my code was

#include <iostream>
#include <list>
#include <functional>

using namespace std;

void tes(std::string s)
{
    cout << "tes " << s << '\n';
}

void tes2(std::string s)
{
    cout << "tes " << s << '\n';
}

void tes3(std::string s)
{
    cout << "tes " << s << '\n';
}


int main()
{
    using FuncType = std::function<void(std::string&)>;
    std::list<std::pair<int, FuncType>> events =
    { 
        {1, std::bind(tes, "1")}, 
        {2, std::bind(tes2, "2")},
        {3, std::bind(tes3, "3")} };
    
    int t = 1;
    auto remove_func = [&t](std::pair<int, FuncType> pair)
        -> bool
    {
        return pair.first == t;
    };
    
    events.remove_if(remove_func);
    for (auto ev : events)
    {
        std::cout << ev.first << ' ' ;
        ev.second;
    }
    
}

the result just display ev.first, but not the ev.second. what happened?? how to resolve this problem?? i mean display the string in FuncType function such "2" and "3". or fixed this code properly to work to display each.

CodePudding user response：

Fix the misprint:

    std::cout << ev.first << ' ' << ev.second;

CodePudding user response：

There are a couple of issues in the posted code

// ...
void tes(std::string s)
{ //     ^^^^^^^^^^^^^
}
// ...
using FuncType = std::function<void(std::string&)>;
//                                  ^^^^^^^^^^^^ 
std::list<std::pair<int, FuncType>> events =
{ 
    {1, std::bind(tes, "1")}, 
    {2, std::bind(tes2, "2")},
    {3, std::bind(tes3, "3")}
//      ^^^^^^^^^^^^^^^^^^^^ 
};

The functions like tes have one parameter of type std::string, the alias FuncType is a std::function with one parameter of type std::string&, but the pairs in events are assigned the results of std::bind, which have zero parameters (they are, well, binded).

Moreover, in the printing loop

for (auto ev : events)
{
    std::cout << ev.first << ' ' ;
    ev.second;                       // <- This does nothing, it should be a call.
}

The fix¹ is straightforward:

using FuncType = std::function<void(void)>;
//                                 ^^^^^^

// ...

for (auto ev : events)
{
    std::cout << ev.first << ' ' ;
    ev.second();
    //       ^^
}

^{1) https://godbolt.org/z/5f8srj9va}