c++ - Const 和非常量 C++ 构造函数

Question

在 C++03(或更早版本)中是否有一种方法可以编写一个可以存储 const 或非 const 指针并适当处理访问的类？以非功能性“SometimesConst”类的用法为例:

class SometimesConst
{
    public:
    SometimesConst(int * buffer) : buffer(buffer) {} // Needs const qualifier?

    int* get() { return buffer; } // Needs const qualifier?

    void increment() { counter++; }

    private:
    int * buffer; // Needs const qualifier?
    int counter;
};

void function(int * n, const int * c)
{
    // These are both okay
    SometimesConst wn(n);
    SometimesConst wc(c);

    // Reading the value is always allowed
    printf("%d %d", wn.get()[0], wc.get()[0]);

    // Can increment either object's counter
    wn.increment();
    wc.increment();

    // Can set non-const pointer
    wn.get()[0] = 5;

    // Should generate a compiler error
    wc.get()[0] = 5;
}

创建常量 SometimesConst 不允许修改对象的计数器属性。是否可以设计一个对输入对象具有编译时常量安全性的类，前提是它们作为常量传入？

Answer 1

不，不是您想要的使用方式。在编译时具有不同行为的唯一方法是具有不同的类型。但是，您可以使其相当易于使用:

#include <stdio.h>

template <typename T>
class SometimesConst
{
  public:
    SometimesConst(T* buffer) : buffer(buffer) { }
    T* get() { return buffer; }
    void increment() { ++counter; }
  private:
    T *buffer;
    int counter;
};

typedef SometimesConst<const int> IsConst;
typedef SometimesConst<int> IsNotConst;

void function(int * n, const int * c)
{
  IsNotConst wn(n);
  IsConst wc(c);

  // Reading the value is always allowed
  printf("%d %d", wn.get()[0], wc.get()[0]);

  // Can increment either object's counter
  wn.increment();
  wc.increment();

  // Can set non-const pointer
  wn.get()[0] = 5;

  // Should generate a compiler error
  wc.get()[0] = 5;
}