Polymorphism amp; Pointers to arrays(多态性与指向数组的指针)
问题描述
I have a class A:
class A
{
public:
virtual double getValue() = 0;
}
And a class B:
class B : public A
{
public:
virtual double getValue() { return 0.0; }
}
And then in main() I do:
A * var;
var = new B[100];
std::cout << var[0].getValue(); //This works fine
std::cout << var[1].getValue(); //This, or any other index besides 0, causes the program to quit
If instead I do:
B * var;
var = new B[100];
std::cout << var[0].getValue(); //This works fine
std::cout << var[1].getValue(); //Everything else works fine too
Everything compiles fine, but it seems as though there is something wrong with my polymorphism perhaps? I'm puzzled.
You can't treat arrays polymorphically, so while new B[100]
creates an array of B
objects and returns a pointer to the array - or equivalently the first element of the array - and while it is valid to assign this pointer to a pointer to a base class, it is not valid to treat this as a pointer into an array of A
objects.
The principal reason that you can't is that (typically) derived objects are a different size to their base classes, so attempting to access the array as an array of base class objects will not use the correct offset to get a pointer to the next base class subobject of the next member of the derived class array.
这篇关于多态性与指向数组的指针的文章就介绍到这了,希望我们推荐的答案对大家有所帮助,也希望大家多多支持编程学习网!
本文标题为:多态性与指向数组的指针
基础教程推荐
- \a序列表示“钟”字符。 1970-01-01
- 使用基本数据类型,并输出它们的值,int,floa 1970-01-01
- C++ #define 1970-01-01
- C语言库difftime()函数 1970-01-01
- C++函数调用运算符()重载 1970-01-01
- C++条件编译 1970-01-01
- 读取名字和身高并显示信息 1970-01-01
- C++递增指针 1970-01-01
- C++ - 指向对象的向量的性能与对象的性能 2022-10-18
- 使用printf()显示int类型的变量 1970-01-01