Help creating alphanumeric string

[eh_asuna]

Hello, I have a couple questions revolving creating a random alphanumeric string in arduino.

1st- Is this similar to creating it in C++?
2nd- How exactly would I go about it using an arduino leonardo because I want to be able to use a function to generate it multiple times instead of rewriting code everytime and or only being able to use it once.

Essentially with my arduino leonardo I have the ability to
Keyboard.printIn()
and I want to be able to run something like
Keyboard.printIn(randomString());
and then have it write that out.

If anyone can help I'd appreciate it a lot.

[psousalima]

1. Yes. Quite similar.
2. Well that is exactly what functions are for, that shouldn't change your code nor increase the code complexity.

There was previously Generate random alphanumeric on this forum, I believe this was not the only post on it aswell.

In the end

[eh_asuna]

Thank you, I just read through it and I am confused since when writing to my arduino leonardo I am only using the void setup part. And the code in that post uses the void loop and setup so how would I even implement that into my code?

[sterretje]

@eh_asuna

I am only using the void setup part

Any reason why?

You can move the full content of loop() into setup().

You can also run loop() once if so inclined.

void loop()
{
  // do some stuff here
  ...
  ...

  // hang forever
  for(;;);
}

[eh_asuna]

I just need help making the function to randomly generate an alphaNumerical string.
This is what I have so far but it's not working
void randStr(int lengt){
String randString;
int randN;
for(int x; x < lengt; x++){
randN = rand(97, 122);
randString = randString + to_string(randN);
randN = rand(0, 9);
randString = randString + to_string(randN);
}
}

[GoForSmoke]

Microcontrollers have little RAM.
You will do better using C char-array zero-terminated strings than C++ String objects.
Avoid dynamic allocation like the plague.

Use Serial to communicate with Serial Monitor.

Arduino Foundations -- one page of docs on the Main Arduino site.

[sterretje]

@eh_asuna, please edit your post, select all code and click the </> button to apply so-called code tags and next save your post. It makes it easier to read, easier to copy and prevents the forum software from incorrect interpretation of the code.

@eh_asuna

but it's not working

Please explain. And without context (the complete program) we have no idea what can be wrong.

[330R]

@eh_asuna I suggest that you break your problem into sub-problems and work out each of one them separately. For instance: can you generate a random string by itself? Can you output a constant string by itself?

I agree with the advice to avoid String objects and use vanilla char arrays instead.

[killzone_kid]

@eh_asuna

randString = randString + to_string(randN);

You assigned result to local variable, ok, and then what?

[nicolajna]

You can do something like this

#include <stdlib.h>

static const char alphanumericCharacters[] = {
    '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f', 'g', 'h,', 'i', 'j', 'k', 'l',
    'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v', 'w', 'x', 'y', 'z', 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H',
    'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z'
};

static void randomString(char *str, unsigned int count) {

    unsigned int i;
    for (i = 0; i < count; i++) {
        str[i] = alphanumericCharacters[rand() % sizeof(alphanumericCharacters)];
    }

    str[i] = '\0';
}

int main() {

    char str[129];
    randomString(str, 128);

    return 0;
}

I don't have an Arduino at hand right now, so this is written in plain C but should be easily adaptable.

[Whandall]

@eh_asuna

randN = rand(0, 9);
randString = randString + to_string(randN);

This will not add numbers in ASCII to the string, but control characters,
including the "end of cstring" character '\0'.

[GoForSmoke]

  char chr;

// ............ snip

// ............ somewhere in void loop ---- How to filter data to handle by type

  if (( chr >= '0' ) && ( chr <= '9' )  { chr is a text digit, value = chr - '0';  do something; }

  else   if (( chr >= 'A' ) && ( chr <= 'Z' )  { chr is text uppercase alpha;  do something; }
  
  else   if (( chr >= 'a' ) && ( chr <= 'z' )  { chr is text lowercase alpha;  do something; }

  else  chr = 0;  // not an alpha-numeric

you could do

  for ( chr = '0'; chr < ( '9' + 1 ); chr++ )  { print( chr ); }
  print( "\n\n" );

  for ( chr = 'A'; chr < ( 'Z' + 1 ); chr++ )  { print( chr ); }
  print( "\n\n" );

  for ( chr = 'a'; chr < ( 'z' + 1 ); chr++ )  { print( chr ); }
  print( "\n\n" );