问题描述
为什么以下不起作用?:
why does the following not work?:
MyClass *c = new MyClass();
std::vector<MyClass> myVector;
std::find(myVector.begin(), myVector.end(), *c)
这会带来错误.我不记得确切的错误,抱歉,但它说像 MyClass 和 const MyClass 这样的东西不能被 Operator ==
This will bring an error. I cannot remember the exact error, sorry for that, but it said something like MyClass and const MyClass cannot be compared by the Operator==
但是,如果我对非类数据类型而不是MyClass"执行相同的操作,则一切正常.那么如何用类正确地做到这一点?
However if I do the same thing with non-class datatypes instead of a "MyClass", everything works fine.So how to do that correctly with classes?
推荐答案
std::find
文档来自 http://www.cplusplus.com/reference/algorithm/find/:
template InputIterator find (InputIterator first, InputIterator last, const T& val);
在范围内查找值返回指向范围 [first,last) 中第一个元素的迭代器,该元素比较等于 val.如果没有找到这样的元素,函数最后返回.
Find value in rangeReturns an iterator to the first element in the range [first,last) that compares equal to val. If no such element is found, the function returns last.
该函数使用 operator==
将各个元素与 val 进行比较.
编译器不会为类生成默认的operator==
.您必须定义它才能将 std::find
与包含类实例的容器一起使用.
The compiler does not generate a default operator==
for classes. You will have to define it in order to be able to use std::find
with containers that contain instances of your class.
class A
{
int a;
};
class B
{
bool operator==(const& rhs) const { return this->b == rhs.b;}
int b;
};
void foo()
{
std::vector<A> aList;
A a;
std::find(aList.begin(), aList.end(), a); // NOT OK. A::operator== does not exist.
std::vector<B> bList;
B b;
std::find(bList.begin(), bList.end(), b); // OK. B::operator== exists.
}
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