user30063: it's possible to read value from a file inside sd card?
I'm trying to start with the sample code 
/*
  SD card read/write

 This example shows how to read and write data to and from an SD card file
 The circuit:
 * SD card attached to SPI bus as follows:
 ** MOSI - pin 11
 ** MISO - pin 12
 ** CLK - pin 13
 ** CS - pin 4

 created   Nov 2010
 by David A. Mellis
 modified 9 Apr 2012
 by Tom Igoe

 This example code is in the public domain.

 */

#include <SPI.h>
#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 native USB port only
  }


  Serial.print("Initializing SD card...");

  if (!SD.begin(53)) {
    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("testing1 1, 2, 3.");
    myFile.println("testing2 1, 2, 3.");
    myFile.println("testing3 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
}

but here he read all the contnent of the file, i want to read only testing 3 part . Thank's for help 

user30063: i found this solution with use of strcmp:
when i read the file i compare the result str coming from file flux
/*
 SD card read/write

This example shows how to read and write data to and from an SD card file   
The circuit:
* SD card attached to SPI bus as follows:
** MOSI - pin 11
** MISO - pin 12
** CLK - pin 13
** CS - pin 4

created   Nov 2010
by David A. Mellis
modified 9 Apr 2012
by Tom Igoe

This example code is in the public domain.

*/

#include <SD.h>

File myFile;
char buf[10];

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(53)) {
   Serial.println("initialization failed!");
   return;
 }
 Serial.println("initialization done.");  

 // 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()) {
      myFile.read(buf,2);       
       if(strncmp(buf, "12", 2) == 0)//for lenght i use 2 becouse im looking for a number with 2 digit
       {
           Serial.println("Match!");
           }
          break;     
       }
   }
   // 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
}


30063: <p>it's possible to read value from a file inside sd card?</p>

<p>I'm trying to start with the sample code </p>

<pre><code>/*
  SD card read/write

 This example shows how to read and write data to and from an SD card file
 The circuit:
 * SD card attached to SPI bus as follows:
 ** MOSI - pin 11
 ** MISO - pin 12
 ** CLK - pin 13
 ** CS - pin 4

 created   Nov 2010
 by David A. Mellis
 modified 9 Apr 2012
 by Tom Igoe

 This example code is in the public domain.

 */

#include &lt;SPI.h&gt;
#include &lt;SD.h&gt;

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 native USB port only
  }


  Serial.print("Initializing SD card...");

  if (!SD.begin(53)) {
    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("testing1 1, 2, 3.");
    myFile.println("testing2 1, 2, 3.");
    myFile.println("testing3 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
}
</code></pre>

<p>but here he read all the contnent of the file, i want to read only testing 3 part . Thank's for help </p>
 30063: <p>i found this solution with use of strcmp:
when i read the file i compare the result str coming from file flux</p>

<pre><code>/*
 SD card read/write

This example shows how to read and write data to and from an SD card file   
The circuit:
* SD card attached to SPI bus as follows:
** MOSI - pin 11
** MISO - pin 12
** CLK - pin 13
** CS - pin 4

created   Nov 2010
by David A. Mellis
modified 9 Apr 2012
by Tom Igoe

This example code is in the public domain.

*/

#include &lt;SD.h&gt;

File myFile;
char buf[10];

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(53)) {
   Serial.println("initialization failed!");
   return;
 }
 Serial.println("initialization done.");  

 // 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()) {
      myFile.read(buf,2);       
       if(strncmp(buf, "12", 2) == 0)//for lenght i use 2 becouse im looking for a number with 2 digit
       {
           Serial.println("Match!");
           }
          break;     
       }
   }
   // 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
}
</code></pre>
