CODEWITHSUNDEEP
c++qt
Carlton
Carlton

Reputation: 4297

Broken bitwise-or operator in a Qt project

I just recently added a QLabel to a ui form in a Qt project, set its text alignment to a custom value, and was then surprised to find that the auto-generated code for the ui class caused a compiler error in MSVC:

ui_projectwidget.h:109:
error: C2664: 'void QLabel::setAlignment(Qt::Alignment)' : cannot convert argument 1 from 'int' to 'Qt::Alignment'

Qt::Alignment is a flag to indicate left/right/center/etc. text justification. The offending line in ui_projectwidget.h is:

componentName->setAlignment(Qt::AlignLeading|Qt::AlignLeft|Qt::AlignTop);

In this project, I overload operator | for a scoped enum, MIBC::ItemType, that is unrelated to Qt components:

using FlagType = int64_t;
enum class ItemType: FlagType {
      type1, type2, etc
}

using Ty = std::underlying_type_t<MIBC::ItemType>;

inline MIBC::ItemType operator| (MIBC::ItemType lhs, MIBC::ItemType rhs) {
    return static_cast<MIBC::ItemType>(static_cast<Ty>(lhs) | static_cast<Ty>(rhs));
}

I was able to fix the compiler error by adding another overload for operator | for Qt::AlignmentFlag:

inline Qt::AlignmentFlag operator|(Qt::AlignmentFlag lhs, Qt::AlignmentFlag rhs) {
    return static_cast<Qt::AlignmentFlag>(static_cast<int>(lhs) | static_cast<int>(rhs));
}

Even though I've "fixed" the problem, I still don't understand it. What broke the default operator | such that it no longer accepts Qt::AlignmentFlag? Should I restructure my scoped enum in some way that it doesn't interfere with other bitwise-or operators?

Upvotes: 1

Views: 638

Answers (1)

Kuba hasn&#39;t forgotten Monica
Kuba hasn&#39;t forgotten Monica

Reputation: 98485

Most likely, you declared the operator in the global namespace, breaking the argument dependent lookup. Instead, you should have put it in the namespace of its arguments, and let ADL pick it up.

Upvotes: 1

Related Questions