c++ - 类的 unique_copy 无法识别运算符<

Question

我无法理解编译器错误消息关于 unique_copy 的含义:

error C2672: 'operator __surrogate_func': no matching overloaded function found

std::unique_copy(begin(collection_raw), end(collection_raw), back_inserter(collection_sorted));

我使用 less 运算符提交员工集合，如下所示:

struct employee
{
    std::string name;
    std::string address;
};

// Employees comparer
bool operator<(const employee& item1, const employee& item2)
{
    return item1.name < item2.name;
}

错误消息来自 Visual Studio 2019，我不确定它是什么意思。

下面是一个编译示例，因为我注释掉了 std::unique_copy:

#include <iostream>
#include <vector>
#include <list>
#include <algorithm>

struct employee
{
    std::string name;
    std::string address;
};

// Employee comparer
bool operator<(const employee& item1, const employee& item2)
{
    return item1.name < item2.name;
}

// Copy the raw vector of employees into a list of sorted and unique employees
void copy_uniq_elements(std::vector<employee>& collection_raw, std::list<employee>& collection_sorted)
{
    // use operator< to order items
    std::sort(begin(collection_raw), end(collection_raw));

    // Don't copy adjacent equal elements
    // error C2672:  'operator __surrogate_func': no matching overloaded function found
    // std::unique_copy(begin(collection_raw), end(collection_raw), back_inserter(collection_sorted));
}

int main()
{
    std::vector<employee> staff { {"Bob", "11 rue de longueil"},
                                  {"Arnold", "22 rue de la retraite"},
                                  {"Gilbert", "33 rue de belle-humeur"},
                                  {"Xavier", "11 rue de longueil"} };

    std::list<employee> staff_sorted;
    copy_uniq_elements(staff, staff_sorted);

    for (const auto item : staff_sorted)
    {
        std::cout << item.name << std::endl;
    }

    return 0;
}

Answer 1

为员工重载 == operator。

bool operator==(const employee& item1, const employee& item2)
{
    // something.
}

或将二进制谓词传递给 std::unique_copy

std::unique_copy(begin(collection_raw), end(collection_raw), back_inserter(collection_sorted), 
         [] (auto& b, auto& c) { return b.name == c.name; } );