C++ remove_if 在对象向量上
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C++ remove_if on a vector of objects
提问by Jordan
I have a vector (order is important) of objects (lets call them myobj class) where I'm trying to delete multiple objects at a time.
我有一个对象的向量（顺序很重要）（让我们称它们为 myobj 类），我试图一次删除多个对象。
class vectorList
{
vector<*myobj> myList;
};
class myobj
{
char* myName;
int index;
bool m_bMarkedDelete;
}
I was thinking that the best way to do this would be to mark specific myobj objects for deletion and then call myList.remove_if() on the vector. However, I'm not exactly sure how to use predicates and such for this. Should I create a member variable in the object which allows me to say that I want to delete the myobj and then create a predicate which checks to see if the member variable was set?
我认为最好的方法是将特定的 myobj 对象标记为删除，然后在向量上调用 myList.remove_if() 。但是，我不确定如何为此使用谓词等。我应该在对象中创建一个成员变量，它允许我说我想删除 myobj 然后创建一个谓词来检查是否设置了成员变量？
How do I implement the predicate as a part of the vectorList class?
如何将谓词实现为 vectorList 类的一部分？
回答by Benjamin Lindley
Should I create a member variable in the object which allows me to say that I want to delete the myobj and then create a predicate which checks to see if the member variable was set?
我应该在对象中创建一个成员变量，它允许我说我想删除 myobj 然后创建一个谓词来检查是否设置了成员变量？
Haven't you already done that? Isn't that what m_bMarkedDeleteis for? You would write the predicate like this:
你不是已经这样做了吗？不m_bMarkedDelete就是为了这个吗？你可以这样写谓词：
bool IsMarkedToDelete(const myobj & o)
{
return o.m_bMarkedDelete;
}
Then:
然后：
myList.erase(
std::remove_if(myList.begin(), myList.end(), IsMarkedToDelete),
myList.end());
Or, using lambdas:
或者，使用 lambda 表达式：
myList.erase(
std::remove_if(myList.begin(), myList.end(),
[](const myobj & o) { return o.m_bMarkedDelete; }),
myList.end());
If your class doesn't actually have that member, and you're asking us if it should, then I would say no. What criteria did you use to decide to mark it for deletion? Use that same criteria in your predicate, for example:
如果你的班级实际上没有那个成员，而你问我们是否应该，那么我会说不。您使用什么标准来决定将其标记为删除？在谓词中使用相同的条件，例如：
bool IndexGreaterThanTen(const myobj & o)
{
return o.index > 10;
}
note-- The functions I've written are of course invalid since all your members are private. So you'll need some way to access them.
注意——我写的函数当然是无效的，因为你所有的成员都是私有的。因此，您需要某种方式来访问它们。
回答by AJG85
A predicate is basically a conditional comparison. It can be a function or object. Here's an example using new C++ lambdas. This code will go through the vector and remove the values equal to 3.
谓词基本上是条件比较。它可以是一个函数或对象。这是一个使用新 C++ lambda 的示例。此代码将遍历向量并删除等于 3 的值。
int arg[6] = {1, 2, 3, 3, 3, 5};
std::vector<int> vec(arg, arg+6);
vec.erase(
std::remove_if(
vec.begin(), vec.end(),
[](int i){ return i == 3;}),
vec.end());
Edit:For pointers let's say you had a vector or interfaces you could set them to nullptrthen remove them in a batch with pretty much the same code. In VS2008 you won't have lambdas so make a comparison predicate function or struct instead.
编辑：对于指针，假设您有一个向量或接口，您可以将它们设置为nullptr然后使用几乎相同的代码批量删除它们。在 VS2008 中，您将没有 lambda，因此请改用比较谓词函数或结构。
bool ShouldDelete(IAbstractBase* i)
{
return i == nullptr;
// you can put whatever you want here like:
// return i->m_bMarkedDelete;
}
std::vector<IAbstractBase*> vec;
vec.erase(
std::remove_if(
vec.begin(), vec.end(),
ShouldDelete),
vec.end());
