I'm trying to compare the int number 18 with strcmp but give to me wrong result, the program looking for char 18 and not for integer 18, how i can look for an integer with strcmp?

 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];

char bufStringa[24];

void setup()
// Open serial communications and wait for port to open:
  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!");
 Serial.println("initialization done.");  

 // re-open the file for reading:
 myFile = SD.open("test.txt");
 if (myFile) {

   // read from the file until there's nothing else in it:
   int id=18;
   while (myFile.available()) {
       if(strncmp(buf, id, 2) == 0) // i think the system give to me te char 18 and not the number 18 how to do this?
           for(int i=0;i<10;i++)

            myFile.read(bufStringa, 24);
            for(int i=0;i<24;i++)

   // close the file:
 } else {
  // if the file didn't open, print an error:
   Serial.println("error opening test.txt");

void loop()
  // nothing happens after setup

Maybe make it as:

char id[] = "18";

This is if you want to find "18" in your file. That's what I understood from your question.

EDIT: I guess you want this http://playground.arduino.cc/Code/PrintingNumbers:

int num = 18;
char buffer[100]; // this will hold your number
itoa(num, buffer, 10);

Function description here. Also it's not to hard to make this your self for integers and it's a good exercise.

| improve this answer | |
  • i have an Integer for input, i need to convert this integer to char for use it in STRNCMP , tnks – Francesco Valla Feb 15 '17 at 10:24
  • Check my edit, is this what you need? – kok_nikol Feb 15 '17 at 10:30

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