c - 编译器是否应该对带有 void 指针的指针算法发出警告？

Question

我正在使用 gcc 4.7.2 编译 C 程序。我有一个 void * 类型的地址和一些偏移量。 (void* + size) 应该给出警告。如果不是，那么如果大小为 1 和大小为 50，它将添加多少字节。我唯一关心的是应该警告我们正在向 void 指针添加一些东西吗？

 12         int size = 50;
 /*Allocate a block of memory*/
 14         void *BlockAddress   = malloc(200);
 15         if(!BlockAddress)
 16                  return -1;
 17         address1             = (int *)BlockAddress;
 18         address2             = BlockAddress + 1*size;
 19         address3             = BlockAddress + 2*size;

谢谢

Answer 1

你不应该对 void 指针进行指针运算。

来自 C 标准

6.5.6-2: For addition, either both operands shall have arithmetic type, or one operand shall be a pointer to an object type and the other shall have integer type.

6.2.5-19: The void type comprises an empty set of values; it is an incomplete type that cannot be completed.

GNU C 通过考虑 void 的大小为 1 来允许上述操作。

来自 6.23 Arithmetic on void- and Function-Pointers :

In GNU C, addition and subtraction operations are supported on pointers to void and on pointers to functions. This is done by treating the size of a void or of a function as 1.

所以按照上面的几行我们得到:

 address2             = BlockAddress + 1*size; //increase by 50 Bytes
 address3             = BlockAddress + 2*size; //increase by 100 Bytes