void* 和 void** 的心智模型？
注意：我是一名经验丰富的 C++ 程序员，因此我不需要任何指针基础知识。只是我从未使用过 void** 并且很难将我的心理模型调整为 void* 与 void** >。我希望有人能以一种好的方式解释这一点，以便我可以更容易地记住语义。
考虑以下代码：（使用 VC++ 2005 等进行编译）
int main() {
int obj = 42;
void* ptr_to_obj = &obj;
void* addr_of_ptr_to_obj = &ptr_to_obj;
void** ptr_to_ptr_to_obj = &ptr_to_obj;
void* another_addr = ptr_to_ptr_to_obj[0];
// another_addr+1; // not allowed : 'void*' unknown size
ptr_to_ptr_to_obj+1; // allowed
}
Note: I'm a experienced C++ programmer, so I don't need any pointer basics. It's just that I never worked with void** and have kind of a hard time getting my mental model adjusted to void* vs. void**. I am hoping someone can explain this in a good way, so that I can remember the semantics more easily.
Consider the following code: (compiles with e.g. VC++ 2005)
int main() {
int obj = 42;
void* ptr_to_obj = &obj;
void* addr_of_ptr_to_obj = &ptr_to_obj;
void** ptr_to_ptr_to_obj = &ptr_to_obj;
void* another_addr = ptr_to_ptr_to_obj[0];
// another_addr+1; // not allowed : 'void*' unknown size
ptr_to_ptr_to_obj+1; // allowed
}
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void*是一个指向某个东西的指针，但你不知道是什么。因为你不知道它是什么，也不知道它占用了多少空间，所以你不能递增指针。void**是一个指向void*的指针，因此它是一个指向指针的指针。我们知道空间指针占用了多少空间，因此我们可以增加void**指针以指向下一个指针。void*is a pointer to something, but you don't know what. Because you don't know what it is, you don't know how much room it takes up, so you can't increment the pointer.void**is a pointer tovoid*, so it's a pointer to a pointer. We know how much room pointers take up, so we can increment thevoid**pointer to point to the next pointer.void*指向编译器未知其类型的对象。void**指向存储这样一个void*的变量。A
void*points to an object whose type is unknown to the compiler.A
void**points to a variable which stores such avoid*.void *可以指向任何东西（函数除外）。所以它甚至可以指向指针，因此它甚至可以指向其他void *对象。void **是一个指向void *的指针，因此它只能用于指向void *对象。A
void *can point at anything (except functions). So it can even point at pointers, so it can even point at othervoid *objects.A
void **is a pointer-to-void *, so it can only be used to point atvoid *objects.void具有误导性，因为它听起来像null。但是，最好将void视为未指定的类型。因此，void*是未指定类型的指针，void**是指向未指定类型的指针。voidis misleading because it sounds likenull. However, it's better to think ofvoidas an unspecified type. So avoid*is pointer for an unspecified type, and avoid**is a pointer to a pointer for an unspecified type.void是一种没有对象的类型。void *是传统的标量类型。void **也是一种传统的标量类型，恰好指向void *。void *可以用来指向任何东西，但我更喜欢只将它用于未初始化的存储。通常有更好的替代方法来将void *指向实际对象。voidis a type which has no objects.void *is a conventional scalar type.void **is also a conventional scalar type that happens to point tovoid *.void *can be used to point to anything, but I prefer to use it only for uninitialized storage. There is usually a better alternative to pointing avoid *at an actual object.