访问对象列表中的非常量成员
我想访问此类对象列表中包含的对象的成员。
我有一个类 CApp ，其成员为 std::list 用作粒子列表。
类 Particle 有一个成员 void Update() 根据我对 const 的理解，它不能是 const，因为它会影响实例（欧拉积分等）。
我想迭代 PList 来更新所有粒子。
粒子构造函数包括：
Particle::Particle(std::list<Particle>* PList_In) {
PList = PList_In;
PList->push_back(*this);
}
多次调用以下内容：
Particle(&PList);
因此列表似乎已建立。作为旁注，如果有人能够解释此时内存中实际存在的内容（指针、引用），那就太好了。
但基本上这是错误的：
// Update all particles
std::list<Particle>::const_iterator iter;
for (iter = PList.begin(); iter != PList.end(); iter++) {
iter->Update();
}
不确定
error: passing ‘const Particle’ as ‘this’ argument of ‘void Particle::Update()’ discards qualifiers
如何处理这个，如果需要更多信息/解释，请告诉我。
提前致谢！
I would like to access members of objects contained in a list of such objects.
I have a class CApp with a member std::list<Particle> PList serving as a list of particles.
A class Particle has a member void Update() which from my understanding of const can't be const because it affects the instance (euler integration and stuff).
I would like to iterate through PList to update all of the particles.
A Particle constructor includes:
Particle::Particle(std::list<Particle>* PList_In) {
PList = PList_In;
PList->push_back(*this);
}
The following is called several times:
Particle(&PList);
So the list appears to be set up. As a side note, if anyone could explain what's actually there in terms of memory (pointers, references) at this point that would be great.
But basically this errs:
// Update all particles
std::list<Particle>::const_iterator iter;
for (iter = PList.begin(); iter != PList.end(); iter++) {
iter->Update();
}
with
error: passing ‘const Particle’ as ‘this’ argument of ‘void Particle::Update()’ discards qualifiers
Not sure what to do with this, if more information/explanation is required, let me know.
Thanks in advance!
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通过使用 const_iterator，您表示您不想更改列表元素。
如果需要，请使用 std::list::iterator。
By using const_iterator you say that you don't want to change list elements.
If you want to, use std::list::iterator.
通过使用const_iterator，您将告诉编译器您不会在修改指向对象的方法上使用此迭代器。方法是否修改对象由其 const 限定符决定。例如，如果您在
class A中有一个类似int get() const;的方法声明，那么此方法保证它不会修改class A< 的对象/代码>。在您的情况下，似乎Update没有 const 限定符，因此编译器抱怨您无法使用const_iterator调用非常量函数。您需要更改迭代器类型std::list::iterator 。作为旁注，请考虑通过引用传递
list对象，而不是在函数中使用指针。By using
const_iteratoryou are telling the compiler that you are not going to use this iterator on methods which modify the pointed to objects. Whether a method modifies the object or not is determined by its const qualifier. For example if you have a method declaration likeint get() const;insideclass Athen this method is guaranteeing that it will not modify objects ofclass A. In your case it seemsUpdateis not having the const qualifier hence the compiler is complaining that you can not call a non-const function using aconst_iterator. You need to change the iterator typestd::list<Particle>::iterator.As a side note consider passing the
listobject by reference instead of using the pointer in your function.