Default argument

Projects Programming
1

I am using Windows10. In 1.8x I used a default argument for a function, as in:
int takeAction(int DoIt, waitime=_defaultWaitTime)
{ .... }
If I didn't pass in an argument for waitime, then the default was used, just as in C++.

With IDE 2.0 BETA 9, I get an error with all calls to the function that don't pass in the second argument. This was code that worked fine with V 1.8x.

2

What is the error ?

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3

Is not valid, you need to give the second argument a type.

4

I did more analysis. The error I get is "Error: too few arguments to function 'int takeAction(int, int)' and it refers only to a block of code where I define the takeAction() function because the compiler complains it isn't in scope. My code is broken down into 3 tabs. The takeAction() function is in one of them. It is invoked by a function in the same tab, and there I've no problem. It was to solve a different issue that I put a call to the takeAction() function in another tab. However, I'd thought the different tabs was just for ease of programming, that everything was all at the same level. I never before had an error caused by invoking a function from one tab to another.

Getting this scope error, I declared takeAction(int, int) outside the code -- before setup and loop(), right after the includes. Because the second parameter (an int) isn't shown to be optional in this declaration, is the reason I got the error. Please note that in the function implementation I specify int, int as in takeAction(int doIt, int waitime=defaultWait);

I think this issue is a quirk that's easily solved by passing a 0 for the second parameter. I will most likely research the issue some more, but at least I have a solution. I think I need educate myself on how to declare an extern function with a default parameter.

5

If you give a default argument to a function in a sketch, the parser does not create a prototype declaration, so it can not compile without write prototype in myself.
It's success to compile if you write that function before actually use it.

I thought that Arduino keeps in mind that we can easily write a function without having to good knowledge about the prototype and C++.
But if you want to create a function with default arguments in C++, you need to declare the default value only in the prototype.

However, I think this goes against the Arduino principle of hiding prototype declarations from users.

6 
int mysum(int x, int y = 20) {
  return x + y;
}
void setup() {
  Serial.begin(9600);
  Serial.println(mysum(10));
}
void loop() {
}

It can be compiled.
Because no prototype declaration required.

But

void setup() {
  Serial.begin(9600);
  Serial.println(mysum(10));
}
void loop() {
}
int mysum(int x, int y = 20) {
  return x + y;
}

It can't be compiled.
Because the parser doesn't generate a prototype declaration.

But

int mysum(int , int = 20);
void setup() {
  Serial.begin(9600);
  Serial.println(mysum(10));
}
void loop() {
}
int mysum(int x, int y) {
  return x + y;
}

It can be compiled.
Because it prototype declaration myself.

7

Please provide a complete minimal demonstration of the problem.

.ino file tabs are all concatenated into a single file by the sketch preprocessor before compiling. The order of concatenation is the file that matches the sketch folder name, followed by the other .ino files in lexicographical order.

8

Recent discussion on the subject (which even included the use of tabs, even though that is not relevant) here:
https://forum.arduino.cc/t/tabs-in-arduino-ide/881167/27

9

@pert

Thanks for the link.
I'll follow that topic.

Well sure, functions with default values are rarely used.
It's often used in class but...

10

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