arduino_printf.cpp

#include <Arduino.h>

int getChar(FILE *fp) {
    while (!(Serial.available()))
        ;
    return (Serial.read());
}

int putChar(char c, FILE *fp) {
    if (c == '\n') {
        putChar((char)'\r', fp);
    }
    Serial.write(c);
    return 0;
}

void setup() {
    Serial.begin(9600);
    fdevopen(putChar, getChar);
    printf("Hello %s!", "there")
}