C ++编译器错误不能访问类中声明私有成员'的std :: basic_ios＆LT; _Elem，_Traits＆GT;' [英] c++ compiler error cannot access private member declared in class 'std::basic_ios<_Elem,_Traits>'

问题描述

嘿即时得到我认为出错有从阅读其他职位与复制的ofstream变量做，香港专业教育学院试图改变

Hey Im getting an error I think has to do with copying ofstream variable from reading other posts and Ive tried to change

std::ofstream outfil;

到

std::ofstream & outfil;

但我得到的错误

reference value "outfil" requires an initializer

在code是：

#include <algorithm>
#include <fstream>
#include <iostream>
#include <iterator>
#include <sstream>
#include <string>
#include <vector>
#include <cstdlib>

std::vector<double> GetValues_n(const std::vector<std::string>& src, int start, int end)
{
    std::vector<double> ret;
    for(int i = start; i <= end; ++i)
    {
        ret.push_back(std::strtod(src[i].c_str(), nullptr));
    }
    return ret;
}

std::vector<int> GetValues_c(const std::vector<std::string>& src, int start, int end)
{
    std::vector<int> ret;
    for(int i = start; i <= end; ++i)
    {
        ret.push_back(std::atoi(src[i].c_str()));
    }
    return ret;
}

std::vector<double> polycentre(const std::vector<double>&  x,const std::vector<double>&  y,size_t ID)
{
    std::vector<double> C(3, 0);
    std::vector<double> x1(x.size(),0);
    std::vector<double> y1(y.size(),0);
    size_t sizx = x.size();
    size_t sizy = y.size();
    if(sizy != sizx)
    {
        std::cerr << "polycentre inputs not equal length";
    }
    double x0 = x[0];
    double y0 = y[0];
    for(int aa = 1; aa < sizx; ++aa)
    {
        if(x[aa] < x0){x0 = x[aa];}
        if(y[aa] < y0){y0 = y[aa];}
    }
    double A = 0.0;
    double B = 0.0;
    for(size_t aa = 0; aa < sizx; ++aa)
    {
        x1[aa] = x[aa] - x0;
        y1[aa] = y[aa] - x0;
        if(aa != sizx-1)
        {
            A = A + (x1[aa]*y1[aa+1] - x1[aa+1]*y1[aa]);
            B = B + ((x1[aa]+x1[aa+1])*(x1[aa]*y1[aa-1]-x1[aa-1]*y1[aa]));
        }
        else if(aa == sizx-1)
        {
            A = A + (x1[aa] - y1[aa]);
            B = B + ((x1[aa]+1)*(x1[aa]*1-1*y1[aa]));
        }
    }
    A = A*0.5;
    C[0] = ID;
    C[1] = ((1/6/A)*B)+x0;
    C[2] = ((1/6/A)*B)+y0;
    return C;
}

template <typename T>

void PrintValues(const std::string& title, std::vector<std::vector<T>>& v, std::ofstream outfil)
{
    if(outfil.is_open())
    {
        outfil << "ID,X,Y,Z \n";
        std::cout << title << std::endl;
        for(size_t line = 0; line < v.size(); ++line)
        {
            for(size_t val = 0; val < v[line].size(); ++val)
            {
                std::cout << v[line][val] << " ";
                outfil << v[line][val] << ",";
            }
            outfil << "\n";
            std::cout << std::endl;
        }
        std::cout << std::endl;
    }
}

int main(int argc, char* argv[])
{

    std::ofstream & outfil;

    if (argc < 2)
    {
        std::cerr << argv[0] << " needs to get input file (2dm)" << std::endl;
    }

    else if (argc == 3)
    {
        outfil.open(argv[2]);
    }

    else
    {
        outfil.open(std::string(argv[1]) + ".csv");
    }

    std::vector<std::vector<std::string>> values;
    std::ifstream fin(argv[1]);

    for (std::string line; std::getline(fin, line); )
    {
        std::istringstream in(line);
        values.push_back(
                         std::vector<std::string>(std::istream_iterator<std::string>(in),
                                                  std::istream_iterator<std::string>()));
    }

    std::vector<std::vector<int>> cells;
    std::vector<std::vector<double>> nodes;

