read from SD card and convert to float

Projects Programming
1

Hi,

I tried to read a Dataset from a SD card on my Yun.
The Data is in a .txt doc with 4 columns (seperated with a HT) and I want to fill the first 1D array with the fisrt column and another 3D array with the other 3 columns.
I started with a unsinged char array for my incoming ASCII characters but the atof funtction can't convert it to a float number. The error message is

SD_read:59: error: invalid conversion from 'unsigned char' to 'const char*' [-fpermissive]

SerialUSB.println(atof(read_buffer[0]);

Am I using the atof function wrong?

#include <FileIO.h>

void setup() {
  // Initialize the Bridge and the Serial
  Bridge.begin();
  Serial.begin(9600);
  FileSystem.begin();

  while (!SerialUSB); // wait for Serial port to connect.
  SerialUSB.println("Filesystem datalogger\n");
}


void loop() {
  int i;
  unsigned char read_buffer[100];

  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  // The FileSystem card is mounted at the following "/mnt/FileSystema1"
  File dataFile = FileSystem.open("/mnt/sd/datalog.txt", FILE_READ);

  // if the file is available, write to it:
  if (dataFile) {
    while(dataFile.available()){
      read_buffer[dataFile.position()] = dataFile.read();
      SerialUSB.println(atof(read_buffer); 
   
    }
   //SerialUSB.println(atoi(read_buffer)); 
    //dataFile.close();
    // print to the serial port too:
    
  }
  // if the file isn't open, pop up an error:
  else {
    SerialUSB.println("error opening datalog.txt");
  }
  dataFile.close();
  delay(15000);

}

content of the datalog.txt file:

0.000	1.233	2.455	3.566
0.020	3.566	4.677	5.899
0.040	6.899	7.900	8.122
0.050	9.233	1.566	2.666
2

The atof() function operates on an array of chars terminated by a zero, otherwise known as a C style string.

Your
  SerialUSB.println(atof(read_buffer[0]); has 2 problems. The first is that the parameter being passed to atof() is not a zero terminated array of chars and secondly there is a parenthesis missing.

3

SD_read:59: error: invalid conversion from 'unsigned char' to 'const char*' [-fpermissive]

SerialUSB.println(atof(read_buffer[0]);

What do you know. The compiler is right. The atof() function takes an array, not a character. Why is the [ 0 ] in there?

   while(dataFile.available()){
      read_buffer[dataFile.position()] = dataFile.read();
      SerialUSB.println(atof(read_buffer);
   
    }

I hope that there are less than 100 characters in the file. Why are you calling atof() after adding each character? Why are you calling a function that expects a string with a char array?

You need to learn the difference between a string and a char array. Hint: A string is a NULL-terminated something.

content of the datalog.txt file:

So what should atof() convert all that text to?

4

Another choice is file.parseFloat() which should return the next value in the file.

  if (dataFile) {
    int i = 0;
    while(dataFile.available()) {
        array1[i] = dataFile.parseFloat();
        array2[i][0] = dataFile.parseFloat();
        array2[i][1] = dataFile.parseFloat();
        array2[i][2] = dataFile.parseFloat();
        i++;
        }
    }
5

I tried the version with parseFolat but it doesnt work, the error message is:

SD_read:68: error: invalid types 'float[int]' for array subscript

array2*[0] = dataFile.parseFloat();*
why can't i index a float array by writing an integer into the brackets?

6

why can't i index a float array by writing an integer into the brackets?

Who can tell from a mangled snippet?

http://snippets-r-us.com

7 
#include <FileIO.h>

void setup() {
  // Initialize the Bridge and the Serial
  Bridge.begin();
  Serial.begin(9600);
  FileSystem.begin();

  while (!SerialUSB); // wait for Serial port to connect.
  SerialUSB.println("Filesystem datalogger\n");
}


void loop() {
  int i,j;
  int inChar;
  String inString = "";
  float array1[50];
  float array2[10];
  //float array3[10]



  // open the file. note that only one file can be open at a time,
  // so you have to close this one before opening another.
  // The FileSystem card is mounted at the following "/mnt/FileSystema1"
  File dataFile = FileSystem.open("/mnt/sd/datalog.txt", FILE_READ);

  //str_buffer = '0';
  // if the file is available, write to it:
  if (dataFile) {
      i=0;
    while(dataFile.available()){

        array1[i] = dataFile.parseFloat();
        array2[i][0] = dataFile.parseFloat();
        array2[i][1] = dataFile.parseFloat();
        array2[i][2] = dataFile.parseFloat();
        SerialUSB.println(array1[i]);
        i++;
  
    /*
     if ((inChar>45)&&(inChar<58)) { 
      inString += (char)inChar;
      i++;
     }
     else if (inChar <11){
      input[i] = inString.toFloat();
      inString = "";
     }
  */
  }

    }
  // if the file isn't open, pop up an error:
  else {
    SerialUSB.println("error opening datalog.txt");
  }
  
  dataFile.close();
  //for (j=0;j<3;j++)
  //{
  /*j=0;
    for(i=0;i<4;i++){
      SerialUSB.println("erste:");
      SerialUSB.println(array2[0][0]);
    } */
  //}
  delay(30000);

}
8

You said 'three dimensional' but I assumed you meant 'two-dimensional'. Try:

 float array2[10][3];

WARNING: array1 shouldn't have to be sized for 50 lines in the file if array2 is only sized for 10 lines.

9

If the file contains plain text, what happens with this code:

  char temp;
  int count;
  static int valsRead = 0;
  

// other loop() code...
  count = 0;
  while(dataFile.available()){
      read_buffer[count] = dataFile.read();
      if (read_buffer[count] == '\t') {              // It's a tab character...
         read_buffer[count] = '\0';                  // replace it with null
         array1[valsRead++] = atof(read_buffer);     // Convert to fp number  
         count = 0;
      } else {
         count++;
      }
   }

I haven't tested this, so it's just an idea that might work.

EDIT: I forgot the else clause for count.