main.cpp

#include <Arduino.h>
#include <TimeLib.h>
#include <SD.h>

char FileName[100];
void newFilename(char* FileName1);
void newFile(char* FileName1);
File myFile;

void setup() {
  Serial.begin(9600);
  while(!Serial);

  Serial.print("Initializing SD card...");
  if (!SD.begin(BUILTIN_SDCARD)) {
    Serial.println("initialization failed!");
    while (1);
  }
  Serial.println("initialization done.");
}

void loop() {
  newFilename(FileName);
  Serial.print("New FileName: ");
  Serial.println(FileName);
  newFile(FileName);
  delay(1000);
}

void newFilename(char* FileName1) {
  sprintf(FileName1, "%02d_%02d_%02d_%02d_%02d_%02d.txt", year(), month(), day(), hour(), minute(), second());
  Serial.print("New FileName1: ");
  Serial.println(FileName1);

}

void newFile(char *FileName1)
{
  myFile = SD.open(FileName1, FILE_WRITE);
  if (myFile) {
    myFile.println("testing 1, 2, 3.");
    myFile.close();
    Serial.println("done.");
  } else {
    Serial.println("error opening test.txt");
  }
}