Passing a member function as standard function callback

Question

I\'ve been struggling for hours with the same part of the code, and I cannot find any answer that can guide me.

I\'m using a library, and a method requires to pass a cal

Answer 1

Member functions take *this pointer as a first parameter, so your function signature is actually:

void(HouseKeeper*, char*, uint8_t*, unsigned int)

While std::function in library setCallback function takes:

std::function<void(char*, unsigned char*, unsigned int)>.

You have to change your uint8_t* to unsigned char* in your callback second parameter (thanks Daniel H), and also get rid of implicit *this.

• You can use std::bind to bind *this pointer to match setCallback() signature:

  std::function<void(char*, uint8_t*, unsigned int)> yourFunction = std::bind(&HouseKeeper::callback, this, _1, _2, _3);
  
  library.setCallback(yourFunction);
  

• Or wrap your call in lambda function:

  std::function<void(char*, uint8_t*, unsigned int)> yourFunction = [=](char* topic, uint8_t* payload, unsigned int length) {
      this->callback(topic, payload, length);
  }
  
  library.setCallback(yourFunction);
  

Answer 2

The "classic" way to use callbacks is to declare your callback function static.