unresolved overloaded function error when binding to std::operator==

Question

I am trying to bind to bool std::operator==(const std::string&, const std::string&), but I'm getting an error that I hope somebody can help me with.

std::string v1 = "foo";
std::string v2 = "foo";

bool r = 
    std::bind(
        static_cast<bool(*)(const std::string&, const std::string&)>(&std::operator== ),
        std::placeholders::_1,
        std::cref(v1))(v2);


error: invalid static_cast from type '<unresolved overloaded function type>' to type 'bool (*)(const string&, const string&) {aka bool (*)(const std::basic_string<char>&, const std::basic_string<char>&)}'
             &std::operator== ), 
                              ^

example: ideone.com

Isn't your inner voice telling you that probably you shouldn't be using this stuff? `std::bind` was meant to be a joke, not something to be used for real... — 6502, Feb 01 '15 at 20:18

score 3 · Accepted Answer · answered Feb 01 '15 at 20:10

Disambiguating std::operator== solves your problem, but it isn't the cleanest looking code:

bool r = 
        std::bind(
            static_cast<bool(*)(const std::string&, const std::string&)>(operator==<char, std::string::traits_type, std::string::allocator_type>),
            std::placeholders::_1,
            std::cref(v1))(v2);

score 2 · Answer 2 · edited May 23 '17 at 10:27

2

Pradhan gives you the correct syntax for using bind in this spot. Which seems like a great reason to not use bind in this spot and to prefer a lambda:

bool r = [&v1](const std::string& rhs){
    return rhs == v1;
}(v2);

edited May 23 '17 at 10:27

Community

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answered Feb 01 '15 at 20:15

Barry

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unresolved overloaded function error when binding to std::operator==

2 Answers2