****e 的大作中提到】
: Statically, I think you can count the number of virtual functions and times
: 4.
: Here is my guess:
: suppose we want to know the vtable size of class B.
: build D,
: class D : public B
: {
: virtual void test(){}
: };
: now, in the memory:
times
【在 c****e 的大作中提到】
: Statically, I think you can count the number of virtual functions and times
: 4.
: Here is my guess:
: suppose we want to know the vtable size of class B.
: build D,
: class D : public B
: {
: virtual void test(){}
: };
: now, in the memory:
d*d
4 楼
times
~~~~~~~
有一点不明白的，请问这里是为什么。
【在 c****e 的大作中提到】
: Statically, I think you can count the number of virtual functions and times
: 4.
: Here is my guess:
: suppose we want to know the vtable size of class B.
: build D,
: class D : public B
: {
: virtual void test(){}
: };
: now, in the memory:
c*g
5 楼
1. the layout of the object and vtable in memory depends on compiler
implementation
2. you cannot get # of v functions at runtime
3. times by 4 depends on platforms
4. how about multiple inheritence?
.....
times
【在 c****e 的大作中提到】
: Statically, I think you can count the number of virtual functions and times
: 4.
: Here is my guess:
: suppose we want to know the vtable size of class B.
: build D,
: class D : public B
: {
: virtual void test(){}
: };
: now, in the memory:
implementation
2. you cannot get # of v functions at runtime
3. times by 4 depends on platforms
4. how about multiple inheritence?
.....
times
【在 c****e 的大作中提到】
: Statically, I think you can count the number of virtual functions and times
: 4.
: Here is my guess:
: suppose we want to know the vtable size of class B.
: build D,
: class D : public B
: {
: virtual void test(){}
: };
: now, in the memory:
t*t
6 楼
this is of course implementation defined... the standard doesn't even say
there exists a vtable or vptr.
but,
1. layout of the object is implementation defined, but *usually* vptr is the
first entry.
2. ???
3. you can use sizeof(any_pointer_to_function) instead.
4. this is indeed a big problem.
【在 c*****g 的大作中提到】
: 1. the layout of the object and vtable in memory depends on compiler
: implementation
: 2. you cannot get # of v functions at runtime
: 3. times by 4 depends on platforms
: 4. how about multiple inheritence?
: .....
:
: times
there exists a vtable or vptr.
but,
1. layout of the object is implementation defined, but *usually* vptr is the
first entry.
2. ???
3. you can use sizeof(any_pointer_to_function) instead.
4. this is indeed a big problem.
【在 c*****g 的大作中提到】
: 1. the layout of the object and vtable in memory depends on compiler
: implementation
: 2. you cannot get # of v functions at runtime
: 3. times by 4 depends on platforms
: 4. how about multiple inheritence?
: .....
:
: times
c*x
7 楼
http://en.wikipedia.org/wiki/Virtual_table
【在 z***e 的大作中提到】
: Is there any way to get vptr or check the size of virtual function table?
: thx.
c*g
8 楼
2.是说：程序运行的时候没法知道到底一个object有几个virtual functions。如果
class里virtual function改变了，其他的code相应地都得变。
the
【在 t****t 的大作中提到】
: this is of course implementation defined... the standard doesn't even say
: there exists a vtable or vptr.
: but,
: 1. layout of the object is implementation defined, but *usually* vptr is the
: first entry.
: 2. ???
: 3. you can use sizeof(any_pointer_to_function) instead.
: 4. this is indeed a big problem.
class里virtual function改变了，其他的code相应地都得变。
the
【在 t****t 的大作中提到】
: this is of course implementation defined... the standard doesn't even say
: there exists a vtable or vptr.
: but,
: 1. layout of the object is implementation defined, but *usually* vptr is the
: first entry.
: 2. ???
: 3. you can use sizeof(any_pointer_to_function) instead.
: 4. this is indeed a big problem.
c*g
9 楼
原来有typo，cannot中not漏了。
【在 c*****g 的大作中提到】
: 2.是说：程序运行的时候没法知道到底一个object有几个virtual functions。如果
: class里virtual function改变了，其他的code相应地都得变。
:
: the
【在 c*****g 的大作中提到】
: 2.是说：程序运行的时候没法知道到底一个object有几个virtual functions。如果
: class里virtual function改变了，其他的code相应地都得变。
:
: the
p*o
10 楼
Well, it's doable if you can change the code and ask others to follow you,
e.g. get a virtual function to allow query such information like COM,
or have a compiler giving such information like Java ...
Otherwise, it's too hard. Do we have any reflection library for C++ now?
【在 c*****g 的大作中提到】
: 2.是说：程序运行的时候没法知道到底一个object有几个virtual functions。如果
: class里virtual function改变了，其他的code相应地都得变。
:
: the
e.g. get a virtual function to allow query such information like COM,
or have a compiler giving such information like Java ...
Otherwise, it's too hard. Do we have any reflection library for C++ now?
【在 c*****g 的大作中提到】
: 2.是说：程序运行的时候没法知道到底一个object有几个virtual functions。如果
: class里virtual function改变了，其他的code相应地都得变。
:
: the
W*g
11 楼
不可行。首先vptr在哪不清楚，微软是放在前面，但是更直接的方法是在后面，如果是
这样，对于derived class来说vptr就在中间了，这还没有考虑multiple inherit（多
个vtbl） 和virtual inherit（virtual base class有自己的vtbl）。
其次vtbl里还有其他东西，比如typeid。有些实现会把this pointer adjustment
offsets放在vtbl里。
这样，对于derived class来说vptr就在中间了，这还没有考虑multiple inherit（多
个vtbl） 和virtual inherit（virtual base class有自己的vtbl）。
其次vtbl里还有其他东西，比如typeid。有些实现会把this pointer adjustment
offsets放在vtbl里。
相关阅读
求推荐个 ACH payment gateway apigolang 的50个坑，初级到中级stackoverflow 2015 用户调查Deepmind，蜘蛛坦克，小笼包(zz)一个用java写spark应用的问题java 这种破烂语言做的产品真心维护难 (转载)请推荐perl web framework有dynamo大牛吗？Backbone 还是angular继续掐12306FLAG这些公司招码农会查信用记录吗？请问怎样打开一个有密码的Access数据库 (转载)菜鸟来了 怎么比较一个modernizr到另一个modernizrgo 的坑（转载）wdong和赵老师请进question on javascript stream做一个网站，把其他网站地址列表拉出来在地图上显示,怎么做?并联100只猩猩, 能不能过图灵测试? (转载)DeepMind创始人自述：我们的算法可以横扫一切棋类博弈古德霸走了，赵策也不来了