Arduino Serial output C macros

Here is a quickie.

In Arduino, instead of being able to use things like printf() and puchar(), console output is done by using the Serial library routines. It provides functions such as:


These do not handle any character formatting like printf() does, but they can print strings, characters or numeric values in different formats. Where you might do something like:

int answer = 42;
printf("The answer is %d\r\n", answer);

…the Arduino version would need to be:

int answer = 42;
Serial.print("This answer is ");

To handle printf-style formatting, you can us sprintf() to write the formatted string to a buffer, then use Serial.print() to output that. I found this blog post describing it.

I recently began porting my Arduino Telnet routine over to standard C to use on some PIC24 hardware I have at work. I decided I should revisit my Telnet code and try to make it portable, so the code could be built for Arduino or standard C. This would mean abstracting all console output, since printf() is not used on the Arduino.

I quickly came up with these Arduino-named macros I could use on C:

#include <stdio.h>
#include <stdlib.h>

#define SERIAL_PRINT(s)     printf(s)
#define SERIAL_PRINTLN(s)   printf(s"\r\n")
#define SERIAL_WRITE(c)     putchar(c)

int main()
    SERIAL_PRINT("1. This is a line");

    SERIAL_PRINTLN("2. This is a second line.");

    SERIAL_PRINT("3. This is a character:");


    return EXIT_SUCCESS;

Ignoring the Serial.begin() setup code that Arduino requires, this would let me replace console output in the program with these macros. For C, it would use the macros as defined above. For Arduino, it would be something like…

#define SERIAL_PRINT(s)     Serial.print(s)
#define SERIAL_PRINTLN(s)   Serial.println(s)
#define SERIAL_WRITE(c)     Serial.write(c)

By using output macros like that, my code would still look familiar to Arduino folks, but build on a standard C environment (for the most part).

This isn’t the most efficient way to do it, since Arduino code like this…


…would be one printf() in C:

printf ("[%d]\n", val);

But, if I wanted to keep code portable, C can certainly do three separate printf()s to do the same output as Arduino, so we code for the lowest level output.

One thing I don’t do, yet, is handle porting things like:

Serial.print(val, HEX);

On Arduino, that outputs the val variable in HEX. I’m not quite sure how I’d make a portable macro for that, unless I did something like:

#define SERIAL_PRINT_HEX(v) Serial.print(v, HEX)

#define SERIAL_PRINT_HEX(v) printf("%x, v)

That would let me do:


I expect to add more macros as-needed when I port code over. This may be less efficient, but it’s easier to make Arduino-style console output code work on C than the other way around.


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