    for (size_t i = 0; i < values.size(); ++i)
    {
        if(values[i][0] == "E3T")
        {
            cells.push_back(GetValues_c(values[i], 1, 5));
        }
        else if(values[i][0] == "E4Q")
        {
            cells.push_back(GetValues_c(values[i], 1, 6));
        }
        else if(values[i][0] == "ND")
        {
            nodes.push_back(GetValues_n(values[i], 1, 4));
        }
    }

    std::vector<std::vector<double>> cell_centres;

    for (size_t aa = 0; aa < cells.size(); ++aa)
    {
        if(cells[aa].size() == 5)
        {
            std::vector<double> xs;
            xs.at(0) = nodes[cells[aa][1] - 1][1];
            xs.at(1) = nodes[cells[aa][2] - 1][1];
            xs.at(2) = nodes[cells[aa][3] - 1][1];
            std::vector<double> ys;
            ys.at(0) = nodes[cells[aa][1] - 1][2];
            ys.at(1) = nodes[cells[aa][2] - 1][2];
            ys.at(2) = nodes[cells[aa][3] - 1][2];
            cell_centres.push_back(polycentre(xs,ys,aa+1));
        }
        else if(cells[aa].size() == 6)
        {
            std::vector<double> xs;
            xs.at(0) = nodes[cells[aa][1] - 1][1];
            xs.at(1) = nodes[cells[aa][2] - 1][1];
            xs.at(2) = nodes[cells[aa][3] - 1][1];
            xs.at(3) = nodes[cells[aa][4] - 1][1];
            std::vector<double> ys;
            ys.at(0) = nodes[cells[aa][1] - 1][2];
            ys.at(1) = nodes[cells[aa][2] - 1][2];
            ys.at(2) = nodes[cells[aa][3] - 1][2];
            ys.at(3) = nodes[cells[aa][4] - 1][2];
            cell_centres.push_back(polycentre(xs,ys,aa+1));
        }
    }

    PrintValues("Cell Centres", cell_centres, outfil);
    //PrintValues("Cells", cells, outfil);
    //PrintValues("Nodes", nodes, outfil);

    return 0;
}

和错误是：

1>------ Build started: Project: cell_centres_v2, Configuration: Debug Win32 ------
1>  main.cpp
1>c:\users\********\documents\visual studio 2010\projects\cell_centres_v2\cell_centres_v2\main.cpp(43): warning C4018: '<' : signed/unsigned mismatch
1>c:\program files (x86)\microsoft visual studio 10.0\vc\include\fstream(1116): error C2248: 'std::basic_ios<_Elem,_Traits>::basic_ios' : cannot access private member declared in class 'std::basic_ios<_Elem,_Traits>'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          c:\program files (x86)\microsoft visual studio 10.0\vc\include\ios(176) : see declaration of 'std::basic_ios<_Elem,_Traits>::basic_ios'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
1>          This diagnostic occurred in the compiler generated function 'std::basic_ofstream<_Elem,_Traits>::basic_ofstream(const std::basic_ofstream<_Elem,_Traits> &)'
1>          with
1>          [
1>              _Elem=char,
1>              _Traits=std::char_traits<char>
1>          ]
========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

非常感谢。

推荐答案

无效函数printValues​​（常量的std :: string的＆放大器;标题的std ::矢量＆lt;的std ::矢量＆lt; T＆GT;＆GT;＆安培;五，性病::的ofstream outfil）通过值的需要的std ::的ofstream 的，也就是复制实际你传递给它的参数，但 fstreams 的可能的不可以被复制，因此错误看到有关它的私有基地。

void PrintValues(const std::string& title, std::vector<std::vector<T>>& v, std::ofstream outfil) takes a std::ofstream by value, that is, copying the actual argument you pass to it, but fstreams may not be copied, hence the error you get regarding the private base it has.

您这样做是正确的时候，你认为是一个解决方案的参考，但你忽略了一点，你应该使用它。为您解决问题的正确方法是参照采取的std ::的ofstream 的在函数printValues​​ 的C>，要做到这一点，只是其声明更改为以下

You got it right when you thought of references as a solution, but you missed the point where you should use it. The correct way to solve your problem is to take a std::ofstream by reference in PrintValues, to do that, simply change its declaration to the following

Your guess is correct, `void PrintValues(const std::string& title, std::vector<std::vector<T>>& v, std::ofstream& outfil)

这篇关于C ++编译器错误不能访问类中声明私有成员'的std :: basic_ios＆LT; _Elem，_Traits＆GT;'的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！