使用std::tie比较结构

Question

我在我的Qt C++应用程序中有这段代码。我用于比较结构的operator==总是返回false，即使它们是相等的。我的代码出了什么问题？

下面是一个有问题的代码片段：

struct pSettings
{
    int speciality;
    bool autoCompleteByWord;
    bool showChronicConditions;
    bool showNavArrows;
    bool smallScreenMode;
    bool simpleExamination;
    bool alwaysSave;
    bool inLinePatientList;
    double newVisitPrice;
    double followVisitprice1;
    double followVisitprice2;
    double followVisitprice3;
    double followVisitprice4;
    int autosaveinterval;
    bool  autoSave ;
    bool minimizeToTray;
    int selectedTheme;
    QString textColor;
    QString topBGColor;
    QString bottomBGColor;
    QString altWinColor;
    QString buttonColor;
    QString altButtonColor;
    QString textBGColor;
    QString borderColor1;
    QString borderColor2;
    QString altButtonColorHover;
    QString buttonColorHover;
    QString buttonColorDisabled;
    QString buttonBorderColorHover;
    QString comboBGcolor;
    QString buttonTextColor;
    QString comboTextColor;
    double lOffSet,tOffSet;

    QString defaultFont;
    double defaultFontSize;
    bool defaultFontBold;

    QString textboxFont;
    double textboxFontSize;
    bool textboxFontBold;

    int maxFollowUps;
    bool autoClosePrintDlg;
    int maxFollowUpsPerProblem;
    bool autoSetnewAfterMaxPerProblemIsReached;
    int checkoutDate;
    int checkoutTime;
    bool enableVisualEffects;

    bool operator==(const pSettings& psettings) const
    {
        return std::tie(
                    speciality,
                    autoCompleteByWord,
                    showChronicConditions,
                    showNavArrows,
                    smallScreenMode,
                    simpleExamination,
                    alwaysSave,
                    inLinePatientList,
                    newVisitPrice,
                    followVisitprice1,
                    followVisitprice2,
                    followVisitprice3,
                    followVisitprice4,
                    autosaveinterval,
                    autoSave ,
                    minimizeToTray,
                    selectedTheme,
                    textColor,
                    topBGColor,
                    bottomBGColor,
                    altWinColor,
                    buttonColor,
                    altButtonColor,
                    textBGColor,
                    borderColor1,
                    borderColor2,
                    altButtonColorHover,
                    buttonColorHover,
                    buttonColorDisabled,
                    buttonBorderColorHover,
                    comboBGcolor,
                    buttonTextColor,
                    comboTextColor,
                    lOffSet,
                    tOffSet,
                    defaultFont,
                    defaultFontSize,
                    defaultFontBold,
                    textboxFont,
                    textboxFontSize,
                    textboxFontBold,
                    maxFollowUps,
                    autoClosePrintDlg,
                    maxFollowUpsPerProblem,
                    autoSetnewAfterMaxPerProblemIsReached,
                    checkoutDate,
                    checkoutTime,
                    enableVisualEffects) ==
                std::tie(psettings.speciality,
                         psettings.autoCompleteByWord,
                         psettings.showChronicConditions,
                         psettings.showNavArrows,
                         psettings.smallScreenMode,
                         psettings.simpleExamination,
                         psettings.alwaysSave,
                         psettings.inLinePatientList,
                         psettings.newVisitPrice,
                         psettings.followVisitprice1,
                         psettings.followVisitprice2,
                         psettings.followVisitprice3,
                         psettings.followVisitprice4,
                         psettings.autosaveinterval,
                         psettings.autoSave ,
                         psettings.minimizeToTray,
                         psettings.selectedTheme,
                         psettings.textColor,
                         psettings.topBGColor,
                         psettings.bottomBGColor,
                         psettings.altWinColor,
                         psettings.buttonColor,
                         psettings.altButtonColor,
                         psettings.textBGColor,
                         psettings.borderColor1,
                         psettings.borderColor2,
                         psettings.altButtonColorHover,
                         psettings.buttonColorHover,
                         psettings.buttonColorDisabled,
                         psettings.buttonBorderColorHover,
                         psettings.comboBGcolor,
                         psettings.buttonTextColor,
                         psettings.comboTextColor,
                         psettings.lOffSet,
                         psettings.tOffSet,
                         psettings.defaultFont,
                         psettings.defaultFontSize,
                         psettings.defaultFontBold,
                         psettings.textboxFont,
                         psettings.textboxFontSize,
                         psettings.textboxFontBold,
                         psettings.maxFollowUps,
                         psettings.autoClosePrintDlg,
                         psettings.maxFollowUpsPerProblem,
                         psettings.autoSetnewAfterMaxPerProblemIsReached,
                         psettings.checkoutDate,
                         psettings.checkoutTime,
                         psettings.enableVisualEffects);
    }

};

Answer 1

在teo长列表中的某处，您会发现它们不完全相同的错误。你违反了DRY (不要重复)。

在C++14中：

auto mytie() const {
  return std::tie( /* ... fields */ );
}

然后使用它来编写==。

在C++11中，您必须将mytie(blah const& self)作为本地(无状态) lambda来编写，以保持合理。

如果这失败了，那么它们会比较不相等，因为它们的不同之处是你没有注意到的。

Answer 2

为此，您可以使用高阶宏函数：

#define ITEMS                   \
ITEM(int,  speciality)          \
ITEM(bool, autoCompleteByWord)  \
...
ITEM(int,  checkoutTime)        \
LAST(bool, enableVisualEffects)

#define ITEM(x,y) x y;
#define LAST(x,y) ITEM(x,y)

struct pSettings
{
    ITEMS
}

#define ITEM(x,y) y,
#define LAST(x,y) y

auto mytie() const
{
    return std::tie
    (
        ITEMS
    );
}

最好在单独的文件中编写项定义