[英]C++ vector storing base class pointers
Ok, situation: I am using a library that I have no control over, which has a method createSomeObject(). 好的,情况:我使用的是一个我无法控制的库,它有一个方法createSomeObject()。 This method returns a pointer to an abstract base class with pure virtual functions, and it has no copy constructor so I can't instantiate it myself nor copy it (obviously).
这个方法返回一个指向具有纯虚函数的抽象基类的指针,它没有复制构造函数,所以我不能自己实例化它,也不能复制它(显然)。
I need to store some number (let's say 10) of these in a vector, so I tried to do the following: 我需要在向量中存储一些数字(比如说10个),所以我尝试执行以下操作:
vector<AbstractBaseClass*> v(10);
for(int i = 0; i < 10; i++)
{
v.push_back(library->createSomeObject());
}
As soon as this loop is over, the vector is filled with broken pointers. 一旦这个循环结束,向量就会被破碎的指针填充。
I have tried the following: 我尝试过以下方法:
vector<AbstractBaseClass*> v(10);
for(int i = 0; i < 10; i++)
{
AbstractBaseClass* abc = library->createSomeObject();
v.push_back(abc);
}
To no avail. 无济于事。 I must be going crazy or doing something seriously wrong here.
我必须疯狂或在这里做一些严重的错误。 I've looked around but the answer is always use boost::shared_ptr.
我环顾四周,但答案总是使用boost :: shared_ptr。 A great solution possibly, but I can't guarantee that it'll be on the machines that this will be built on, so I'd like to avoid packaging Boost with the code.
可能是一个很好的解决方案,但是我不能保证它将会在这些将被构建的机器上,所以我想避免使用代码包装Boost。
Is there something I'm missing? 有什么我想念的吗? I feel as though I'm just forgetting some simple thing, as I can't think of a reason one of these wouldn't work.
我觉得好像忘记一些简单的事情,因为我无法想到其中一个不起作用的原因。
When you do this: 当你这样做:
vector<AbstractBaseClass*> v(10);
you're already creating a vector which contains 10 (NULL) pointers. 你已经在创建一个包含10个(NULL)指针的向量。 So after you've called
push_back
, you'll have a vector with 20 pointers, out of which the first 10 are invalid. 因此,在你调用
push_back
,你将拥有一个包含20个指针的向量,其中前10个指针无效。
If you know the size beforehand: 如果您事先知道尺寸:
vector<AbstractBaseClass*> v(10);
for(int i = 0; i < 10; i++)
{
v[i] = library->createSomeObject();
}
or, alternitively, call reserve
after creating an empty vector. 或者,可选地,在创建空向量之后调用
reserve
。
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