CODEWITHSUNDEEP
c++lambdac++11
Ghita
Ghita

Reputation: 4505

C++ 11 - bind a C style callback to a class member function

Using code from http://ideone.com/5MHVz I am curious how is it possible that I can bind a lambda function (inline) to a C style function pointer but I cannot do this with a class function even if there is no state involved. It must be some fundamental difference but I don't understand how lambda binding is possible in this case then (there is a conceptual this to lambda generated code also). Is there a workaround ?

Code bellow:

#include <iostream>
#include <functional>
using namespace std;

typedef int (*http_cb) (int*);

struct http_parser_settings {
  http_cb      on_message_begin;
};

class HttpParser
{
  int OnMessageBegin(int* val){}

  HttpParser()
  {
    http_parser_settings settings;
    //settings.on_message_begin = std::bind(&HttpParser::OnMessageBegin, this, std::placeholders::_1); -- this one does not compile
   settings.on_message_begin = [](int* p){ return 0;};
  }
};

int main() {

}

Upvotes: 1

Views: 904

Answers (2)

Coder_Dan
Coder_Dan

Reputation: 1872

You can store lambdas in std::function objects even in MSVC2010, so there must be a way to get a raw function pointer. I've never delved into the details of how it works, but have certainly used this feature before.

Upvotes: -1

Kerrek SB
Kerrek SB

Reputation: 476950

Non-capturing lambdas can be converted to function pointers. They're essentially free functions, so there's no problem.

Upvotes: 3

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