集合查找中的精确比较
我有一个结构（例如 Foo），其中包含简单的字符串和一个双精度值，并且我创建了一个集合，其中还有一个比较器类，用于比较这些属性的子集。所以我的声明如下： std::set
当我调用 find() 时，我会期望 Foo 的所有属性用作键还是使用 FooComp ？我假设是前者。
我问的原因是我遇到了一个问题，即使我尝试使用 find() 来检查它的存在，但在集合中未检测到之前添加的对象。我只能假设这已经发生了，因为双倍可能存在细微的差异？ double 属性未在比较器中使用，但可能构成键的一部分。
任何想法将不胜感激。
I've got a struct (say Foo) which contains simply strings and a double and I've created a set which also has a comparator class which compares a subset of those attributes. So my Declaration looks like: std::set<Foo, FooComp>
When I call find() would I expect all the attributes of Foo to be used as a key or would FooComp be used? I'm assuming the former.
The reason that I'm asking is that I've got an issue where an object which has been previously added is not detected in the set even though I've tried using find() to check it's presence. I can only assume that this has happened as there was a subtle difference in the double perhaps? The double attribute is not used in the comparitor but presumably forms part of the key.
Any thoughts would be much appreciated.
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FooComp 需要表示一个二元函数，该函数接受 Foo 的 2 个引用，并确定左边的引用在逻辑上是否小于右边的引用。
并以“严格排序”实现operator()，因此
!FooComp( foo1, foo1 )FooComp( foo1, foo2 )=>!FooComp( foo2, foo1 )FooComp( foo1, foo2 )&&FooComp( foo2, foo3 )=>;FooComp( foo1, foo3 )实际上第一个公理可以从第二个公理推导出来，所以你只需要第二个和第三个公理。
FooComp needs to represent a binary function that takes 2 references to Foo and determines if the left one is logically less than the right one.
and implement operator() with "strict ordering" thus
!FooComp( foo1, foo1 )FooComp( foo1, foo2 )=>!FooComp( foo2, foo1 )FooComp( foo1, foo2 )&&FooComp( foo2, foo3 )=>FooComp( foo1, foo3 )Actually the first axiom can be deduced from the second so you only need the 2nd and 3rd axioms.
std::set::find()将使用FooComp，只要 double 不构成该比较的一部分，就应该没问题。std::find需要operator==，因此再次取决于您是否定义了它以及它包含的内容，只要它不包含 double （或包含以合理的方式加倍），那么你就很好了。因此，取决于
FooComp的外观以及您调用的find...std::set::find()will useFooComp, as long as the double does not form part of that comparison, it should be fine.std::findrequiresoperator==, so again depends if you've define this and what that includes, as long as it does not include the double (or includes the double in a sensible way), then you're good.So, depends what
FooComplooks like and whichfindyou call...比较器将用于查找集合中的指定项目。
The comparator will be used to find the specified item in the set.
比较类将用于维护
set的排序以及find()。The comparison class will be used to maintain the
setsorted and tofind()also.