Reading data from sd card with specified extension

Projects Programming
1

Hello, I want to read a specific string from several other that are in a file inside the sd card. My data format is such that each data is written in a separate line and has its own extension :

D1|test N1
D2|test N2
D3|test N3
D4|test N4
D5|test N5
D6|test N6
D7|test N7

I want to read the data in D5
My output should look like this:

test N5
2

What have you tried ?

For instance, can you open the file, read it and print the line of data ?

3

yes, I understand the library example itself but I can't extract a particular data from other data

4

I would read the whole of each line into a C style string (a zero terminated array of chars) then test whether the first 2 characters match what you are looking for and, if so, print the rest of the string

5

Let's do one more thing, how can I read a specific line from among other lines? (end of line has \n)

6

I want to try to look for the index character, then read the characters after it until the end of the line, I have no idea how to move the cursor after the index character:

  while (Serial.available() > 0) {
    char input = Serial.read();

    if (input == 'S') {
      String myinput = Serial.readStringUntil('\n');

      if (SD.exists("data.txt")) {
        Serial.println("data.txt exists.");
        myFile = SD.open("data.txt");
        
        **if (myFile.find(myinput)) {**
          
        **}**
      } else {
        Serial.println("data.txt doesn't exist.");
        myFile = SD.open("data.txt", FILE_WRITE);
        myFile.close();
      }
    }
  }
7

Possible ONLY if all lines are the same length. If so, you can compute the position of the line in your file and use "seek" to position at that spot.

8

Could you write an example?

9

Start with something like this

#include <SD.h>
#include <SPI.h>

File file;
char line[100];

void setup()
{
  Serial.begin(115200);
  if (!SD.begin(4))
  {
    Serial.println(F("begin error"));
    while (1);
  }
  Serial.println(F("begin success"));
  readFile();
}

void loop()
{
}

boolean readLine()
{
  byte index = 0;
  while (file.available())
  {
    char inChar = file.read();
    if (inChar == '\n')
    {
      return false;
    }
    else
    {
      line[index++] = inChar;
      line[index] = '\0';
    }
  }
  return true;
}

void readFile()
{
  file = SD.open("test.txt", FILE_READ);
  if (!file)
  {
    Serial.println(F("error opening file"));
    while (1);
  }
  if (file)
  {
    Serial.println(F("open success"));
    boolean finished = false;
    while (!finished)
    {
      finished = readLine();
      Serial.println(line);
    }
    file.close();
  }
}

The line of data will be in the line string and can be parsed using the strtok() function

10

Can you search for examples of using "seek"?

11

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