Using a String uses a lot of program sketch space!

Using Arduino Programming Questions
#1

I have created a sketch that logs data points onto a Micro SD card. The sketch will count the number of files in the “LogFiles” folder, and then create another file that is that amount plus one.

I create the new file using the function below:

void createNewFile() {
  String FileName =  String("LogFiles/Log0") + fileCount + String(".csv");
  logFile = SD.open(FileName, FILE_WRITE);
}

The issues is that this function with strings uses an extra 1,792 bytes in my program! Is there a way to do what I want to do without using strings or lowering the program storage space?

#2

Using "S"trings at all might be just the start of your troubles. You might use char instead, as is common practice.

char filename[] = "00000000.CSV";

and go on from there.

#3

Nick_Pyner:
Using "S"trings at all might be just the start of your troubles. You might use char instead, as is common practice.

char filename[] = "00000000.CSV";

and go on from there.

That saves a lot of space using char! Thank you! But how would I implement the fileCount variable into the char? For example, I am currently doing this, but get the error: "initializer fails to determine size of 'FileName'"

char FileName[] = char("LogFiles/Log0") + fileCount;
#4

I'm afraid what you are doing is meaningless, I just use the date as a filename and make new ones at midnight. So, at a guess it will be something like

sprintf(filename, "%04u.csv", fileCount);  //9999 files
fileCount++;

but I have no idea what makes the change, or why.

#5

sprintf will pull in a lot of code also, so it's not really worth it, if you only use it in one place.

It easily can be done 'by hand'.

char fName[] = "LogFiles/Log00000.csv";
const byte lastDigit = sizeof(fName) - 6;

void nextFileName() {
  if (++fName[lastDigit] > '9') {
    fName[lastDigit] = 0;
    if (++fName[lastDigit - 1] > '9') {
      fName[lastDigit - 1] = 0;
      if (++fName[lastDigit - 2] > '9') {
        fName[lastDigit - 2] = 0;
        if (++fName[lastDigit - 3] > '9') {
          fName[lastDigit - 3] = 0;
        }
      }
    }
  }
}
void setup() {
  Serial.begin(250000);
  Serial.println(fName);
  nextFileName();
  Serial.println(fName);
}
void loop() {}

LogFiles/Log00000.csv
LogFiles/Log00001.csv
#6

Whandall:
sprintf will pull in a lot of code also, so it's not really worth it, if you only use it in one place.

It easily can be done 'by hand'.

char fName[] = "LogFiles/Log00000.csv";

const byte lastDigit = sizeof(fName) - 6;

void nextFileName() {
  if (++fName[lastDigit] > '9') {
    fName[lastDigit] = 0;
    if (++fName[lastDigit - 1] > '9') {
      fName[lastDigit - 1] = 0;
      if (++fName[lastDigit - 2] > '9') {
        fName[lastDigit - 2] = 0;
        if (++fName[lastDigit - 3] > '9') {
          fName[lastDigit - 3] = 0;
        }
      }
    }
  }
}
void setup() {
  Serial.begin(250000);
  Serial.println(fName);
  nextFileName();
  Serial.println(fName);
}
void loop() {}

LogFiles/Log00000.csv
LogFiles/Log00001.csv

probably that should be (everywhere you overflow)fName[lastDigit] = '0'; // the char '0' not the null char

#7

Absolutely :wink: the test was not deep enough.

char fName[] = "LogFiles/Log00000.csv";
const byte lastDigit = sizeof(fName) - 6;

void nextFileName() {
  if (++fName[lastDigit] > '9') {
    fName[lastDigit] = '0';
    if (++fName[lastDigit - 1] > '9') {
      fName[lastDigit - 1] = '0';
      if (++fName[lastDigit - 2] > '9') {
        fName[lastDigit - 2] = '0';
        if (++fName[lastDigit - 3] > '9') {
          fName[lastDigit - 3] = '0';
        }
      }
    }
  }
}
void setup() {
  Serial.begin(250000);
  Serial.println(fName);
  for (uint16_t i = 0; i < 3456; i++ ) {
    nextFileName();
  }
  Serial.println(fName);
}
void loop() {}

LogFiles/Log00000.csv
LogFiles/Log03456.csv
#8

:slight_smile:

(I assume it's intended to not update the first 0 - ie max number is 9999)

#9

I was inspired from the

char FileName[] = char("LogFiles/Log0") + fileCount;

which also has a leading zero and I reused the limit (which is really 10000 for the same format) from

sprintf(filename, "%04u.csv", fileCount);  //9999 files
#10

I just made the 9999 up.

#11

yeah, assumed so but weird decision from OP

  String FileName =  String("LogFiles/Log0") + fileCount + String(".csv");
#12