如何在包含指向元素的指针的集合中找到一个元素? [英] How can I find an element in a set which contains pointers to the elements?

问题描述

:我更正了一个错误:我使用的是set而不是vector.

I fixed my mistake: I'm using a set and not a vector.

请考虑以下示例代码:

set<Foo *> set_of_foos;

set_of_foos.insert(new Foo(new Bar("x")));
set_of_foos.insert(new Foo(new Bar("y")));
[...]

// The way a "foo" is found is not important for the example.
bool find_foo(Foo *foo) {
  return set_of_foos.end() != set_of_foos.find(foo);
}

现在我打电话给

find_foo(new Foo(new Bar("x")));

该函数返回false，因为找不到我要查找的内容.对我来说，原因很明显:指针指向不同的对象，因为它们都被分配了new，从而导致地址的值不同.

the function returns false since what I'm looking for can't be found. The reason is obvious to me: The pointers point to different objects since they are allocated both with a new, resulting in different values of the addresses.

但是我想比较Foo的内容(即上例中的"x")而不是Foo *本身.除了修改Foo之外，不能使用Boost.

But I want to compare the contents of Foo (i.e. "x" in the above example) and not Foo * itself. Using Boost is not an option as well as modifying Foo.

我是否需要遍历set_of_foos内部的每个Foo *，还是有一个更简单的解决方案?我尝试对每个Foo的内容进行唯一的序列化，然后将set<Foo *>替换为map<string, Foo *>，但这似乎是一个非常"hacked"的解决方案，效率不高.

Do I need to loop through each of the Foo * inside set_of_foos or is there a simpler solution? I tried uniquely serializing the contents of each Foo and replace the set<Foo *> with a map<string, Foo *>, but this seems like a very "hacked" solution and not very efficient.

推荐答案

find_foo(new Foo(new Bar("x")));听起来不是个好主意-在任何情况下，该搜索功能很可能导致内存泄漏.

find_foo(new Foo(new Bar("x"))); does not sound like a good idea - it will most likely (in any scenario) lead to memory leak with that search function.

您可以将find_if与函子一起使用:

You could use find_if with a functor:

struct comparator {
    Foo* local;
    comparator(Foo* local_): local(local_) {}
    ~comparator() { /* do delete if needed */ } 
    bool operator()(const Foo* other) { /* compare local with other */ }
};

bool found = vec.end() != std::find_if(vec.begin(), vec.end(), comparator(new Foo(...)));

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