受限制的指针分配

Question

我有一个关于受限指针分配的问题。具体问题请参见代码中的注释。总的来说，我只是想知道限制的合法性（我已阅读标准，但仍有疑问:-(

int* Q = malloc(sizeof(int)*100);

{
    int* restrict R = Q;

    for(int j = 0; j < rand()%50; j++)
    {
        R[j] = rand();
    }

    Q = R; // The standard says assigning restricted child pointers to their parent is illegal.
           // If Q was a restricted pointer, is it correct to assume that this would be ILLEGAL?
           //
           // Since Q is unrestricted, is this a legal assignment?
           //
           // I guess I'm just wondering: 
           // What's the appropriate way to carry the value of R out of the block so
           // the code can continue where the above loop left off? 
}

{
    int* S = Q;   // unrestricted child pointers, continuing where R left off above
    int* T = Q+1; // S and T alias with these assignments

    for(int j = 0; j < 50; j++)
    {
        S[j] = T[j];
    }
}

感谢您的帮助！

Answer 1

由于正在修改的对象（在第一行分配的数组）不会通过左值表达式进行修改，除非涉及声明 R 的块中的受限指针 R，我认为您的示例中的代码定义良好。

如果 Q 是受限制的指针，则该示例将是未定义的。