指向固定大小数组的指针数组 [英] Array of pointers to an array of fixed size

问题描述

我试图将两个固定大小的数组分配给指向它们的指针数组，但编译器警告我，我不明白为什么.

I tried to assign two fixed-size arrays to an array of pointers to them, but the compiler warns me and I don't understand why.

int A[5][5];
int B[5][5];
int*** C = {&A, &B};

此代码编译时出现以下警告:

This code compiles with the following warning:

警告:从不兼容的指针类型初始化[默认启用]

warning: initialization from incompatible pointer type [enabled by default]

如果我运行代码，它将引发分段错误.但是，如果我动态分配 A 和 B，它工作得很好.这是为什么?

If I run the code, it will raise a segmentation fault. However, if I dynamically allocate A and B, it works just fine. Why is this?

推荐答案

如果您想要一个符合 A 和 B 的现有声明的 C 声明 你需要这样做:

If you want a declaration of C that fits the existing declarations of A and B you need to do it like this:

int A[5][5];
int B[5][5];
int (*C[])[5][5] = {&A, &B};

C 的类型读作C 是一个指向 int [5][5] 数组的指针数组".由于无法分配整个数组，因此需要为该数组分配一个指针.

The type of C is read as "C is an array of pointers to int [5][5] arrays". Since you can't assign an entire array, you need to assign a pointer to the array.

通过这个声明，(*C[0])[1][2] 访问与 A[1][2] 相同的内存位置.

With this declaration, (*C[0])[1][2] is accessing the same memory location as A[1][2].

如果你想要像 C[0][1][2] 这样更简洁的语法，那么你需要做其他人所说的并动态分配内存:

If you want cleaner syntax like C[0][1][2], then you would need to do what others have stated and allocate the memory dynamically:

int **A;
int **B;
// allocate memory for A and each A[i]
// allocate memory for B and each B[i]
int **C[] = {A, B};

您也可以使用来自莫斯科的 Vlad 建议的语法来执行此操作:

You could also do this using the syntax suggested by Vlad from Moscow:

int A[5][5];
int B[5][5];
int (*C[])[5] = {A, B};

C 的这个声明被读作C 是一个指向 int [5] 数组的指针数组".在这种情况下，C的每个数组元素的类型都是int(*)[5]，类型是int [5][5]的数组代码>可以衰减到这种类型.

This declaration of C is read as "C is an array of pointers to int [5] arrays". In this case, each array element of C is of type int (*)[5], and array of type int [5][5] can decay to this type.

现在，您可以使用 C[0][1][2] 访问与 A[1][2] 相同的内存位置.

Now, you can use C[0][1][2] to access the same memory location as A[1][2].

这个逻辑也可以扩展到更高的维度:

This logic can be expanded to higher dimensions as well:

int A[5][5][3];
int B[5][5][3];
int (*C[])[5][3] = {A, B};

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