C++/Win32 构造函数未使用从对话框获取的字符串初始化变量

Question

我正在尝试创建一个 object 和从对话框中获取的 std::string，在调试时我看到它已成功获取并传递给构造函数，但是本地参数保持为“”。

这是我的 class header:

#pragma once
#include <iostream>
#include <istream>
#include <fstream>
#include <string>

class Motorcycle
{
public:
    Motorcycle();
    Motorcycle(const std::string& nameP, int mileage) : name(nameP), mileage(mileage) {};

    friend std::ostream & operator << (std::ostream & out, const Motorcycle & obj)
    {
        out << obj.name << "\n" << obj.mileage << std::endl;
        return out;
    };

    //friend std::istream & operator >> (std::istream & in, const Motorcycle & obj)
    //{
    //  in >> &obj.name[0] >> obj.mileage;
    //  return in;
    //};

private:
    std::string name;
    int mileage;
};

cpp 仍然是空的（我想也许我应该把构造函数放在那里，但结果还是一样？）：

#include "stdafx.h"
#include "Motorcycle.h"
#include <string>

Motorcycle::Motorcycle()
{
}

//Motorcycle::Motorcycle(const std::string &nameP, int mileage) : name(nameP), mileage(mileage) {};

这是对话框和其他函数的过程：

    BOOL CALLBACK CreateBikeProc(HWND hWnd, UINT message, WPARAM wParam, LPARAM lParam)
{
    std::string name = "";
    int mileage;

    switch (message)
    {
    case WM_INITDIALOG:

        return TRUE;
    case WM_COMMAND:
        switch (LOWORD(wParam))
        {
        case IDOK:
            GetDlgItemTextA(hWnd, IDC_EDIT_NAME, &name[0], 16);
            mileage = GetDlgItemInt(hWnd, IDC_EDIT_MILEAGE, NULL, FALSE);
            if (ValidateBike(name, mileage))
            {
                CreateBike(name, mileage);
                EndDialog(hWnd, IDOK);
            }
            break;
        case IDCANCEL:
            EndDialog(hWnd, IDCANCEL);
            break;
        }
        break;
    default:
        return FALSE;
    }
    return TRUE;
}

BOOL ValidateBike(std::string& name, int mileage)
{
    if (name[0] == ' ' || name.find_first_not_of(' ') != name.npos
        || mileage < 1)
        return false;
    
    return true; 
}
BOOL CreateBike(std::string& name, int mileage)
{

    Motorcycle bike = Motorcycle(name, mileage);
    
    std::ofstream ofs("motorcycles.txt", std::ios::app);
    ofs << bike;
    ofs.close();

    return true;
}

我可以看到 CreateBikeProc 中的名称已分配并传递给其他函数，但是 bike.name 是空的...

此外，friend std::istream & operator >> 被注释掉了，因为它会导致另一个错误... Error 1 error C2678: binary '>>' : no operator found which takes a left-hand operand of type 'std::istream' (or there is no acceptable conversion)

提前致谢...

Answer 1

问题出在这里：

GetDlgItemTextA(hWnd, IDC_EDIT_NAME, &name[0], 16);

您不能像这样将值读入字符串。您需要创建一个缓冲区，然后从缓冲区更新字符串：

char buffer[17]="";
GetDlgItemTextA(hWnd, IDC_EDIT_NAME, &buffer, 16);
name=buffer;

对于 operator>>，您有两个问题：第一个是 const Motorcycle 参数，第二个是您试图就地覆盖字符串。这是固定版本：

    friend std::istream & operator >> (std::istream & in, Motorcycle & obj)
    {
      in >> obj.name >> obj.mileage;
      return in;
    };

C++/Win32 构造函数未使用从对话框获取的字符串初始化变量

C++/Win32 constructor not initializing variable with string obtained from dialog

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