[英]c++ aliasing pointer of dynamic dimensional array
I am working on multidimensional arrays.我正在研究多维 arrays。 The matrix's data and dimensions are given during runtime, and I tried to access the data with type alias pointer such as below.
矩阵的数据和维度是在运行时给出的,我尝试使用类型别名指针访问数据,如下所示。
It worked well with my code, but I am not sure if it's within c++ standard.它适用于我的代码,但我不确定它是否符合 c++ 标准。
Can I use type alias like this: unknown-dimensional array pointer?我可以使用这样的类型别名:未知维数组指针吗?
cin >> a; //1
cin >> b; //2
cin >> c; //3
int* buf = new int[100]; //just to allocate some memory for test
using arr_t = int (*)[a][b][c]; //type alias of pointer of array
arr_t arr = reinterpret_cast<arr_t>(buf);
buf[3] = 1;
cout << arr[0][1][0] << endl; // 1 (It's easier than buf[b*c*0 + c*1 + 0])
cout << (void*)&buf[3] << endl; //0x18b8e78
cout << (void*)&(*arr)[0][1][0] << endl; //0x18b8e78
int (*)[a][b][c]
with runtime values uses VLA (Variable Length Array) extension, and so, is not standard C++.具有运行时值
int (*)[a][b][c]
使用 VLA(可变长度数组)扩展,因此不是标准的 C++。
And even with that extension, your cast breaks strict aliasing rules.即使有了这个扩展,你的演员也打破了严格的别名规则。
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