c++ - STL set_intersection 运行时错误

Question

我正在编写一个代码，根据对象的 ID 将两个对象 vector 相交。我收到运行时错误。我试图找出问题所在，但不知道为什么？你能帮我吗？

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

using namespace std;

class Mclass
{
    public:
    uint64_t id;
    string name;
    Mclass(uint64_t _id, string _name)
    {
       id = _id;
       name = _name;
    }
    bool operator<(const Mclass &info) const
    {
       return (this->id < info.id);
    }

    Mclass operator=(const Mclass &source)
    {
       this->id = source.id;
       this->name = source.name;
       return *this;
    }

    bool operator==(const Mclass &info) const
    {
       return (this->id > info.id);
    }
};

int main()
{
    vector <Mclass> v1;
    vector <Mclass> v2;
    vector <Mclass> v_in;

    v1.push_back(Mclass(1, "a1"));
    v1.push_back(Mclass(2, "a2"));
    v1.push_back(Mclass(5, "a5"));

    v2.push_back(Mclass(2, "b2"));
    v2.push_back(Mclass(3, "b3"));
    v2.push_back(Mclass(5, "b5"));

    for(int i = 0; i < v1.size(); ++i)
    {
        cout << v1[i].id << ": " << v1[i].name << endl;
    }

    for(int i = 0; i < v2.size(); ++i)
    {
        cout << v2[i].id << ": " << v2[i].name << endl;
    }

    set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(), v_in.begin(),
                     [](const Mclass& arg1, const Mclass& arg2)
    {

        return (arg1.id == arg2.id);
    });

    for(int i = 0; i < v_in.size(); ++i)
    {
        cout << v_in[i].id << ": " << v_in[i].name << endl;
    }

    return 0;
}

gdb 日志

(gdb) run
Starting program: /mnt/DATA/Dropbox/ExperimentalCode/CPP/a.out 
1: a1
2: a2
5: a5
2: b2
3: b3
5: b5

Program received signal SIGSEGV, Segmentation fault.
0x08049641 in Mclass::operator=(Mclass const&) ()
(gdb) bt
#0  0x08049641 in Mclass::operator=(Mclass const&) ()
#1  0x0804949a in __gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass,  std::allocator<Mclass> > > std::set_intersection<__gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass, std::allocator<Mclass> > >, __gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass, std::allocator<Mclass> > >, __gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass, std::allocator<Mclass> > >, main::{lambda(Mclass const&, Mclass const&)#1}>(__gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass, std::allocator<Mclass> > >, __gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass, std::allocator<Mclass> > >, __gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass, std::allocator<Mclass> > >, __gnu_cxx::__normal_iterator<Mclass*, std::vector<Mclass, std::allocator<Mclass> > >, main::{lambda(Mclass const&, Mclass const&)#1}, main::{lambda(Mclass const&, Mclass const&)#1}) ()
#2  0x08049114 in main ()

Answer 1

您正在尝试将对象写入空 vector 。你可能打算使用

std::set_intersection(v1.begin(), v1.end(), v2.begin(), v2.end(),
                      std::back_inserter(v_in),
                     [](const Mclass& arg1, const Mclass& arg2)
    {

        return (arg1.id < arg2.id);
    });

请注意将 std::back_inserter() 添加到输出范围。此外，正如 Igor Tandetnik 在评论中指出的那样，谓词必须在对象上定义严格的弱顺序，而不是相等关系。请注意，需要对输入进行排序(在您的示例中，您将它们创建为已排序)。