How include #defined constants in Serial.print or Serial.println?

Projects Programming
1

Hello, is it possible to include constants (defined with #define) in the Serial.print or Serial.println function? If so, how would this be done?

I was looking at "stringification" in C++, and it seems to indicate you can include the defined constant name prepended with a # (hash) symbol as in the following example:
(https://gcc.gnu.org/onlinedocs/cpp/Stringification.html)

#define WARN_IF(EXP) \
     do { if (EXP) \
             fprintf (stderr, "Warning: " #EXP "\n"); } \
     while (0)
     WARN_IF (x == 0);
          ==> do { if (x == 0)
                fprintf (stderr, "Warning: " "x == 0" "\n"); } while (0);

But when I try to include the constant in this way, the Arduino compiler complains of stray # symbol.

For example:

#define THEVALUE hello123
Serial.println("This is the value: " #THEVALUE);

But the compiler doesn't replace the value within strings, so this doesn't work either:

#define THEVALUE hello123
Serial.println("This is the value: #THEVALUE");

Thanks for any insight!

3

Fist of all, why not make it a normal C++ constant?

const char TheValue[] = "hello123";

Serial.println(TheValue);

If you really want it from a preprocessor define, you can do

#define MYVALUE "hello123"

Serial.println(MYVALUE);

Or if it's really a problem to make the #define as a string you can use the double define trick:

#define THEVALUE hello123

#define STRINGIFY(x) #x
#define TOSTRING(x) STRINGIFY(x)

Serial.println(TOSTRING(THEVALUE));
5

STRINGIFY(THEVALUE) expands to "THEVALUE"

TOSTRING(THEVALUE) expands to STRINGIFY(hello123) which expands to "hello123"

6

These work except in my use-case where the defined value includes commas (it's an array).
(I'm using this to define the IP address for the ethernet module, and since Ethernet.begin requires a byte array for the IP address, I'm defining the IP as #define IP_ADDRESS 192,168,1,100.

Then I want to display it on the serial console so I don't have to depend on a piece of paper taped to the outside of the unit to keep track of the IP address.

For example, this fails:

#define MYVAL 123,456
#define st(a) #a
#define xst(a) st(a)

Serial.print(xst(MYVAL));

Yields an error: the macro expected 1 parameter but got 2

7 
#define MYVAL (123,456)
#define st(a) #a
#define xst(a) st(a)

void setup()
{
  Serial.begin(115200);
  Serial.print(xst(MYVAL));
}

void loop()
{
}

Prints (123,456). The parens may, or may not, be a problem.