From 4faf011c3f5f4a739f4ddc54040b5319f7fe5d90 Mon Sep 17 00:00:00 2001 From: Ulf Hermann Date: Thu, 10 Jan 2019 17:38:55 +0100 Subject: [PATCH] Document that you shouldn't Q_ENUM() things outside the int range The meta object system stores enums as signed int, probably for performance reasons. This is good enough for about 99% of the use cases. If you try to register larger types and then access them through the metaobject system, you can get undefined behavior. Task-number: QTBUG-71947 Change-Id: I16b395547c22fad10b476c2c2a0768538db0a20e Reviewed-by: Thiago Macieira --- src/corelib/kernel/qobject.cpp | 12 ++++++++++++ 1 file changed, 12 insertions(+) diff --git a/src/corelib/kernel/qobject.cpp b/src/corelib/kernel/qobject.cpp index 4680742a3e..42c39f18e3 100644 --- a/src/corelib/kernel/qobject.cpp +++ b/src/corelib/kernel/qobject.cpp @@ -4338,6 +4338,12 @@ QDebug operator<<(QDebug dbg, const QObject *o) in a QVariant, you can convert them to strings. Likewise, passing them to QDebug will print out their names. + Mind that the enum values are stored as signed \c int in the meta object system. + Registering enumerations with values outside the range of values valid for \c int + will lead to overflows and potentially undefined behavior when accessing them through + the meta object system. QML, for example, does access registered enumerations through + the meta object system. + \sa {Qt's Property System} */ @@ -4389,6 +4395,12 @@ QDebug operator<<(QDebug dbg, const QObject *o) used in a QVariant, you can convert them to strings. Likewise, passing them to QDebug will print out their names. + Mind that the enum values are stored as signed \c int in the meta object system. + Registering enumerations with values outside the range of values valid for \c int + will lead to overflows and potentially undefined behavior when accessing them through + the meta object system. QML, for example, does access registered enumerations through + the meta object system. + \sa {Qt's Property System} */