如何更改指向向量的指针的元素？

Question

假设我有几个整数向量和一个指向整数向量的指针。我将如何将指针的一个元素的值更改为其他整数向量之一中的地址？

背景是我已经构建了一个类，可以让我将桌面引入虚幻引擎，但是在每个滴答声中，它必须将包含结构的向量形式分配给另一个数据类的值每次滴答，我希望只复制几个元素（像素颜色值）的内存地址，这样我就不必浪费时间复制两次（对于桌面图像来说，这是数百万次操作）

#include <iostream>
#include <vector>

using namespace std;

// Print function
void PrintVector(vector<int> v)
{
 for( int i = 0; i < v.size(); i++ )
 {
 cout << v[i] << ", ";
 }
 cout << endl;
}

int main()
{

    vector<int> vector1;
    vector<int> vector2;
    vector<int> *ptrvector;

    //Do some assignment so the vectors have values
    for( int i = 0; i<3; i++)
    {
        vector1.push_back(i);
        vector2.push_back(2*i);
    }
    //Assign the pointer to the address of vector1.
    ptrvector = &vector1;

    //Print out:
    PrintVector(vector1);  // (1,2,3)
    PrintVector(vector2);  // (2,4,6)
    PrintVector(*ptrvector); // (1,2,3)
    // We should see that lines 1 and 3 are the same

    //BROKEN BIT::

    //Ideally want something like
    ptrvector[0] = &vector2[2];
    PrintVector(*ptrvector); // (6,2,3);

    //Such that if I were to do this:
    vector2[2] = 20;
    PrintVector(*ptrvector); // It should change as a side effect: (20,2,3)


}

额外问题：

假设我有这个：

TArray<FColor> ColorData;
TArray<FColor> *ptrColorData
//Where TArray is essentially a vector. FColor is a struct with members (R,G,B,A)

//ColorData is initialised somewhere and we set the ptrColorData to the address
ptrColorData = &ColorData;

//Somewhere down the line we have a long loop whereby we do
ColorData[i].B = somedata[i];
ColorData[i].G = somedata[i+1];
ColorData[i].R = somedata[i+3];

//somedata is updated per tick, asigning ColorData per tick as well slows it down.
// I wish to be able to do something on the lines of this

ptrColorData[i].B = &somedata[i];
ptrColorData[i].G = &somedata[i+1];
ptrColorData[i].R = &somedata[i+3];

// this is only called once to initialize. Because the memory address
//is unchanging and somedata changes by functions on its own it means when
// I tell my unreal engine to update a texture by passing (*ptrColorData)
// to a function it automatically has the new data when that function is
// next called.

Answer 1

这应该会产生您想要的输出，但请注意。如 cmets 所述，如果您以任何方式更改 vector1 或 vector2 的大小并且重新排序原始向量中的元素，则存储在 std::vector<int*> 中的地址应被视为无效，您的指针将指向错误的价值观。我还删除了using namespace std;。请参阅：Why is “using namespace std” considered bad practice?。

#include <iostream>
#include <vector>

// Print function
void PrintVector(std::vector<int> v) {
    for(auto x : v) std::cout << x << ", ";
    std::cout << "\n";
}

void PrintVector(std::vector<int*> v) {
    for(auto x : v) std::cout << *x << ", ";
    std::cout << "\n";
}

int main() {
    std::vector<int> vector1;
    std::vector<int> vector2;
    std::vector<int*> ptrvector; // pointers to the elements in vector1/2

    //Do some assignment so the vectors have values
    for( int i = 1; i<=3; i++) {
        vector1.push_back(i);
        vector2.push_back(2*i);
    }
    // Add pointers in ptrvector to the addresses in vector1.
    ptrvector.reserve(vector1.size());
    for(auto& r : vector1)
        ptrvector.emplace_back(&r);

    //Print out:
    PrintVector(vector1);   // (1,2,3)
    PrintVector(vector2);   // (2,4,6)
    PrintVector(ptrvector); // (1,2,3)

    ptrvector[0] = &vector2[2];
    PrintVector(ptrvector); // (6,2,3);

    vector2[2] = 20;
    PrintVector(ptrvector); // (20,2,3)
}