C ++：如何获取指向二维动态数组的指针？

Question

I looked at this excellent answer but can't figure out how to apply it to this snipped:

//this is in the .hpp file
std::atomic<int> size = 10;
std::recursive_mutex *locks[2];

//in some function of the class
//it's important that the 2nd array dimension is dynamic
the_lock[0] = new std::recursive_mutex[size]; 
the_lock[1] = new std::recursive_mutex[size];
std::recursive_mutex (*locks_2)[2][size] = &locks;

The assignment gives me

error: cannot convert ‘std::recursive_mutex* (*)[2]’ to ‘std::recursive_mutex (*)
[2][(((sizetype)(((ssizetype)((**here be long type information, since I'm using
templates a lot**, long unsigned int, std::less<long unsigned int>          
>::size.std::atomic<long unsigned 
int>::<anonymous>.std::__atomic_base<_IntTp>::operator 
std::__atomic_base<_IntTp>::__int_type<long unsigned int>()) + -1)) + 1)]’ in 
initialization

How can I obtain a pointer to 'locks'?

Answer 1

错误消息实际上是免费提供解决方案的：

std::recursive_mutex * (*locks_2)[2] = &locks;

Answer 2

One can use the fact that this sort of thing has been officially declared to be ridiculously hard to get right for no apparent reason that the compiler cannot solve for you. If your compiler supports C++ 2011 that is. Use:

auto my_ptr = &locks; // point to locks, let the compiler worry about types

Requires that you compile your code as C++ 2011 though. ( -std=c++11 for GCC).

Answer 3

locks is just an array of pointers. So you could use a pointer pointer to point to it.

std::recursive_mutex **locks_2 = locks;