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How to use 'this' reference in lambda function and still match MQTT-TLS library definition

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0

I'm passing a lambda function as a callback to the MQTT-TLS library.

Here is the MQTT-TLS class constructor declaration:

MQTT(char* domain, uint16_t port, void (*callback)(char*,uint8_t*,unsigned int));

I call the MQTT-TLS like this:

void MQTTMsgs::init() 
 char addr[] = "172.20.10.3";

 this->mqttClient = new MQTT(addr, 1883, [](char* topic, byte* payload, unsigned int length) 
 // inside callback
 );

This code works fine. Compiles and life is good. But the problem is, I need access to 'this' inside of the callback. So then, I add 'this' as a reference of the lambda function like so:

this->mqttClient = new MQTT(addr, 1883, [this](char* topic, byte* payload, unsigned int length) 
 this->accessOtherPropsEtcEtc();
);

And this is where it slburps out. I get this error on compiling:

error: no matching function for call to 'MQTT::MQTT(char [12], int, MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int
error: note: no known conversion for argument 3 from 'MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int)>' to 'void (*)(char*, uint8_t*, unsigned int) aka void (*)(char*, unsigned char*, unsigned int)'

My question is, why does it compile just fine with a lambda function, but errors out when that same lambda function is passed in 'this' as a reference? My guess is that somehow the g++ compiler is setting the type as MQTT instead of void or 'callback' (or something) and therefore the MQTT function definition isn't matching it. Just not sure how the compiler is seeing this. Any ideas on how I can tweak this to match and work with the MQTT-TLS definition?

Still not fluent in C++ yet. Lots of minutia in this language.

c++ lambda arduino g++

share|improve this question

asked Mar 8 at 4:38

risingtigerrisingtiger

368114

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Possible duplicate of Passing capturing lambda as function pointer
  
  – S.M.
  Mar 8 at 4:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  One of the answers in the proposed duplicate tells you how to resolve this issue.
  
  – P.W
  Mar 8 at 5:24
  

  
  
  
  

add a comment | 

0

I'm passing a lambda function as a callback to the MQTT-TLS library.

Here is the MQTT-TLS class constructor declaration:

MQTT(char* domain, uint16_t port, void (*callback)(char*,uint8_t*,unsigned int));

I call the MQTT-TLS like this:

void MQTTMsgs::init() 
 char addr[] = "172.20.10.3";

 this->mqttClient = new MQTT(addr, 1883, [](char* topic, byte* payload, unsigned int length) 
 // inside callback
 );

This code works fine. Compiles and life is good. But the problem is, I need access to 'this' inside of the callback. So then, I add 'this' as a reference of the lambda function like so:

this->mqttClient = new MQTT(addr, 1883, [this](char* topic, byte* payload, unsigned int length) 
 this->accessOtherPropsEtcEtc();
);

And this is where it slburps out. I get this error on compiling:

error: no matching function for call to 'MQTT::MQTT(char [12], int, MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int
error: note: no known conversion for argument 3 from 'MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int)>' to 'void (*)(char*, uint8_t*, unsigned int) aka void (*)(char*, unsigned char*, unsigned int)'

My question is, why does it compile just fine with a lambda function, but errors out when that same lambda function is passed in 'this' as a reference? My guess is that somehow the g++ compiler is setting the type as MQTT instead of void or 'callback' (or something) and therefore the MQTT function definition isn't matching it. Just not sure how the compiler is seeing this. Any ideas on how I can tweak this to match and work with the MQTT-TLS definition?

Still not fluent in C++ yet. Lots of minutia in this language.

c++ lambda arduino g++

share|improve this question

asked Mar 8 at 4:38

risingtigerrisingtiger

368114

• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  Possible duplicate of Passing capturing lambda as function pointer
  
  – S.M.
  Mar 8 at 4:48
  

  
  
  
  


• 
  
  
  

  
  1
  

  
  
  
  
  
  

  
  
  One of the answers in the proposed duplicate tells you how to resolve this issue.
  
  – P.W
  Mar 8 at 5:24
  

  
  
  
  

add a comment | 

I'm passing a lambda function as a callback to the MQTT-TLS library.

Here is the MQTT-TLS class constructor declaration:

MQTT(char* domain, uint16_t port, void (*callback)(char*,uint8_t*,unsigned int));

I call the MQTT-TLS like this:

void MQTTMsgs::init() 
 char addr[] = "172.20.10.3";

 this->mqttClient = new MQTT(addr, 1883, [](char* topic, byte* payload, unsigned int length) 
 // inside callback
 );

This code works fine. Compiles and life is good. But the problem is, I need access to 'this' inside of the callback. So then, I add 'this' as a reference of the lambda function like so:

this->mqttClient = new MQTT(addr, 1883, [this](char* topic, byte* payload, unsigned int length) 
 this->accessOtherPropsEtcEtc();
);

And this is where it slburps out. I get this error on compiling:

error: no matching function for call to 'MQTT::MQTT(char [12], int, MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int
error: note: no known conversion for argument 3 from 'MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int)>' to 'void (*)(char*, uint8_t*, unsigned int) aka void (*)(char*, unsigned char*, unsigned int)'

My question is, why does it compile just fine with a lambda function, but errors out when that same lambda function is passed in 'this' as a reference? My guess is that somehow the g++ compiler is setting the type as MQTT instead of void or 'callback' (or something) and therefore the MQTT function definition isn't matching it. Just not sure how the compiler is seeing this. Any ideas on how I can tweak this to match and work with the MQTT-TLS definition?

Still not fluent in C++ yet. Lots of minutia in this language.

c++ lambda arduino g++

share|improve this question

asked Mar 8 at 4:38

risingtigerrisingtiger

368114

MQTT(char* domain, uint16_t port, void (*callback)(char*,uint8_t*,unsigned int));

void MQTTMsgs::init() 
 char addr[] = "172.20.10.3";

 this->mqttClient = new MQTT(addr, 1883, [](char* topic, byte* payload, unsigned int length) 
 // inside callback
 );

this->mqttClient = new MQTT(addr, 1883, [this](char* topic, byte* payload, unsigned int length) 
 this->accessOtherPropsEtcEtc();
);

error: no matching function for call to 'MQTT::MQTT(char [12], int, MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int
error: note: no known conversion for argument 3 from 'MQTTMsgs::MQTTMsgs()::<lambda(char*, byte*, unsigned int)>' to 'void (*)(char*, uint8_t*, unsigned int) aka void (*)(char*, unsigned char*, unsigned int)'

share|improve this question

asked Mar 8 at 4:38

risingtigerrisingtiger

368114

share|improve this question

asked Mar 8 at 4:38

risingtigerrisingtiger

368114

asked Mar 8 at 4:38

risingtigerrisingtiger

368114

asked Mar 8 at 4:38

risingtigerrisingtiger

368114