Is it possible to run the FileSystem.open function using the value of a variable as the file name?

Other Hardware Storage
1

I am recording some data on the SD card and I want the file name where it is saved to be assigned by a function ...
For example:
String (file) = (("/mnt/sd/")+datactual+".csv");
File dataFile = FileSystem.open (file, FILE_APPEND);
But that doesn’t work. :frowning:

Thank you for your time.

2

Have you investigated the preprocessor's stringify operator '#'?

It may do what you want.

3

Always a very useful description of the problem. Does it not compile? Or doesn't it create a file? Or something else?

Which SD library do you use? We probably wouldn't have to ask if you had provided a complete code that demonstrates the problem and if we knew which board you're using.

Note that filenames on SD cards usually have to adhere to the 8.3 notation; so if datactual contains "Hello World", you're out of luck.

4

Not so surprising. It is incomprehensible. For all that, using a variable as a filename is common practice, the most obvious example being the use of the date:
20211101.csv.
Just stick with DOS-type 8.3 names, as mentioned above.

5

thanks for the interest, but i don't know exactly what you mean, i'm not an expert, you notice right?

6

Thanks for the interest ....

It doesn't copy the whole program because it's quite extensive, but it works, only now I want to make a modification, so far the information is always saved in the same file and I want it to be saved in a different file every month.
Test-fitxer-SD.ino (1.7 KB)

the error message when compiling is as follows:

In file included from /home/pere/Documents/Projectes/Programes per arduino/Test-fitxer-SD/Test-fitxer-SD.ino:4:0:
/snap/arduino/61/libraries/Bridge/src/FileIO.h:83:10: note: candidate: BridgeLib::File BridgeLib::FileSystemClass::open(const char*, uint8_t)
File open(const char filename, uint8_t mode = FILE_READ);
^~~~
/snap/arduino/61/libraries/Bridge/src/FileIO.h:83:10: note: no known conversion for argument 1 from 'String' to 'const char'
exit status 1

7

The compiler is objecting to the use of a String object in that function call - it was expecting a C string instead. Take a look at the String docs in the reference - you can use c_str() to solve your problem I think.

8

Code something like this, whereby a new file is created when the RTC returns a new month, i.e. midnight on the first.

#include <SD.h>
char filename[] = "000000.CSV";

void setup() {
    GetClock();
    thismonth = month; // flag for later 
    getFileName();

void loop() {  
   GetClock();
  if (thismonth != month)
  {
   thismonth = month;
   getFileName(); 
   }

void getFileName(){
sprintf(filename, "%02d%02d.csv", year, month);
}
9

Thanks for the help.
Indeed this is the problem ...
You just have to add .c_str () to the variable "file"

the function "registrar_dades () is as follows:

void registrar_dades()
{
// El fitxer es troba a "/mnt/sd/any-mes.csv"
String(file) = (("/mnt/sd/")+datactual+".csv");
File dataFile = FileSystem.open(file.c_str(), FILE_APPEND);
dataFile.println(registre);
dataFile.close();
}

The information on this link has also been very useful