Prototypes for methods with default arguments are not generated [imported]

[cmaglie]

This is Issue 386 moved from a Google Code project.
Added by 2010-10-23T13:23:50.000Z by [email protected].
Please review that bug for more context and additional comments, but update this bug.

Original labels: Type-Defect, Priority-Medium, Component-PreProcessor

Original description

Steps to reproduce the issue:

STEP 1. Insert the following code into a blank sketch:

void setup() {
  test(42);
  test2(42);
}

void loop() {}
void test(int arg) {};
void test2(int arg = 0) {};

STEP 2: Click the verify button and observe the error message:

DefaultArgBugDemo.cpp: In function 'void setup()':
DefaultArgBugDemo:2: error: 'test2' was not declared in this scope

STEP 3:
Examine the generated *.cpp file and observe that a prototype has been generated for test1 but not test2:

#include "WProgram.h"
void setup();
void loop();
void test(int arg);
void setup() {
  test(42);
  test2(42);
}

void loop() {}
void test(int arg) {};
void test2(int arg = 0) {};

What is the expected output? What do you see instead?

You would expect a prototype to be generated for test2.

What version of the Arduino software are you using? On what operating
system? Which Arduino board are you using?

Tested in 0018 and 0021. Running on Win7 Home Premium (though the issue likely exists on all platforms)

Please provide any additional information below.

Of course the workaround is relatively simple (just define the prototype yourself) but it would be nice for all methods to be treated equally.

[ffissore]

Please checkout this thread [1] on devs mailing list and try one of the linked IDEs. It should fix the problems reported in this issue
[1] https://groups.google.com/a/arduino.cc/forum/#!topic/developers/4X2T3rCxXWM

[ffissore]

With #3779 the preprocessed code is now

#include <Arduino.h>
#line 1
#line 1 "sketch_sep11c.ino"
void setup();
void loop();
void test(int arg);
void test2(int arg = 0);
#line 1
void setup() {
  test(42);
  test2(42);
}

void loop() {}
void test(int arg) {};
void test2(int arg = 0) {};

which now fails with

sketch_sep11c.ino: In function 'void test2(int)':
sketch_sep11c.ino:8:23: error: default argument given for parameter 1 of 'void test2(int)' [-fpermissive]
sketch_sep11c.ino:4:6: error: after previous specification in 'void test2(int)' [-fpermissive]
default argument given for parameter 1 of 'void test2(int)' [-fpermissive]

Can you help spot the error? Code looks good to me

[cmaglie]

The default argument must be defined only once per compilation unit, for example you can't write:

void test(int a=0);
void test(int a=0) { /* empty */ }

even if the default argument = 0 is the same.
To fix it, it seems that you can arbitrarily choose to drop the default argument in the prototype or in the implementation, I've tried to compile with g++:

void test(int a);
void test(int a=0) { /* empty */ }

and

void test(int a=0);
void test(int a) { /* empty */ }

and both compiles fine.

[ffissore]

Now I remember an old chat about it. I chose not to handle default args. Reason is that the correct way of using default args is to have the prototype list them, as in @cmaglie second example

void test(int a=0);
void test(int a) { /* empty */ }

However this implies that preprocessor must change original source code: I mean not just inserting code, but changing existing code. This is dangerous as we don't have a source code manipulation tool powerful enough to handle all the possible cases (eg: functions defined on multiple lines, spaces, comments between arguments on multi lines...)

So this is a wontfix. If you want to use default arguments, you have to define the prototype yourself. #3779 is now smart enough to understand that a function with default args already has its prototype and leave it alone