number of elements in a char array?

Projects Programming
1

Okay so i am trying to make a menu on a 4x20 LCD screen. On the top of the screen i would like to be able to tell the user what level he is on. To do this i will need the number of elements of the char array, which would correspond to the line. I could of course add the number manually, but that would be annoying when adding sub menues etc.

so far i have tried these options i could find through a search and none of them seems to work.

strLength = strlen(GUI);                 // ERROR!
strLength = sizeof(GUI)/sizeof(int);          // strLength =1!
strLength = sizeof(GUI)/sizeof(GUI[0]);    // strLength =1!

Here are my whole code. As you can see i would like it to give me the answer of 5 elements!

/* Written by Kristoffer P. Sminge 2014*/

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <string>
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  // Set the LCD I2C address



char* mainMenu[] = {
  "Main Menu", "Seperation", "Options", "Manual Move", "Statisticks"};


void setup()   /*----( SETUP: RUNS ONCE )----*/
{
  Serial.begin(9600);
  lcd.begin(20,4);

}
void loop()   /*----( LOOP: RUNS CONSTANTLY )----*/
{
  navLCD(mainMenu);
  delay(10000);
}

void navLCD(char* GUI[]){
   int cursor=1;
   int strLength;
   
   strLength = strlen(GUI);
   
   Serial.print(strLength);
   lcd.print("__________________/_");
   lcd.setCursor(3,0);
   lcd.print(GUI[0]);
   lcd.setCursor(17,0);
   lcd.print(cursor); 
   lcd.setCursor(19,0);
   lcd.print(strLength);
   
  for (int i = 1; i < 4; i++){
    lcd.setCursor(0,i);
    lcd.print(GUI[i]);
    delay(500);
  }
}

Anyone have an idea?

2

Hi you get 1 as length because GUI is a pointer in your code and not an array. Hope this cab help you.

3

Okay i think i get what you are saying. But how do i then find the number of elements in my function? At this point i am using the main menu, but later i would like the same routine to be able to write my sub-menue's, when calle from my main loop.

4

But how do i then find the number of elements in my function?

You don't, unless there is something in the array that defines the end of the array, as the NULL in a NULL-terminated array of chars does. You need to pass the size to the function.

5

Sorry for being a bit of a newb here, but how do i NULL terminate my array?

I guess that then i would make a for-loop increment by one, until i hit the NULL value?

as said i am trying to make a menu system, do you guess think that i am on the right track or is there an easier way?

6

but how do i NULL terminate my array?

Which array? The array of pointers? The one called maniMneu? Or the one called GUI (in the function)?

I guess that then i would make a for-loop increment by one, until i hit the NULL value?

Yes.

am on the right track or is there an easier way?

Pass the number of items in the menu into the function.

7

Thank you for you guys for quick replies and sorry for being such a noob :slight_smile:

I would rather avoid having to send the length of the array every time i call my function. It seems that i would have to do it a lot of times, but maybe i am not seeing the big picture?

Okay so i think i have null terminated my arrays:

char* mainMenu[] = {
  "Main Menu", "Seperation", "Options", "Manual Move", "Statisticks", '\0'};

In my GUI function i now run this loop

  for (int a = 1; a < 20; a++){
    if(GUI[a] != "\0"){
      ++strLength;
    }
    else
      break    
  }

It will not compile, and if it could i am not sure it will work.

Here are the whole code, in case the parts did not make sense!

/* Written by Kristoffer P. Sminge 2014*/

#include <Wire.h>
#include <LiquidCrystal_I2C.h>
#include <string>
LiquidCrystal_I2C lcd(0x27, 2, 1, 0, 4, 5, 6, 7, 3, POSITIVE);  // Set the LCD I2C address



char* mainMenu[] = {
  "Main Menu", "Seperation", "Options", "Manual Move", "Statisticks", '\0'};


void setup()   /*----( SETUP: RUNS ONCE )----*/
{
  Serial.begin(9600);
  lcd.begin(20,4);

}
void loop()   /*----( LOOP: RUNS CONSTANTLY )----*/
{
  navLCD(mainMenu);
  delay(10000);
}

void navLCD(char* GUI[]){
  int cursor=1;
  int strLength;

  for (int a = 1; a < 20; a++){
    if(GUI[a] != "\0"){
      ++strLength;
    }
    else
      break    
  }

  Serial.print(strLength);

  lcd.print("__________________/_");
  lcd.setCursor(3,0);
  lcd.print(GUI[0]);
  lcd.setCursor(17,0);
  lcd.print(cursor); 
  lcd.setCursor(19,0);
  lcd.print(strLength);

  for (int i = 1; i < 4; i++){
    lcd.setCursor(0,i);
    lcd.print(GUI[i]);
    delay(500);
  }
}
8

It seems that i would have to do it a lot of times, but maybe i am not seeing the big picture?

But the size shouldn't change.

'\0' is a NULL character. That's different from a NULL pointer.

    if(GUI[a] != "\0"){

Should simply be

    if(GUI[a])

      break

That didn't even compile, did it?

9

If you want to know how long the string is, you need strlen( GUI[0] ), strlen( GUI[1] ) etc.

GUI itself is an array of 5 pointers to char, not any number of char.

10

No it did not... but now it does :slight_smile: Thank you so much for your help :smiley:

i have this code now:

  int strLength=0;

  for (int i = 1; i < 20; i++){
    if(GUI[i]){
      ++strLength;
    }
    else{
      break;    
    }
  }

First i did not set strLength = 0, an i got some strange high value results. Is that because C++ just puts in a random number?

You are right that the length does not change. But i like my code to be as modular as possible, and maybe one day i will need the possibility to add menus in program, thus it will be nice to not have to count the number of elements :slight_smile:

11 
for (int i = 1; i < 20; i++)

Just use strlen - it won't make the mistake of ignoring the first character.

12

ohh... one follow up question:

In the code above i have just made my for-statement with 20 iterations. I guess that i might as well put this to an infinite high number, since i put in a break in the loop.

Is there a best practice to do this? Or should i avoid infinity?

13

Just use strlen - it won't make the mistake of ignoring the first character.

OP can't use strlen(), because GUI isn't a string. It's an array of pointers, the last one of which is NULL.

OP does need to change the initial value of the loop to 0.

In the code above i have just made my for-statement with 20 iterations. I guess that i might as well put this to an infinite high number, since i put in a break in the loop.

You should use a while loop instead. No need to define an upper limit.

14

AWOL:

for (int i = 1; i < 20; i++)

Just use strlen - it won't make the mistake of ignoring the first character.

I did try using strlen but because it is a function that points to my array, this does not work (if i understood the first answer correctly?).

I start the iteration at 1 because the first element defines my headline for my display, so i don't want this to count as an option. Else, it was well spottet :slight_smile:

15

PaulS:
You should use a while loop instead. No need to define an upper limit.

How would i use a while loop? How would i increment i-variable to get it to loop through all of my array?

16

How would i use a while loop? How would i increment i-variable to get it to loop through all of my array?

int i = 0;
while(GUI[i])
{
   i++;
}
// At this point, i is the number of items in the array.
17

Of course :roll_eyes:

Thank you so much PoulS