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)

• Majenko: Does this help? majenko.co.uk/blog/splitting-text-c
• chrisl: I recommend learning how to use the strtok() function. It is also described in Majenkos blog entry

Answer 1

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(){}

Answer 2

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.
}

• Juraj: but the code for scanf takes 1.5kB flash memory