In the C file in simplesample_mqtt.c, which connects Arduino to the Azure IoT hub, I need to use the IRsend and IrRemoteESP8266 libraries to send an infrared signal with Azure IoT hub.

 #include <IRremoteESP8266.h>
 #include <IRsend.h>
 IRsend irsend(10); // An IR LED is controlled by GPIO pin 4 (D2)

I don't have any problem when I use this code in my main Arduino file. But when I use these includes in a C file (simplesample_mqtt.c), I get this error from line 3: "unknown type name 'IRsend'".

enter image description here

error full info :

Arduino: 1.8.2 (Windows 10), Board: "NodeMCU 0.9 (ESP-12 Module), 80 MHz, 115200, 4M (3M SPIFFS)"

In file included from sketch\simplesample_mqtt.c:29:0:

C:\Program Files (x86)\Arduino\libraries\IRremoteESP8266\src/IRsend.h:29:1: error: unknown type name 'class'

class IRsend {

C:\Program Files (x86)\Arduino\libraries\IRremoteESP8266\src/IRsend.h:29:14: error: expected '=', ',', ';', 'asm' or 'attribute' before '{' token

class IRsend {

simplesample_mqtt.c:31: error: unknown type name 'IRsend'

IRsend irsend(10); // An IR LED is controlled by GPIO pin 4 (D2)

simplesample_mqtt.c:31: error: expected declaration specifiers or '...' before numeric constant

IRsend irsend(10); // An IR LED is controlled by GPIO pin 4 (D2)

exit status 1
unknown type name 'IRsend'

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  • 1
    error: unknown type name 'class' Classes only exist in C++. Try changing the file extension to ".cpp".
    – 001
    Commented Aug 13, 2017 at 22:08
  • And if that doesn't work, make sure the class in IRremoteESP8266.h has a ; after the closing } Commented Aug 14, 2017 at 9:21

1 Answer 1


I solved this problem. The reason for this is because main Arduino is c++ and simplesample_mqtt.c is c code and we have to use c++ code in c code:

In main Arduino file you have to declare function like this :

extern "C" void TurnOn();
void TurnOn()
    digitalWrite(RELAY_SONOFF, HIGH);     
    digitalWrite(LED_SONOFF, HIGH);

and use this function in c code:

void TurnOn();
EXECUTE_COMMAND_RESULT TurnOn(ContosoAnemometer* device)
    (void)printf("Turning fan on.\r\n");

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