SD.open() returns true but does not create a file

问题

I'm facing a specific problem with SD card and Arduino. I want to create a function that creates a new file on the SD card for a different day. For now, I'm simulating calendar with ints. I know that problem was already discussed but I can't seem to find a similarly discussed problem.

Code:

#include <stdlib.h> // included for floatToString 
#include <math.h> 
#include <SPI.h>
#include <SD.h>

int year = 2014;
int month = 11;
int day = 4;

char dateTitle[20]; //= "0000000000.txt";

void printDateTitle(char* dateTitle, int Y, int M, int D){
  //char dateTitle[20];
  sprintf(dateTitle, "%4d-%02d-%02d.txt", Y, M, D);
  return;
}

const int chipSelect = 4;

void setup() {
  //printDateTitle(dateTitle, year, month, day);
  Serial.begin(9600);
  while (!Serial) {
    ;
  }
  Serial.print("Initializing SD card...");
  if (!SD.begin(chipSelect)) {
    Serial.println("Card failed, or not present");
    while (1);
  }
  Serial.println("card initialized.");
}

void loop() {
  Serial.print(dateTitle);
  delay(1000);
  File dataFile = SD.open(dateTitle, FILE_WRITE);
  if (dataFile){
    dataFile.println("something");
    dataFile.close();
    Serial.print(day);
    Serial.println("something");
    delay(1000);
  } else 
    Serial.println("Error");
}

In the code, I have a function void printDateTitle that formats the inputs from the calendar to string which I want to use as a title for the file.

And also, when I define a function in the void loop() with printDateTitle(dateTitle, year, month, day); I get an "Error" in the output meaning SD.open = false.

The problem is that even though SD.open returns true it doesn't create a file on the SD card. .txt is included in the char array. I have also used capital .TXT.

I would be grateful for all the bits of advice regarding the problem.

For the reference, I'm using Arduino Uno and Micro SD card Adapter with Arduino IDE.

回答1:

The Arduino SD Library documentation states that it uses the "short 8.3 names for files". Therefore only files with 8 characters as name and 3 for file extension are valid. For example: 12345678.txt is valid, 123456789.txt would be invalid.

Your date string (2014-11-04.txt) is to long because it has 10 characters instead of only 8.

Also make sure you've formatted the SD card to a FAT16 or FAT32 file system.

来源：https://stackoverflow.com/questions/47664817/sd-open-returns-true-but-does-not-create-a-file

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arduino