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Topic: query on read and write data using sd card (Read 787 times) previous topic - next topic

amzar89

Mar 28, 2014, 08:31 pm Last Edit: Mar 28, 2014, 08:34 pm by amzar89 Reason: 1
basically we can read and write data in text file using sd card by implement code below and only can access one text file at a time

   
Code: [Select]
*/

#include <SD.h>

File myFile;

void setup()
{
// Open serial communications and wait for port to open:
 Serial.begin(9600);
  while (!Serial) {
   ; // wait for serial port to connect. Needed for Leonardo only
 }


 Serial.print("Initializing SD card...");
 // On the Ethernet Shield, CS is pin 4. It's set as an output by default.
 // Note that even if it's not used as the CS pin, the hardware SS pin
 // (10 on most Arduino boards, 53 on the Mega) must be left as an output
 // or the SD library functions will not work.
  pinMode(10, OUTPUT);
 
 if (!SD.begin(4)) {
   Serial.println("initialization failed!");
   return;
 }
 Serial.println("initialization done.");
 
 // open the file. note that only one file can be open at a time,
 // so you have to close this one before opening another.
 myFile = SD.open("test.txt", FILE_WRITE);
 
 // if the file opened okay, write to it:
 if (myFile) {
   Serial.print("Writing to test.txt...");
   myFile.println("testing 1, 2, 3.");
   // close the file:
   myFile.close();
   Serial.println("done.");
 } else {
   // if the file didn't open, print an error:
   Serial.println("error opening test.txt");
 }
 
 // re-open the file for reading:
 myFile = SD.open("test.txt");
 if (myFile) {
   Serial.println("test.txt:");
   
   // read from the file until there's nothing else in it:
   while (myFile.available()) {
       Serial.write(myFile.read());
   }
   // close the file:
   myFile.close();
 } else {
   // if the file didn't open, print an error:
   Serial.println("error opening test.txt");
 }
}

void loop()
{
   // nothing happens after setup
}


is it possible to access the data in a two text files simultaneously in a time?

PaulS

Quote
and only can access one text file at a time

Depends on which SD library you are using.

Quote
is it possible to access the data in a two text files simultaneously in a time?

Each will require a 512 byte buffer. For 2 files on a UNO, that's half the memory.

The Arduino is not ideally suited as a file storage device. What are you trying to do that requires multiple files open at a time?

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