How do I print multiple variables in a string?

I wouldn't normally put two answers to a question, but I only just found this today, where you can use printf without any buffer.

// Function that printf and related will use to print
int serial_putchar(char c, FILE* f) {
    if (c == '\n') serial_putchar('\r', f);
    return Serial.write(c) == 1? 0 : 1;
}

FILE serial_stdout;

void setup(){
    Serial.begin(9600);

    // Set up stdout
    fdev_setup_stream(&serial_stdout, serial_putchar, NULL, _FDEV_SETUP_WRITE);
    stdout = &serial_stdout;

    printf("My favorite number is %6d!\n", 12);
}

void loop() {
  static long counter = 0;
  if (millis()%300==0){
    printf("millis(): %ld\tcounter: %ld (%02X)\n", millis(), counter, counter++);
    delay(1);    
  }
}

This still has the floating point limitation.

edit: I thought I would do a little testing on this, and it works quite well. I added a better test to the loop with formatted output.

This is probably not better, just different. You can use the String object for output. These objects allow concatenation and support automatic typecasting.

Serial.begin(9600);
String label = "Var";
const byte nValues = 3;
int var[nValues] = {36, 72, 49};

for (int i = 0; i < nValues; i++) {
    String stuff = label + i + ": ";
    Serial.println(stuff + var[i]);
}

I usually used Tabs to make things line up better in the Serial. Having things line up like I do allow the arduino to fire as fast as possible while being able to notice certain changes in the variables.

Try something like this:

Serial.println("Var 1:\tVar 2tVar 3:");
Serial.print("\t");
Serial.print(var1);
Serial.print("\t");
Serial.print(var2);
Serial.print("\t");
Serial.print(var3);
Serial.println();

Or something like this:

Serial.print("Var 1:");Serial.println(var1);
Serial.print("\tVar 2:");Serial.println(var2);
Serial.print("\tVar 3:");Serial.println(var3);

I usually (painfully) stick with multiple lines of Serial.print but when it becomes convoluted I go back to sprintf. It's annoying in that you have to have an available buffer for it.

Usage is as simple (??) as:

char buffer[35]; // you have to be aware of how long your data can be
                 // not forgetting unprintable and null term chars
sprintf(buffer,"var1:%i\tvar2:%i\tvar3:%i",var1,var2,var3);
Serial.println(buffer);

A word of warning though, it doesn't (by default) support floating types.

Using Streaming.h, in place of

Serial.print("Var 1:");Serial.println(var1);
Serial.print(" Var 2:");Serial.println(var2);
Serial.print(" Var 3:");Serial.println(var3);

one can write

Serial << "Var 1:" << var1) << " Var 2:" << var2 << " Var 3:" << var3 << endl;

The definition of << in Streaming.h in effect translates that into a series of ordinary Serial.print() calls. That is, << is syntactic sugar, implemented without increasing code size.

If you don't have Streaming.h installed, get Streaming5.zip from arduiniana.org. Unzip it in your libraries directory, for example in ~/sketchbook/libraries. Add the line #include <Streaming.h> within sketches where you use << as a stream operator.

Base-conversion specifiers _HEX, _DEC, _OCT, and _BIN are provided, as well as a _FLOAT function (with number of decimal places) and endl. For example, to print latitude and longitude values in a form like "Your coordinates are -23.123, 135.4567” one could write:

Serial << "Your coordinates are " << _FLOAT(latitude,3) << ", " << _FLOAT(longitude,4) << endl;

This could also be written as

Serial << F("Your coordinates are ") << _FLOAT(latitude,3) << ", " << _FLOAT(longitude,4) << endl;

which would keep the longer string in PROGMEM instead of bringing it into RAM.

Note, Streaming.h doesn't build any strings as such; it just delivers the text of its <<-arguments to a stream. A PString class at arduiniana can build strings from stream inputs, if strings instead of streamed output are desired or needed.

From http://playground.arduino.cc/Main/Printf I observed this is working fine on my mega2560

That's all it just worked, no need for vsnprintf_P or PROGMEM ...

#include "Arduino.h"
void local_printf(const char *format, ...)
{
static char line[80];
va_list args;
va_start(args, format);
int len = vsnprintf(line, sizeof(line), format, args);
va_end(args);
for (char *p = &line[0]; *p; p++) {
    if (*p == '\n') {
        Serial.write('\r');
    }
    Serial.write(*p);
}
if (len >= sizeof(line))
    Serial.write('$');
}

void setup()
{
Serial.begin(115200);
local_printf("%s:%d: %s\n", __FILE__, __LINE__, __PRETTY_FUNCTION__);
}

void loop()
{
static int count=0;
local_printf("%s:%d: %s %d\n", __FILE__, __LINE__, __PRETTY_FUNCTION__, count++);
delay(1*1000);
}

// src/main.c:24: void setup()
// src/main.c:30: void loop() 0
// src/main.c:30: void loop() 1