c++ - Qt: undefined reference

Question

刚开始使用 Qt 遇到一个错误，想知道是否有人可以阐明这个问题。用谷歌搜索并查看了类似的问题，但似乎无法找到解决方案；

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()
{
}

船处理程序.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

感谢任何帮助

Answer 1

只是阅读错误消息，它看起来像是在尝试使用复制构造函数 (shippHandler(SDI::shiphandler& tbhCopied))，但您从未在 shippHandler.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，您应该停止声明复制构造函数，或者完成定义它:

// 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，您可以将您的 shipHandler 作为引用传递，而不是创建拷贝:

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

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

这些可能是有用的引用:

What is the difference between a definition and a declaration?

c++ passing arguments by reference and pointer