作为对象的类成员 - 指针与否？ C ++ [英] Class members that are objects - Pointers or not? C++

问题描述

如果我创建一个类MyClass，它有一些私人成员说MyOtherClass，是更好的让MyOtherClass一个指针或不是？它是什么意思，还有它不是一个指针在它在内存中的存储方面？

我注意到，QT中的例子通常在类是类时将类成员声明为指针。

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如果我创建了一个类MyClass，并且它有一个私人成员说MyOtherClass，是不是更好地让MyOtherClass成为一个指针？

你通常应该声明它作为类中的值。它将是本地的，将有更少的机会错误，较少的分配 - 最终减少可能出错的事情，编译器可以始终知道它是在一个指定的偏移量...它帮助优化和二进制减少在几个级别。将会有一些情况下，你知道你必须处理指针（即多态，共享，需要重新分配），通常最好是只在必要时使用指针 - 特别是当它是私有/封装。

它是什么意思，还有它不是一个指针在存储在内存中的位置？

其地址将接近（或等于）此 - gcc（例如）有一些高级选项转储类数据（大小，vtable，偏移量）

创建类时是否创建对象？

是 - 如果编译器重新对齐，MyClass的大小将增加sizeof（MyOtherClass），或者更多（例如对其自然对齐）

If I create a class MyClass and it has some private member say MyOtherClass, is it better to make MyOtherClass a pointer or not? What does it mean also to have it as not a pointer in terms of where it is stored in memory? Will the object be created when the class is created?

I noticed that the examples in QT usually declare class members as pointers when they are classes.

Regards

Mark

解决方案

If I create a class MyClass and it has some private member say MyOtherClass, is it better to make MyOtherClass a pointer or not?

you should generally declare it as a value in your class. it will be local, there will be less chance for errors, fewer allocations -- ultimately fewer things that could go wrong, and the compiler can always know it is there at a specified offset so... it helps optimization and binary reduction at a few levels. there will be a few cases where you know you'll have to deal with pointer (i.e. polymorphic, shared, requires reallocation), it is typically best to use a pointer only when necessary - especially when it is private/encapsulated.

What does it mean also to have it as not a pointer in terms of where it is stored in memory?

its address will be close to (or equal to) this -- gcc (for example) has some advanced options to dump class data (sizes, vtables, offsets)

Will the object be created when the class is created?

yes - the size of MyClass will grow by sizeof(MyOtherClass), or more if the compiler realigns it (e.g. to its natural alignment)

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