Would someone provide an example of extracting data from a char array?

Question

I have tried so many things now that I am just confused.
I am not understanding the way char arrays work.
I can't get the date and names extracted. And when I use just strings, I jam up the memory.

Below was my last attempt, before asking the question.

while (f.available()) {
  String line = f.readStringUntil('\n');

  if (line.startsWith("04-23")) {
    currentDay = 1;
    int str_len = line.length() + 1;
    char char_array[str_len];
    line.toCharArray(char_array, str_len);
    Serial.println(char_array);                 // Everything works to here
    for (int j = 0; j < 2; j++) {
      b += char_array[j];
    }
    bMth = b.toInt (); // This should be an int of the birth month in this case: 04
  }
}

Var:
format: MM-DD-YYYY,Name  // this is inside the file
line = "04-23-2020,James"  // This is the output from - Serial.println(char_array);

What I am trying to do is

Extract the month/day so that I can compare it to today.
The year so I can calculate the age.
The name to display on OLED.
Everything else seems to work, but I can't get my head wrapped around the char array access.

To do this in PowerShell I would do:

$line = "04-23-2020,James"

$dob = ($line.Split(","))[0]
$bMth = ($dob.Split("-"))[0] # This is not used in this example
$bDy = ($dob.Split("-"))[1]  # This is not used in this example
$bYr = ($dob.Split("-"))[2]

$age = $(get-date -UFormat %Y) - $bYr

Clear-Host
Write-Host (@'
Name: {0}
Age:  {1}

'@ -f $($line.Split(","))[1], $age)

In Python:

import datetime as dt

line = "04-23-2020,James"

dob = (line.split(',')[0])
bMth = (dob.split("-"))[0] # This is not used in this example
bDy = (dob.split("-"))[1]  # This is not used in this example
bYr = (dob.split("-"))[2]

age = int(dt.datetime.now().year) - int(bYr)

print('Name: ',(line.split(',')[1]))
print('Age: ', age)

I recommend learning how to use the strtok() function. It is also described in Majenkos blog entry — chrisl
– chrisl, Commented Apr 26, 2021 at 21:50

VE7JRO · Accepted Answer · 2021-04-26 23:55:45Z

When working with Arduino, cplusplus.com is your friend. Scroll down and look on the left side under (string.h). Lot's of great char functions there. Other useful functions such as iota() - cplusplus.com.

Here's one way to accomplish the parsing of the input data.

// Sketch uses 2064 bytes (6%) of program storage space.
// Global variables use 323 bytes (15%) of dynamic memory.
// Arduino IDE 1.8.9.
char line[] = "04-23-2020,James";
char Name[100];
unsigned int Month, Day, Year;

// Make an attempt to validate the input data.
byte Counter = 0;

void setup(){

  Serial.begin(9600);

  char * pch = strtok(line, "-,");

  while(pch != NULL){
    if(Counter == 0){Month = atoi(pch);}
    else if(Counter == 1){Day = atoi(pch);}
    else if(Counter == 2){Year = atoi(pch);}
    else if(Counter == 3){strcpy(Name, pch);}
    pch = strtok(NULL, "-,");
    Counter += 1;
  }

  // Print out the data.
  if(Counter == 4){
    Serial.println(Month);
    Serial.println(Day);
    Serial.println(Year);
    Serial.println(Name);
  }
  else{
    Serial.println("Error");
  }

}

void loop(){}

tim · Accepted Answer · 2021-04-26 22:03:32Z

0

You could try sscanf if your data format is fixed, something like this:

char line[] = "04-23-2020,James";
int day, month, year;
char name[100];
if (sscanf(line, "%d-%d-%d,%s", &month, &day, &year, name) == 4)
{
    // Process the four items.
}

answered Apr 26, 2021 at 22:03

tim

6996 silver badges15 bronze badges

1

but the code for scanf takes 1.5kB flash memory

Juraj
– Juraj ♦

2021-04-27 04:57:25 +00:00
Commented Apr 27, 2021 at 4:57

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