Extract ints from a string

Question

I am trying to extract a few integers from a string on Arduino. I am using a Bluefruit Bluetooth module that I have linked to my mobile phone.

An application on my phone sends a string of data to the Arduino via the Bluefruit's TX/RX.

I succesfully receive the data from the application, and I can see it in my serial monitor on my computer. The strings are in this format: x:xxx,xxx,xxx with the first number being 1 to 6, and the other numbers being three 0-255.

So for example: 1:171,54,201

The string also includes a carriage return, since the next string always starts on a new line.

Can anyone help me extract these integers and set them to variables?

Answer 1

You can use the C sscanf() function:

#include <stdio.h>

char line[] = "1:171,54,201"; // read a line from Bluetooth
int num1, num2, num3, num4;

if (sscanf(line, "%d:%d,%d,%d", &num1, &num2, &num3, &num4) == 4)
{
    // use numbers as needed
}

Or the C++ wrapper, std::sscanf():

#include <cstdio>

char line[] = "1:171,54,201"; // read a line from Bluetooth
int num1, num2, num3, num4;

if (std::sscanf(line, "%d:%d,%d,%d", &num1, &num2, &num3, &num4) == 4)
{
    // use numbers as needed
}

If you have an STL available (which apparently Arduino does not), you could use the STL std::istringstream class instead:

#include <string>
#include <sstream>

std::string line = "1:171,54,201"; // read a line from Bluetooth
int num1, num2, num3, num4;

std::istringstream iss(line);
char ignore;

if (iss >> num1 >> ignore >> num2 >> ignore >> num3 >> ignore >> num4)
{
    // use numbers as needed
}

Alternatively:

#include <string>
#include <sstream>

bool readInt(std::istream &in, char delim, int &value)
{
    std::string temp;
    if (!std::getline(in, temp, delim)) return false;
    return (std::istringstream(temp) >> value);
}

std::string line = "1:171,54,201"; // read a line from Bluetooth
int num1, num2, num3, num4;

std::istringstream iss(line);

if (readInt(iss, ':', num1) && readInt(iss, ',', num2) && readInt(iss, ',', num3) && readInt(iss, '\n', num4))
{
    // use numbers as needed
}

Answer 2

With a quick google search of a similar problem, I discovered an example of how to convert a string IP address into numbers with the following code:

std::string ip ="192.168.1.54";
std::stringstream s(ip);
int a,b,c,d; //to store the 4 ints
char ch; //to temporarily store the '.'
s >> a >> ch >> b >> ch >> c >> ch >> d;

However, since your problem is "slightly" different, you could do the following:

std::string givenExample = "1:171,54,201"

//Since it is known that the value will be 1-6, just take
//the ASCII value minus 30 hex (or '0') to get the actual value.
int firstNumber = ((int)givenExample.at(0) - 0x30); //or minus '0'

givenExample.erase(0, 2); //Remove "1:" from the string

std::stringstream s(givenExample);
int secondNumber, thirdNumber, fourthNumber;
char ch;
s >> secondNumber >> ch >> thirdNumber >> ch >> fourthNumber;

However, if you compare the first example to the second, the ip string is in almost the same format as your example: 4 ints separated by chars. So both will work, depending on which one makes more sense to you.

As far as how you are going to be reading that data in (Dealing with the carriage return), that depends on your interface to the serial data stream received from Arduino.