/*
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 (for MKRZero SD: SDCARD_SS_PIN)
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>
#define LINELEN 19 // length of line including EOL characters, I assume crlf 0x0D 0x0A
// so the line is actually 32 text characters plus 2 end of line characters for 34 total.
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(10)) {
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("testA.txt");
// if the file opened okay, write to it:
if (myFile) {
uint32_t line=1;
uint32_t S= (line-1)*LINELEN;
myFile.seek(S); //position the 'file pointer' to where I want to start over-writing.
char ch[20]; // got to remember c++ strings need a \0 to mark the end.
// build the 'delete line'
for(uint8_t i=0;i<17;i++) ch[i]=' ';
ch[17]='\r'; // (cr)
ch[18]='\n'; // newline (lf)
ch[19]='\0'; // end of string marker;
// over write (delete) the existing data
myFile.print(ch); // all marked as deleted! yea
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("testA.txt");
if (myFile) {
Serial.println("testA.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
}
17 characters are there in that line ...but it wont delete the line ..
now i can delete first line:
i removed spaces between characters;;;;
/*
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 (for MKRZero SD: SDCARD_SS_PIN)
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>
#define LINELEN 15 // length of line including EOL characters, I assume crlf 0x0D 0x0A
// so the line is actually 32 text characters plus 2 end of line characters for 34 total.
static uint32_t line=1;
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(10)) {
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("testC.txt",FILE_WRITE);
// if the file opened okay, write to it:
if (myFile) {
uint32_t S= (line-1)*LINELEN;
myFile.seek(S); //position the 'file pointer' to where I want to start over-writing.
char ch[15]; // got to remember c++ strings need a \0 to mark the end.
// build the 'delete line'
for(uint8_t i=0;i<13;i++) ch[i]=' ';
ch[13]='\r'; // (cr)
ch[14]='\n'; // newline (lf)
ch[15]='\0'; // end of string marker;
// over write (delete) the existing data
myFile.print(ch); // all marked as deleted! yea
/* Serial.print("Writing to test.txt...");
for(int i=0;i<=10;i++){
myFile.print(i);
myFile.println("testing1,2,3");
}*/
// 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("testC.txt");
if (myFile) {
Serial.println("testA.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 i want to update second line as a first line ..
means whenever loop executes it should delete first line..
actually i am having face detection machine..whenever face detected data to be stored in sd card in text file ..and sent that text file data through gprs tcp /ip to the server tcp port...
i have got success in following things:
1: getting wiegand out ID from FACE detection machine ...
2:used rtc ds1307 to get time and date
3:ID+DATE+TIME string is stored in SD card text file Line by Line
4:reading first line from text file from sd card after every 15 Minutes and send it through gprs tcpip
5:got success in sending first line to tcp port
6:and also compared the response of gprs module with "OK" When AT+CIPSEND succeeded..
7:store that successfully sent string to another text file
i have stuck in this:
when i successfully sent (first line of text file)to tcp port and store that string in another text file
:in next iteration want to send next line of text file(2nd line)..and so on
means i want to send whole text line by line to tcp port..
