C++ reinterpret_cast 抛弃限定词
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reinterpret_cast casts away qualifiers
提问by Seb
I add an issue on reinterpreting a variable and I don't know why..
我添加了一个关于重新解释变量的问题，但我不知道为什么..
int ProgressBar(const uint64_t data_sent, const uint64_t data_total, void const * const data) {
Dialog *dialog = reinterpret_cast<Dialog *>(data);
dialog->setValue((data_sent * 100) / data_total);
}
the reinterpret_castseems not allowed and say
在reinterpret_cast似乎不允许，说
reinterpret_cast from 'const void *) to Dialog * casts away qualifiers
reinterpret_cast 从 'const void *) 到 Dialog * 抛弃限定符
Any idea
任何的想法
回答by Pranit Kothari
As Nick Strupat stated in comment,
正如 Nick Strupat 在评论中所说，
reinterpret_cast can't cast away cv-qualifiers
reinterpret_cast 不能抛弃 cv 限定符
So you can use reinterpret_castand const_casttogether.
所以你可以reinterpret_cast和const_cast一起使用。
Dialog *dialog = const_cast<Dialog*>(reinterpret_cast<const Dialog *>(data));
回答by M.M
You need to also use a const_castto remove constqualifiers. Also, casting from void *can use static_cast, it does not need to reinterpret. For example:
您还需要使用 aconst_cast来删除const限定符。此外，从void *可以使用的铸造static_cast，它不需要重新解释。例如：
Dialog const *dialog = static_cast<Dialog const *>(data);
Dialog *d2 = const_cast<Dialog *>(dialog);
However , make sure that the Dialog is actually not a constobject; attempting to modify a const object (presumably setValuedoes this) causes undefined behaviour.
但是，请确保 Dialog 实际上不是const对象；尝试修改 const 对象（大概setValue是这样做的）会导致未定义的行为。
I'd suggest rethinking the interface to ProgressBarto avoid needing this cast.
我建议重新考虑界面ProgressBar以避免需要此演员表。
