关于C++中const指针的问题？

Question

我无法解释自己以下代码:

   double d = 100;

    double const d1 = 30;

    double* const p = &d; // Line 1
    double* const p1 = &d1; // Line 2

在上面的代码中,没问题Line 1,但Line 2产生错误:

"error C2440: 'initializing' : cannot convert from 'const double *__w64 ' to 'double *const '"

有人可以详细说明吗？(我使用的是VS C++ 2005,在Win XP SP3上运行)

Answer 1

该类型double* const是一个指向非const double的const指针.如果你想要一个指向const double的指针,你必须使用double const*(或者double const* const你想要一个指向const double的const指针).

在C++中,使用一个指向double的简单指针,你既可以指示指针本身(也就是说,它可以使它指向另一个位置)和值的常量(可以通过指针改变值)吗？ )可以独立配置.这为您提供了四种非常相似但不兼容的类型:

double const* const p1; // Const pointer to const double
                        //  . you can't have the pointer point to another address
                        //  . you can't mutate the value through the pointer

double const* p2;       // Non-const pointer to const double
                        //  . you can have the pointer point to another address
                        //  . you can't mutate the value through the pointer

double* const p3;       // Const pointer to double
                        //  . you can't have the pointer point to another address
                        //  . you can mutate the value through the pointer

double* p4;             // Non-const pointer to non-const double
                        //  . you can have the pointer point to another address
                        //  . you can mutate the value through the pointer