[英]Dereferencing an array of void pointers
Say I have an array of void pointer pointing to objects of different types and I want to pass them through a function and cast them to pointers of their respective type, how would I go about doing this? 假设我有一个指向不同类型对象的void指针数组,我想通过一个函数传递它们并将它们转换为各自类型的指针,我将如何进行此操作? I've tried this current code, but I get error:
我已经尝试过这个当前代码,但是我收到错误:
'void*' is not a pointer-to-object type
'void *'不是指向对象的指针类型
objectA myObjectA;
objectB myObjectB;
objectC myObjectC;
objectD myObjectD;
void *data[4];
data[0] = static_cast<void *>( &myObjectA );
data[1] = static_cast<void *>( &myObjectB );
data[2] = static_cast<void *>( &myObjectC );
data[3] = static_cast<void *>( &myObjectD );
void dereference( void *data )
{
objectA *objA_ptr = static_cast<objectA *>( data[0] );
objectB *objB_ptr = static_cast<objectB *>( data[1] );
objectC *objC_ptr = static_cast<objectC *>( data[2] );
objectD *objD_ptr = static_cast<objectD *>( data[3] );
}
Anyone know the correct way to implement this? 有谁知道实现这个的正确方法?
edit: For context, I'm using opencv and trying to create a simple gui interface with a trackbar. 编辑:对于上下文,我正在使用opencv并尝试使用轨迹栏创建一个简单的gui界面。 Opencv allows for userdata to be fed into the TrackbarCallback which is called when the slider is moved, but only in the form of a void pointer.
Opencv允许将userdata输入到TrackbarCallback中,当移动滑块时调用它,但只能以void指针的形式调用。
int createTrackbar( const string& trackbarname, const string& winname,
int* value, int count,
TrackbarCallback onChange=0,
void* userdata=0);
Say I have an array of void pointer
假设我有一个void指针数组
void deference( void *data )
That's not an array of void pointers, it's a single void pointer. 这不是一个void指针数组,它是一个单独的void指针。
Change that to void **
, and then since you're mixing C and C++ styles up anyway, why not just use a C style cast? 将其更改为
void **
,然后因为你要混合使用C和C ++样式,为什么不使用C样式转换呢? : :
objectA *objA_ptr = (objectA *) data[0];
Derive them all from the same base class. 从同一个基类派生所有这些。
make the destructors virtual if your function needs to delete them. 如果您的函数需要删除它们,则将析构函数设置为虚拟。
make your array BaseClass *data[4]
使你的数组
BaseClass *data[4]
make your function void deference(BaseClass **data)
使你的函数
void deference(BaseClass **data)
您可以使用reinterpret_cast<>()
而不是static_cast<>
。
The correct function prototype needs to be 需要正确的函数原型
void dereference(void **data)
since you're passing an array of void *
, and as we all know in C and C++ an array expression is replaced with a pointer expression in most circumstances. 因为你传递的是一个
void *
数组,而且我们都知道在C和C ++中,在大多数情况下,数组表达式会被指针表达式替换。
Is there any particular reason why you must use an array of pointers to objects of differing classes? 是否有任何特殊原因必须使用指向不同类对象的指针数组? This smells like a C solution to a C++ problem.
这闻起来像是C ++问题的C解决方案。
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