Describe the problem

A stray curly-brace in // comments or #if (false) sections causes the function prototypes generated during the "sketch pre-processing" stage of the compilation operation to be incorrectly prefixed with extern "C"

For example:

extern "C" void setup();

To reproduce

Compile the following sketch:

#if (false) // The below lines should not be enabled, and so should not have any effect 
#error "Should not get to here"
// {               // either delete this line,
// extern "C" {}   // or delete this line, and the below code is compiled fine!
#endif

void setup() {
  Serial.begin(74880);
}

void loop() {
  delay(5000);
  Serial.println("Hello");
}

Examine the .cpp file generated by the compilation.

🐛 Generated function prototypes are prefixed with extern "C"

Compile the following sketch:

#if (false) // The below lines should not be enabled, and so should not have any effect 
#error "Should not get to here"
// {               // either delete this line,
// extern "C" {}   // or delete this line, and the below code works fine!
#endif

ADC_MODE(ADC_VCC);

void setup() {
  Serial.begin(74880);
}

void loop() {
  delay(5000);
  Serial.print("raw_battery (should be between 3000 and 3300)="); Serial.println(ESP.getVcc());
  // unless you DELETE one of the above two COMMENT lines, you will get "=65535" and not "=3017"
}

Examine the .cpp file generated by the compilation.

🐛 Generated function prototypes are prefixed with extern "C"

Expected behavior

Generated function prototypes should be correct regardless of the contents of comments:

void setup();

Arduino CLI version

Original report

Arduino IDE v1.8.16

Last verified with

d563755

Operating system

Windows

Operating system version

11

Additional context

I note that there are several discussions regarding curly-braces for Arduino IDE but none of these seem to cover this specific issue:

• https://forum.arduino.cc/t/ide-bug-with-braces-that-arent-part-of-the-code/206063
• https://forum.arduino.cc/t/curly-braces-in-strings-or-quotes/212575

Additional reports

• https://forum.arduino.cc/t/arduino-ide-causes-a-compilation-error-even-if-extern-c-is-inside-a-comment/1126819

Related

• Generated prototype incorrectly prefixed with extern "C" when using extern "C" { ... } to mix C functions in an .ino file. #1618

Issue checklist

• I searched for previous reports in the issue tracker
• I verified the problem still occurs when using the nightly build
• My report contains all necessary details