Question

在下面的简化代码中，我有一个具有两个属性的类，我需要根据另一个的值更改一个而不更改第二个的值。我不想创建一个新的临时变量来做它（我不想分配新内存并清除旧内存），我需要使用指针

#include<iostream>

using namespace std;

class A{

private:

int **m1;
int **m2;

void allocate_mem(int ***ptr){
    *ptr = new int*[1];
    (*ptr)[0] = new int[1];
}

public:

A(){
    allocate_mem(&m1);
    m1[0][0] = 1;
    allocate_mem(&m2);
    m2[0][0] = 1;
}

//I need a method that change m2 (according to the value of m2) without changhig the value of m2
//this following doesn't work
A renew(){
    if(m1[0][0]>0)
        m2[0][0] = 1000;
}

~A(){
    delete[] m1[0];
    delete[] m1;
    delete[] m2[0];
    delete[] m2;    
}

void create_output(){
    cout << m1[0][0] << endl << m2[0][0] << endl;
}

};

Answer 1

将A renew()更改为void renew()，代码可以正常运行。

#include<iostream>
using namespace std;

class A{
private:

int **m1;
int **m2;

void allocate_mem(int ***ptr){
    *ptr = new int*[1];
    (*ptr)[0] = new int[1];
}

public:

A(){
    allocate_mem(&m1);
    m1[0][0] = 1;
    allocate_mem(&m2);
    m2[0][0] = 1;
}

//I need a method that change m2 (according to the value of m1) without changhig the value of m1
void renew(){
    if(m1[0][0]>0)
        m2[0][0] = 1000;
}

~A(){
    delete[] m1[0];
    delete[] m1;
    delete[] m2[0];
    delete[] m2;
}

void create_output(){
    cout << m1[0][0] << endl << m2[0][0] << endl;
}

};

int main(){
  A mat;
  mat.create_output();
  mat.renew();
  mat.create_output();

  return 0;
}

这会产生：

c ++类的两个动态属性

1 个答案: