Saving files to SD card with time stamp

Other Hardware Storage
3

Here is an example for SdFat.

bool openByDate(SdFile* file, uint8_t y, uint8_t m, uint8_t d);

creates a new file with a name of the form "YYMMDDNN.TXT". NN is 0-99 and makes the name unique for a given date.

#include <SdFat.h>
SdFat sd;
SdFile file;

uint8_t const chipSelect = 10;

void fmt2d(char* str, uint8_t v) {
  if (v > 99) return;
  uint8_t n1 = v / 10;
  uint8_t n0 = v - 10 * n1;
  *str++ = '0' + n1;
  *str = '0' + n0;
}

bool openByDate(SdFile* file, uint8_t y, uint8_t m, uint8_t d) {
  char name[] = "YYMMDD00.TXT";
  fmt2d(name, y);
  fmt2d(name + 2, m);
  fmt2d(name + 4, d);
  for (uint8_t n = 0; n < 100; n++) {
    fmt2d(name + 6, n);
    if (file->open(name, O_CREAT | O_EXCL |O_WRITE)) return true;
  }
  return false;
}
void setup() {
  Serial.begin(9600);
  Serial.println("type any character");
  while (Serial.available() == 0) {}
  
  if (!sd.begin(chipSelect)) {
    Serial.println("sd.begin failed");
  }
  if (openByDate(&file, 12, 3, 30)) {
    Serial.print("opened: ");
    file.printName();
    Serial.println();
  } else {
    Serial.println("open failed");
  }
}
void loop() {}

Here is a list of files created today 2012-03-30:

12033000.TXT
12033001.TXT
12033002.TXT
12033003.TXT
12033004.TXT
12033005.TXT
12033006.TXT
12033007.TXT
12033008.TXT
12033009.TXT