Optional function parameters

[mattallen37]

I know that you can have optional parameters for functions like this:

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int foo(int x, int y, int z = 12){
  return x+y+z;
}

and you could call it with something like this:

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NumOut(0, LCD_LINE1, foo(25, 7));

or

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NumOut(0, LCD_LINE1, foo(25, 7, 73));

And I assume you can do something like this as well:

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void txt_out(string text = "Hi!"){
  TextOut(0, LCD_LINE1, text);
}

and call it like this:

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txt_out(); //Should display "Hi!"

or

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txt_out("Hello!"); //Should display "Hello!"

What if you have a function that optionally "sets" information upon return. I want an option to supply a variable that gets written to. Something like this:

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int add(int x, int y, int & d_result){
  d_result = (x+y)*2;
  return d_result/2;
}

Normally you would call it like this:

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int Double;
NumOut(0, LCD_LINE1, add(13, 2, Double));//Should display 15
NumOut(0, LCD_LINE2, Double);            //Should display 30

However, what if I don't want to provide a variable for "d_result"? What if all I care about is the returned value? How can I do something like this?

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NumOut(0, LCD_LINE1, add(13, 2));

[mattallen37]

It's sort of like the idea of calling a function, but not giving it a place to return the value. Like

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foo(25, 7);

I know that In this case it would be pointless to call the function, as it doesn't do anything helpful.

[nxtboy]

Does this work?

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int TEMP = 2;

int add(int x, int y, int &d_result = TEMP){
  d_result = (x+y)*2;
  return d_result/2;
}

If not, http://stackoverflow.com/questions/1059 ... rence-in-c is relevant

[pepijndevos]

I heard that NXC implements pass-by-reference by copying a global variable, so if you just do that yourself, you can decide to copy or not to copy.

[HaWe]

matt,
could you pls explain what you're trying to do, especially what for?
E.g., are you trying to implement function overloading?
Or are you trying to pass functions as variable function parameters?

[mattallen37]

I can't really test it now.

What I want, is the ability to choose if I want to provide a string to get written to. Like this:

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int AddString(string x, string y, string & z){
  z = x + y;
  return StrLen(z);
}

I could call that by using something like this:

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string full;
NumOut(0, LCD_LINE1, AddString("Hello", " World!", full));
TextOut(0, LCD_LINE2, full);

but what if I don't want the resulting string, just the length? I want to be able to use the function like this:

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NumOut(0, LCD_LINE1, AddString("Hello", " World!"));

[HaWe]

did you already try strcat instead of "+"?

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strcat(z,x);
strcat(z,y);
return strlen(z);

IIRC there was an issue about adding strings bei "+".

edit:
it works for me! (shown is "12"):

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int AddString(string x, string y, string & z){
  strcat(z,x);
  strcat(z,y);
  return strlen(z);
}

task main() {
  string full="";
  int l=AddString("Hello ", "world!", full );
  printf("%d", l);
  while(1);
}

using NumOut it works also inline (I wish it did also with printf):

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int AddString(string x, string y, string & z){
  strcat(z,x);
  strcat(z,y);
  return strlen(z);
}

task main() {
  string full="";
  int l;
  NumOut(0,0,AddString("Hello ", "world!", full ));
  while(1);
}

[afanofosc]

Matt,

I would simply try it and see what happens. Like this:

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int AddString(string x, string y, string & z = ""){
  z = x + y;
  return StrLen(z);
}

task main()
{
  string testing;
  NumOut(0, LCD_LINE1, AddString("hello", "world"));
  NumOut(0, LCD_LINE2, AddString("hello", "world", testing));
  TextOut(0, LCD_LINE3, testing);
}

Does it compile? Does it work? Does the F12 code look right? In my case the answer is Yes to all three questions. This is not valid C/C++ code, however.

John Hansen

[HaWe]

aah, now I understand what matt was trying!
not returning just the length was the point but passing 2 or 3 strings alternatively.
That string & z = "" thing is a good trick, I'll have to keep that in my mind.

[mattallen37]

Yes it does work! Thank you very much!