Converting String to number (int, long...)

Projects Programming
1

I was looking on the forum as I was struggling with this question, and only found answers that were not satisfactory to me... Since that was an old post without ability to reply, here is my post and how I solved the problem:

First, reading data from serial, to build a String object

if (mySerial.available()) {
            command ="";
            while(mySerial.available())
            {
              command += (char)mySerial.read();
            }

Then getting the number out of the string (here I have an integer number which I know is 4 characters long:

char delaystr[5]; //create the char array
command.toCharArray(delaystr,5); //convert the String 'command' into the char array
int delayT = atoi(delaytstr); //convert the char array into integer

Voila!

2

Or better yet, get rid of the String objects altogether!

3

This is simplified code, but I use the String object to split the string and do other things with it... If the 'string' received is all you need to convert, then sure you can get rid of it entirely and just use atoi()

4

elarduino:
This is simplified code, but I use the String object to split the string and do other things with it... If the 'string' received is all you need to convert, then sure you can get rid of it entirely and just use atoi()

Everything done with the String object can be done using the normal c-style strings without the memory hassles that you run into.

5

Everything done with the String object can be done using the normal c-style strings without the memory hassles that you run into.

But not nearly as easy.

6

zoomkat:
But not nearly as easy.

Ya, It's much easier to try and debug your code down the road when you run into memory errors and end up having to re-write using c-style strings anyway...

I see Strings the same way I see delay(): As the complexity of your code goes up, the likelihood that you'll run into issues to the point where you'll have to re-write the code to use c-style strings/millis() also increases.

So I am not saying never use these, but if you don't want to learn the alternative ways that are more scalable, don't try and write any complex sketches.

7

elarduino:
I was looking on the forum as I was struggling with this question, and only found answers that were not satisfactory to me... Since that was an old post without ability to reply, here is my post and how I solved the problem:

First, reading data from serial, to build a String object

if (mySerial.available()) {

command ="";
            while(mySerial.available())
            {
              command += (char)mySerial.read();
            }




Then getting the number out of the string (here I have an integer number which I know is 4 characters long:

char delaystr[5]; //create the char array
command.toCharArray(delaystr,5); //convert the String 'command' into the char array
int delayT = atoi(delaytstr); //convert the char array into integer




Voila!

For what it's worth, here is how I get user input from the serial terminal (text or numeric):

First, the basic "line input" code:

// read a line from user into buffer, return char count
int readline(char *buf, int limit)
{
        int x;
        int ptr = 0;

        while(1) {

                if(Serial.available()) {

                        x = Serial.read();

                        if(x == 0x0D) {  // cr == end of line
                                buf[ptr] = 0; // null terminate string
                                return ptr; // return char count
                        }

                        if(x == 0x08) {  // backspace
                                if(ptr > 0) {
                                        ptr--;
                                        buf[ptr] = 0;
                                        Serial.print((char) 0x08); // backup cursor
                                        Serial.print((char) 0x20); // erase char
                                        Serial.print((char) 0x08); // backup cursor

                                } else {
                                        Serial.print((char) 0x07); // beep == home limit
                                }

                        } else {
                                if(ptr < (limit - 1)) {
                                        Serial.print((char) x);
                                        buf[ptr] = x;
                                        ptr++;

                                } else {
                                        Serial.print((char) 0x07); // beep == end limit
                                }
                        }
                }
        }
}

You provide a buffer (i.e. "char buffer[32]"), then call the readline code with "buffer" and a limit as to how many characters to accept (of course, no more than the buffer size!).

If you want a numeric value from the user, then just do this:

// get user input, return as a float value
float get_user_input(void)
{
        readline(buffer, 8); // buffer is 256 bytes, but we only allow 8 here which is enough
        return atof(buffer);
}

Lastly, if you want to look for text data (such as "Y" or "N" for yes or no), you may want to stick an extra bit of code in there to keep the character case constant (i.e. convert all a-z to A-Z) so you only have to test for uppercase.

Hope this helps.