Help using Serial.println inside a function

General
1

Hi guys, I’ve been trying to do something that is probably really simple but I can’t find anywhere how to properly do it. I basically want to use Serial.println inside a function but am not sure how to pass the arguments to it. Here is what I’m trying to do:

void serialPrint(char* s1, char* s2){
  #ifdef DEBUG_ACTIVE
    Serial.println(s1,s2);
  #endif
}

I’m not sure what the correct syntax is … Serial.println can take one or multiple arguments if I’m not mistaken. Can anyone help me learn how to do this please.

Thanks,

2

Serial.println() only takes up to two parameters.
The two param version is meant to take a numeric type as first param and a format as second.

So you’d either do

  Serial.print(s1);
  Serial.println(s2);

Or you use Serial.printlnf("%s %s", s1, s2);

1 Like
3

If you’re just concerned with adding/removing debug code and not the syntax, try something like this. When you have DEBUG_ACTIVE defined, it will compile any debugprint() lines, otherwise they get removed from the compile.

#ifdef DEBUG_ACTIVE
#define debugprint(x) Serial.println(x)
#else
#define debugprint(x)
#endif
4

oh nice… I’ll use that.

I’m still wondering how to pass 1 or more arguments to a function (that takes one or more arguments like Serial.println) inside a function.

Like in this case:

void serialPrint(char* s1, char* s2){
  #ifdef DEBUG_ACTIVE
    Serial.println(s1,s2);
  #endif
}

I want to be able to use my functions the same way as Serial.println, eg:

serialPrint("print this line");

or

serialPrint(5, HEX);

I’m still not sure what the correct syntax is to do that. But thanks for your help.

5

Have you seen this post of mine?

The way how Serial.println() does it is via overloading which is a C++ intrinsic feature.
Have a look on the web for the ins and outs of C++.
Or if you want to do it similar to printf(), you could google for "variable argument list"

BTW: Serial.println(s1,s2); won't work as you might expect, hence my previous post.

6

Yeah, too much trouble. There’s no easy way to #define function(x, …) for variable args functions, or do overloaded syntax. You’d need to define a dbg1(x) and dbg2(x, y) or something.

7

Thanks for your help… I’ll have to google variable argument lists as you have suggested… I’m not sure how C++ handles that. Some easy saturday night reading :smile:

8

Variable args are pushed on the stack and you need special functions to access it. Look at va_start(), va_end() and vnsprintf(). vnsprintf is given a pointer to the stack like an array. One valuable resource is the Particle firmware. If you don’t know how something works, check the code. :smile:

Wow, it embeds that. Well, neat.