Where can I see the output of printf?

Question

I would like to know where I can see the output when I use the command printf. I am programming using the Arduino interface.

Update

I'll add a few lines of code for better understanding:

#include <stdio.h>
int main(void)
{
 printf("Hello World");
 return 0;
}

• letsjak: your goal is to print something out in your console of the Arduino IDE?
• letsjak: there is no main in Arduino. You have the setup for initialization and the loop for the continuing loop
• ironzionlion: @letsjak there is a main in Arduino, but it is hidden seeedstudio.com/wiki/Where_is_Main_Function

Answer 1

If you're working with the standard Arduino environment and libraries then printf() won't display anything anywhere. The reason is that microcontrollers could be connected to any number of different output/communication devices in any way. stdio would have no idea how or where to send the data.

The most common approach to outputting text from an Arduino (particularly during development) is to send it to the primary UART port using Serial.begin() and Serial.print(). If the Arduino is connected to your computer via USB then the Arduino IDE's serial monitor should display the result.

If you really want to use printf() though then it is possible to make it work (or implement similar functionality). A full explanation is on this page:

• http://playground.arduino.cc/Main/Printf

Answer 2

In setup(), start serial and choose your speed:

Serial.begin(9600);

Wherever you want to write to serial:

Serial.write("write this");

Wherever you want a newline:

Serial.println();

example

void setup() {
 // put your setup code here, to run once:
 Serial.begin(9600);
 Serial.write("Hello World");
}
void loop() {
 // put your main code here, to run repeatedly:
}

• ironzionlion: my question is actually where am I printing if I don't define Serial in void setup() and just type printf in void loop()?
• letsjak: @ironzionlion if you read the printf documentation.. you will find it...
• letsjak: @ironzionlion it's an LCD... tadaaaaaaa playground.arduino.cc/Main/Printf

Answer 3

I love old questions, and I like C (and I like printf for debugging).

There are two solutions (there are for sure more, I just mention this two):

Keep in mind the Arduino C (libraries) often does not support all escapes/formats (%f is missing)

First the "C-Style":

We just need a function, that writes a CHAR to Serial and associate this function with stdout (0)

#include <stdio.h>
char sputc(char c, FILE *) { 
 Serial.write(c);
 return c;
} 
void setup() {
 fdevopen(&sputc, 0)1; // tell stdout (0) what to use 
 
 Serial.begin(115200);
 printf("Hello World! We are here %2.2d\n",42);
 }

The other solution - my preferred one because it takes about 700 byte less, is the following:

I use vsnprintf1 and varargs1 to fill a buffer - that easy.

void say(char const* fmt, ...) {
 va_list vars;
 char buf[80]; // that is a drawback.
 va_start(vars, fmt);
 vsnprintf(buf, sizeof(buf), fmt, vars);
 Serial.print(buf);
}
void setup() {
 Serial.begin(115200);
 say("we are here %2.2d\n",10);
}

1this functions you find in internet.