Using std::cin with the ESP32

Projects Programming
1

I'm trying to use std::cin and std::cout with the ESP32. cout seems to work fairly well, but whenever I try to use cin for user input, it just seems to time-out immediately, without updating the variable I'm trying to cin to.

Here's a fairly simple program that illustrates my problem. (This is Listing 2.6 in the book "Sams Teach Yourself C++ in One Hour a Day", 9th edition - but modified for the Arduino setup() & loop() structure.)

#include <iostream>
#include <string>
using namespace std;

void setup() {
  Serial.begin(115200);
  Serial.setTimeout(LONG_MAX);  // Wait for input essentially forever

  // Declare a variable to store an integer
  int inputNumber;

  cout << "Enter an integer:  ";

  // store integer given user input
  cin >> inputNumber;

  // The same with text i.e. string data
  cout << "Enter your name:  ";
  string inputName;
  cin >> inputName;

  cout << inputName << " entered " << inputNumber << endl;
}

void loop() {
}

The code compiles fine, but when I run it, the following appears on the Serial Monitor, with no time for me to enter anything.

Enter an integer:  Enter your name:   entered 0

I know there is a library ArduinoSTL, but it doesn't support the ESP32.

Thanks for any help,

A.J.

2

I suspect that 'cin' has a timeout, like Serial.parseInt() or Serial.readString(). Does the library give you a way of knowing if there is data in the input buffer (like Serial.available())?

3

Thanks for responding.

In a "normal" implementation (like running on a PC with keyboard and screen), I don't think there's any timeout, although, it sure seems like there might be a need for one. But since cin and cout are connected to Serial in the Arduino implementation, I agree with you that there seems like there would be a timeout, that's why I have a Serial.setTimeout(LONG_MAX); call at the beginning of setup().

Where should I look in the library for information about a timeout or input buffering? I assume you're telling me to look in iostream, but how do I do that?

A.J.

4

I have no idea. I found the 'iostream' file and it creates eternal references for 'cin'. 'cout', 'cerr', and 'clog'. I expect the C++ Runtime Library is not dependent on the Arduino library o it ha nothing to do with 'Serial'. Probably based on some I/O driver for the OS.

I'm just guessing might be causing the symptoms you see.

5

cin is not tied to Serial.
You'll need to use the facilities provided with Serial.

6

What is the use of cin?

7

For Arduino, there really isn't one.
cin is for programs that run in the shell, console, or command prompt on your computer.
The programming language for Arduino is a slightly enhanced/simplified version of C++, and C++ has many applications beyond Arduino. There are a few things in C++ that don't work on Arduino.
There's a lot more too it but that's a simplified way to say it.

8

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