c++ - Qt: undefined reference

刚开始使用Qt并遇到错误，想知道是否有人可以阐明该问题。谷歌搜索并研究了类似的问题，但似乎无法解决。

C:\Users\Seb\Desktop\SDIcw2\main.cpp:10: error: undefined reference to `SDI::shipHandler::shipHandler(SDI::shipHandler&)'

出现在第10行，“ w.populateCombo（shipHandler）;”。在我的main.cpp中；

#include "widget.h"
#include <QApplication>
#include "shipHandler.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    Widget w;
    w.show();
    SDI::shipHandler shipHandler("ships/ships.txt");
    w.populateCombo(shipHandler);
    return a.exec();
}

shipHandler.cpp（构造函数和析构函数）

SDI::shipHandler::shipHandler(std::string fileName)
{
    shipCount = 0;
    std::string line;
    std::ifstream infile;
    infile.open(fileName.c_str());
    while(!infile.eof())
    {
        getline(infile,line);
        shipHandler::lineParse(line);
        shipCount++;
    }
    infile.close();
}

SDI::shipHandler::~shipHandler()
{
}

shipHandler.h

#ifndef SDI__shipHandler
#define SDI__shipHandler
#include "common.h"
#include "navalVessels.h"

namespace SDI
{
    class shipHandler
    {
        //variables
    public:
        std::vector<SDI::navalVessels*> ships;
        int shipCount;
    private:

        //function
    public:
        shipHandler();
        shipHandler(std::string fileName);
        shipHandler(SDI::shipHandler& tbhCopied);
        ~shipHandler();

        void lineParse(std::string str);
        void construct(std::vector<std::string> line);
        std::vector<int> returnDates(std::string dates);
    private:
    };
}

#endif

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最佳答案

只是阅读错误消息，看起来它正在尝试使用复制构造函数（shipHandler(SDI::shipHandler& tbhCopied)），但是您从未在shipHandler.cpp中完全定义它。

class shipHandler
{
    // ...
public:
    shipHandler(); // this isn't defined anywhere
    shipHandler(std::string fileName);
    shipHandler(SDI::shipHandler& tbhCopied); // this isn't defined anywhere
    ~shipHandler();

    // ...
};

首先，您应该停止声明副本构造函数，或者完成对它的定义：

// in shipHandler.cpp
SDI::shipHandler::shipHandler(SDI::shipHandler& tbhCopied) {
    // fill this in
}

您还应该定义或删除默认构造函数（SDI::shipHandler::shipHandler()）。

接下来，您可以传递shipHandler作为参考，而不用创建副本：

// most likely, this is what you want
void Widget::populateCombo(const shipHandler& handler);

// or maybe this
void Widget::populateCombo(shipHandler& handler);

这些可能是有用的参考：

What is the difference between a definition and a declaration?

c++ passing arguments by reference and pointer