在用c ++中的文件读取后，对“动态”列进行排序。

Question

文本文件例如包含15列数据，但只有三列（列）对于进一步计算很重要。现在我想通过 ifstream 读取所有列，然后创建一个只包含重要列的新文件（在本例中为3）。

std::vector<double> column1;        
std::vector<double> column2;        
std::vector<double> column3;

double col1;
double col2;
double col3;

double sortCol1;
double sortCol2;
double sortCol3;

void readingFile()
{
    // at very first the user is able to see the data of the file and decide which columns are needed. 
    std::cout << "Which columns do you need?" << std::endl;
    std::cin >> col1;  // for example column 3
    std::cin >> col2;  // column 5
    std::cin >> col3;  // and column 9

    std::ifstream file("testFile.txt"); //reading the file
    if(!file)                         
    {
        std::cerr << "* Can't open file! *" << std::endl;
    }
    else
    {   // this is the point which i don't get. 
        // How do i specify "dynamic" which column i need?
        // somethimes i need to pushback sortCol7 to column1 sometimes sortCol3 to column1 and so on. 
        while(file >> sortCol1 >> sortCol2 >> sortCol3 ... and so on...)
        {
            // i think i need an if-statement here with conditions like: 
            // col x = sortCol x 
            column1.push_back(sortCol1);
            column2.push_back(sortCol2);
            column3.push_back(sortCol3);
        }
    }
    file.close();
}

重要的是要知道数据文件的格式是可变的。所以我不能写一个静态代码，每次在同一个向量中推送相同的列。