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我一直在搞乱 Qt 和 C++ 一段时间，但我遇到了这个错误，似乎无法弄清楚它为什么会出现。const void* 转换错误消息已经回答了很多其他问题，但我真的看不出这些解释对我的情况有什么帮助，所以这里是：

我有一个 QList< MyType *const> 的重新实现“MyTypeManager”，因此是指向非 const MyTypes 的 const 指针列表。但是，当我重新实现一个函数时， addMyType 被调用

void MyTypeManager::addMyType(MyType *const var)
{
     this->append(var);
}

发生以下错误：

In file included from /usr/include/qt4/QtCore/QList:1:0,
             from ../qtsdlthread/mytypemanager.h:4,
             from ../qtsdlthread/mytypemanager.cpp:1:
/usr/include/qt4/QtCore/qlist.h: In member function ‘void QList<T>::node_construct(QList<T>::Node*, const T&) [with T = MyType* const]’:
/usr/include/qt4/QtCore/qlist.h:499:13:   instantiated from ‘void QList<T>::append(const T&) [with T = MyType* const]’
../qtsdlthread/mytypemanager.cpp:20:26:   instantiated from here
/usr/include/qt4/QtCore/qlist.h:359:58: error: invalid conversion from ‘const void*’ to ‘void*’
/usr/include/qt4/QtCore/qlist.h: In member function ‘void QList<T>::node_copy(QList<T>::Node*, QList<T>::Node*, QList<T>::Node*) [with T = MyType* const]’:
/usr/include/qt4/QtCore/qlist.h:666:9:   instantiated from ‘QList<T>::Node* QList<T>::detach_helper_grow(int, int) [with T = MyType* const]’
/usr/include/qt4/QtCore/qlist.h:497:48:   instantiated from ‘void QList<T>::append(const T&) [with T = MyType* const]’
../qtsdlthread/mytypemanager.cpp:20:26:   instantiated from here
/usr/include/qt4/QtCore/qlist.h:386:17: error: invalid conversion from ‘const void*’ to ‘void*’

mytypemanager 中的 20:26 是上面发布的 this->append 行。

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1 回答 1

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From the documentation:

QList's value type must be an assignable data type.

Alas MyType *const is not assignable. You have several remedies:

1. Make T a mutable pointer

2. Make T a pointer to your const pointer:

typedef MyType *const Element

void MyTypeManager::addMyType(Element var)
{
    Element* ptr2ptr = new Element(var);
    this->append(ptr2ptr);
}

But now you have 2 levels of memory management to worry about.

3. (Dangerous) Make T=MyType* and const-cast MyType *const into MyType *:

this->append(const_cast<MyType *>(var));

This will only work if you are certain var was originally created as a MyType* variable.

于 2011-09-02T15:10:00.717 回答