[英]find struct as value in std::map
I am trying to use std::map::count()
to find a value, which is a custom struct, in the dictionary. 我正在尝试使用
std::map::count()
在字典中查找一个值,这是一个自定义结构。 The following code will not compile 以下代码无法编译
typedef struct myStruct
{
int x;
int y;
}MyStruct;
MyStruct instace;
instace.x = 0;
instace.y = 1;
map<unsigned int, myStruct> myMap;
myMap[0] = instace;
if(myMap.count(instace) == 1)
{
//do something
}
and this is the error I get 这是我得到的错误
no instance of overloaded function "std::map<_Kty, _Ty, _Pr, _Alloc>::count
[with _Kty=unsigned int, _Ty=myStruct, _Pr=std::less<unsigned int>,
_Alloc=std::allocator<std::pair<const unsigned int, myStruct>>]" matches the
argument list
I think the compiler does not know how to compare my struct. 我认为编译器不知道如何比较我的结构。 The third argument in the declaration of a map takes a compare function, I tried to create a compare function and pass it to the third argument in declaration like the following
映射声明中的第三个参数采用了compare函数,我尝试创建一个compare函数并将其传递给声明中的第三个参数,如下所示
struct comparer
{
bool operator()(MyStruct const& Left, MyStruct const& Right) const {
return (Left.x == Right.x && Left.y == Right.y);
}
};
map<unsigned int, myStruct, comparer> myMap;
but when I do myMap.count()
, I get similar error. 但是当我执行
myMap.count()
,出现类似的错误。
I have searched google using every possible way I could describe the problem, but I did not find the answer. 我已经用我能描述问题的所有可能方式搜索了google,但没有找到答案。 Can someone tell me how to solve this problem?
有人可以告诉我如何解决这个问题吗? Thanks!
谢谢!
Looking at std::map::count , count takes the key and return the number of elements associated with that key. 查看std :: map :: count ,count获取键并返回与该键关联的元素数。 That means that your code should be:
这意味着您的代码应为:
if(myMap.count(0) == 1) // for key == 0
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