c++ - 标准转换 :Qualification conversions

Question

这是来自 ISO 的要点:标准转换:数组到指针的转换:$4.4:资格转换/第 5 点

    A multi-level pointer to member type, or a multi-level mixed pointer and
     pointer to member type has the form:
           cv 0 P 0 to cv 1 P 1 to . . . cv n − 1 P n − 1 to cv n T
    where P i is either a pointer or pointer to member and where T is not a
    pointer type or pointer to member type.

谁能解释一下。如果可能的话，举个例子..该表格的实际含义。任何人都可以详细说明吗？同样..该部分有不同的形式(资格转换)

Answer 1

多级指针是指向指针的指针。

变量通常可以是 const 或 volatile(这些称为 cv-qualifiers)。当你有一个指针时，指向的数据和指针本身都可以有 cv 限定符。当你有一个多级指针时，任何级别都可以有 cv 限定符。

例如:

int i1 = 1;
const int i2 = 2;
int * p1 = &i1; // p1 is a non-constant pointer to a non-constant int
int * const p2 = &i1; // p2 is a constant pointer to a non-constant int
int const * p3 = &i2; // p3 is a non-constant pointer to a constant int
const int * p4 = &i2; // same as p3
int const * const p5 = &i2; // p5 is a constant pointer to a constant int
int * * pp1 = &p1; // non-const pointer to non-const pointer to non-const int
int * * const pp2 = &p1; // const pointer to non-const pointer to non-const int
int * const * pp3 = &p2; // non-const pointer to const pointer to non-const int
int const * * pp4 = &p3; // non-const pointer to non-const pointer to const int
// etc.