constexpr weirdness

Projects Programming
1

Hey all.

I'm experiencing some weirdness with constexpr in Arduino and am hoping someone here can shed some light. Just wanting to at first toy around with this c++11 feature I tried a trivial example:

constexpr bool oneTrue(bool a, bool b) { return a || b; }

and I get an error stating 'constexprbool does not name a type.' (as is, concatenation between constexpr and bool is in the error message.)

Here's what I've tried:

  • I fooled around with changing return type and inputs to boolean
  • I moved the function into a separate compilation unit
  • I checked that -std=gnu++11
  • I was using Arduino 1.6.7 and downgraded to 1.6.6

I also tried creating a constexpr which returned an int and a float and both of those compile just fine.

Does anyone have any insight as to why this is happening or better, how to fix it?

Thanks in advance!

2

Assuming there are no other errors in the code (that you did not post), maybe constexpr is not supported by gcc-avr. Alternative is the use of a normal function or a macro

#define oneTrue(a, b) ((a) || (b))

void setup()
{
  bool c = false, d = true;

  Serial.begin(9600);
  Serial.println(oneTrue(c,d));
}

void loop()
{
  // put your main code here, to run repeatedly:

}

Note: tested in VS2012 C++ with ordinary printf

3

Hello,

jjtjp:
and I get an error stating 'constexprbool does not name a type.' (as is, concatenation between constexpr and bool is in the error message.)

Split the line...

constexpr
bool oneTrue(bool a, bool b) { return a || b; }

void setup() { }
void loop() { }

However...

I checked that -std=gnu++11

...is very likely the problem.

4

constexpr is obviously somewhat supported since the following compiles and works as it ought:

constexpr int three() { return 3; }

void setup() {
    Serial.println(three());
}

void loop() {
    // empty
}

-std=gnu++11 is the Arduino default since the next release after July 2014.
See: