C++ 循环遍历对象的地址

Question

对象（非动态）是内存中的数据块。

有没有办法循环打印对象中的每个项目？

我尝试使用“this”来执行此操作，但我不断收到错误。

#include "stdafx.h"
#include <iostream>
#include "TestProject.h"

using namespace std;


class myclass {

    int someint = 10;
    double somedouble = 80000;
    int somearray[5] = {0, 1, 2, 3, 4};


public:   
    void somefunction();


};


void myclass::somefunction() {


    cout << "\n test \n" << this;

    myclass *somepointer;

    somepointer = this; 

    somepointer += 1;

    cout << "\n test2 \n" << *somepointer;
    //Error: no opperator '<<' matches these operands

}



int main() {


    myclass myobject;

    myobject.somefunction();

    return 0;
}

我猜这个错误是因为类型不匹配。但我真的想不出解决办法。是否有动态类型，或者我必须以某种方式测试类型？

Answer 1

你必须添加好友全局std::ostream operator <<才能显示对象的内容

#include "stdafx.h"
#include <iostream>

using namespace std;


class myclass {
    int someint;
    double somedouble;
    int somearray[5];
public: 
    myclass()
    {
        someint = 10;
        somedouble = 80000;
        somearray[0] = 0;
        somearray[1] = 1;
        somearray[2] = 2;
        somearray[3] = 3;
        somearray[4] = 4;
    }
    void somefunction();
    friend std::ostream& operator << (std::ostream& lhs, const myclass& rhs);
};


std::ostream& operator << (std::ostream& lhs, const myclass& rhs)
{
    lhs << "someint: " << rhs.someint << std::endl
        << "somedouble: " << rhs.somedouble << std::endl
        << "somearray: { ";

    for (int iIndex = 0; iIndex < 5; iIndex++)
    {
        if (iIndex == 4)
            lhs << rhs.somearray[iIndex] << " }" << std::endl;
        else
            lhs << rhs.somearray[iIndex] <<  ", ";
    }

    return lhs;
}


void myclass::somefunction() {


    cout << "\n test \n" << this;

    myclass *somepointer;

    somepointer = this; 

    somepointer += 1; // wrong pointer to object with `object + sizeof(object)` address, 
    // data probably has been corrupted

    cout << "\n test2 \n" << *somepointer; // displaying objects content
}

int main() {


    myclass myobject;

    myobject.somefunction();

    return 0;
}

当你想使用它的指针转移到对象成员时，我发布了另一个程序

#include "stdafx.h"
#include <iostream>

using namespace std;


#pragma pack (push, 1) // force data alignment to 1 byte

class myclass {
    int someint;
    double somedouble;
    int somearray[5];
public: 
    myclass()
    {
        someint = 10;
        somedouble = 80000;
        somearray[0] = 0;
        somearray[1] = 1;
        somearray[2] = 2;
        somearray[3] = 3;
        somearray[4] = 4;
    }
    void somefunction();
    friend std::ostream& operator << (std::ostream& lhs, const myclass& rhs);
};

#pragma pack (pop) // restore data alignment


std::ostream& operator << (std::ostream& lhs, const myclass& rhs)
{
    lhs << "someint: " << rhs.someint << std::endl
        << "somedouble: " << rhs.somedouble << std::endl
        << "somearray: { ";

    for (int iIndex = 0; iIndex < 5; iIndex++)
    {
        if (iIndex == 4)
            lhs << rhs.somearray[iIndex] << " }" << std::endl;
        else
            lhs << rhs.somearray[iIndex] <<  ", ";
    }

    return lhs;
}


void myclass::somefunction() {

    int* pSomeInt = (int*)this; // get someint address
    double *pSomeDouble = (double*)(pSomeInt + 1); // get somedouble address
    int* pSomeArray = (int*)(pSomeDouble + 1); // get somearray address

    std::cout << "someint: " << *pSomeInt << std::endl
        << "somedouble: " << *pSomeDouble << std::endl
        << "somearray: { ";

    for (int iIndex = 0; iIndex < 5; iIndex++)
    {
        if (iIndex == 4)
            std::cout << pSomeArray[iIndex] << " }" << std::endl;
        else
            std::cout << pSomeArray[iIndex] <<  ", ";
    }
}

int main() {


    myclass myobject;

    myobject.somefunction();

    return 0;
}

Answer 2

C++ 在设计上没有反射特性。这意味着在运行时没有通用的、与类型无关的方式来访问类型元数据（例如，如果是类及其类型，则为成员列表）。所以你想要做的事情（如果我理解正确的话）不能在 C++ 中完成。

另外，我不确定您所说的“对象（非动态）”是什么意思。所有对象都是内存中的数据块，无论是否动态分配。