blocks|key|1614605|text|你不应该在这里选角。在if-else链中，您要做的是创建一个指向适当类型的共享指针，然后返回该shared_ptr。它将自动转换为std::shared_ptr<Character>，就像您在|type|unstyled|depth|inlineStyleRanges|offset|length|style|CODE|entityRanges|data|1614606|Character+*+character+=+new+Enemy(...);|code-block|syntax|javascript|1614607|这意味着您的函数应该如下所示|1614608|std::shared_ptr<Character>+CharacterFactory::createCharacter(Character::Type+type,+Character::SubType+subtype,+const+TextureHolder+&textures,+sf::Vector2u+windowSize)+{++++
++++if+(+type+==+Character::enemy+)+{
++++++++return+std::make_shared<Enemy>(subType,+textures,+windowSize);
++++}+else+if(type+==+Character::player)+{
++++++++return+std::make_shared<Player>(subType,+textures,+windowSize);
++++}+
++++return+{};+//+return+null+on+bad+type
}|1614609|1614610|我们可以对上面的代码应用几个tweeks，以使其性能更好，而不是在工厂收到错误的type时静默返回空指针。为了做到这一点，我们将使用一个std::unique_ptr，如果我们得到一个坏的type，我们将抛出一个异常。可以将std_unique_ptr转换为std::shared_ptr，因此默认情况下，您的工厂可以同时使用这两种类型的智能指针。这给了我们|1614611|std::unique_ptr<Character>+CharacterFactory::createCharacter(Character::Type+type,+Character::SubType+subtype,+const+TextureHolder+&textures,+sf::Vector2u+windowSize)+{++++
++++if+(+type+==+Character::enemy+)+{
++++++++return+std::make_unique<Enemy>(subType,+textures,+windowSize);
++++}+else+if(type+==+Character::player)+{
++++++++return+std::make_unique<Player>(subType,+textures,+windowSize);
++++}+
++++throw+std::runtime_error("bad+type+passed+to+factory");
}|1614612|entityMap^0|1B|A|1T|Q|0|0|0|0|0|14|4|1W|F|2M|4|34|E|3L|F|0|0^^$0|@$1|2|3|4|5|6|7|V|8|@$9|W|A|X|B|C]|$9|Y|A|Z|B|C]]|D|@]|E|$]]|$1|F|3|G|5|H|7|10|8|@]|D|@]|E|$I|J]]|$1|K|3|L|5|6|7|11|8|@]|D|@]|E|$]]|$1|M|3|N|5|H|7|12|8|@]|D|@]|E|$I|J]]|$1|O|3|-4|5|6|7|13|8|@]|D|@]|E|$]]|$1|P|3|Q|5|6|7|14|8|@$9|15|A|16|B|C]|$9|17|A|18|B|C]|$9|19|A|1A|B|C]|$9|1B|A|1C|B|C]|$9|1D|A|1E|B|C]]|D|@]|E|$]]|$1|R|3|S|5|H|7|1F|8|@]|D|@]|E|$I|J]]|$1|T|3|-4|5|6|7|1G|8|@]|D|@]|E|$]]]|U|$]]

You shouldn't be casting here. In your if-else chain what you do is create a shared pointer to the appropriate type and then return that <code>shared_ptr</code>. It will automatically get converted to a <code>std::shared_ptr&lt;Character&gt;</code> just like you get when you have

<pre><code>Character * character = new Enemy(...);
</code></pre>

That means your function should look something like

<pre><code>std::shared_ptr&lt;Character&gt; CharacterFactory::createCharacter(Character::Type type, Character::SubType subtype, const TextureHolder &amp;textures, sf::Vector2u windowSize) { 
 if ( type == Character::enemy ) {
 return std::make_shared&lt;Enemy&gt;(subType, textures, windowSize);
 } else if(type == Character::player) {
 return std::make_shared&lt;Player&gt;(subType, textures, windowSize);
 } 
 return {}; // return null on bad type
}
</code></pre>

<hr>

We can apply a few tweeks to the above to make it more performant and to not just silently return a null pointer if the factory is passed a bad <code>type</code>. To do that we will use a <code>std::unique_ptr</code> and throw an exception if we get a bad <code>type</code>. <code>std_unique_ptr</code> can be converted to a <code>std::shared_ptr</code> so this lets your factory work with both types of smart pointers by default. That gives us

<pre><code>std::unique_ptr&lt;Character&gt; CharacterFactory::createCharacter(Character::Type type, Character::SubType subtype, const TextureHolder &amp;textures, sf::Vector2u windowSize) { 
 if ( type == Character::enemy ) {
 return std::make_unique&lt;Enemy&gt;(subType, textures, windowSize);
 } else if(type == Character::player) {
 return std::make_unique&lt;Player&gt;(subType, textures, windowSize);
 } 
 throw std::runtime_error("bad type passed to factory");
}
</code></pre>

I'm trying to implement a factory of characters but I can't understand how to create a generic shared_ptr to the virtual base class and then cast it to a derived class with arguments in the constructor. 
In my example, my virtual base class can't take arguments in the constructor, but I need them in the constructor of the derived class.

<pre><code>std::shared_ptr&lt;Character&gt; CharacterFactory::createCharacter(Character::Type type, Character::SubType subtype, const TextureHolder &amp;textures, sf::Vector2u windowSize) {

 std::shared_ptr&lt;Character&gt; character;

 if ( type == Character::enemy ) {
 std::dynamic_pointer_cast&lt;Enemy&gt;(character)(subType, textures, windowSize);

 } else if(type == Character::player) {
 //cast to player ...
 }

 return character;
</code></pre>

Probably it's a design problem and I can't solve it. I can't use raw pointers, if I could I think that

<pre><code>character = new Enemy(...);
</code></pre>

would have worked. All examples I have found for casting use default constructors.

Thank you for your help

call constructor of a derived class after a dynamic_pointer_cast

翻译质量差，导致语言生硬或混乱。

没有提供实际的解决方法或示例。

解答不清晰，无法理解或解决问题。

页面排版不美观，阅读体验差。

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我正在尝试实现一个字符工厂，但是我不能理解如何为虚拟基类创建一个泛型shared_ptr，然后将它转换为一个在构造函数中带有参数的派生类。在我的示例中，我的虚拟基类不能在构造函数中接受参数，但我需要在派生类的构造函数中使用它们。std::shared_ptr<Character> CharacterFactory::c...

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