need help with fread

ns

I just posted and deleted my post because I feel its incredibly dumb. (What I want to do I know how to with CSdioFIle and atof, but I want to try with fread). I have a txt file that looks like this:

with the leading spaces (4 spaces). I copied this data from matlab and pasted into notepad. I want to load this data into an array of doubles. I did the following but evidently I dont know how to use fread inspite of re-reading the docs and googling. It just doesnt click :(

FILE\* fpRed = fopen("red64.txt", "r");
if (!fpRed ) return;

double red64\[64\];

while  (!feof(fpRed))
{
	for (int i = 0; i < 64; i++)
	{
		fread(red64+i, sizeof(double), 10, fpRed);

		double r = red64\[i\];
	}
}
	fclose(fpRed);

I put down 10 because its 4 white spaces + 6 spaces in the number itself. If theres invisible stuff in the file I dont know...... :confused: Thanks for helping, ns

Vancouver

Are you sure there are four spaces at the beginning, and not one tab?

ns

It backs up one by one four spaces. If it were a tab what would I do for nItemstoRead? Anyways for the first few elements I removed the spaces so there numbers start flush at the left, and yet when I step through I get garbage. This time I said nItems = 6 since 0.5000 etc. Thanks for helping, ns

Antti Keskinen

First of, fread fills a buffer you specify with characters read from the file. Characters are different from numbers. For example, a char number[2] = "32" is NOT the same thing as int a = 32 Secondly, a file is just lots of characters placed sequentically, with occasional control markers placed between. There are NO NUMBERS there. So you just cannot read doubles from a file. That just does not work. Now, let's redo this thing..

// Open the file in text mode
FILE* fInput = fopen("red64.txt", "rt");

if ( !fInput )
return;

// Create buffers to hold readed data and temporary data
char buffer[20] = { NULL };
char number[8] = { NULL };
double red64[64];

// Access the file
int nDoublePos = 0;

while ( !feof(fInput) )
{
// Read a line from the file
fgets( &buffer[0], 19, fInput );

  // Step through the line, copying digits and decimal points
  int nPosition = 0;
  int nLinePos = 0;

  while ( buffer\[nLinePos\] != '\\n' )
  {
       if ( isdigit( buffer\[nLinePos\] ) || buffer\[nLinePos\] == '.' )
       {
              // Copy it to the buffer
              number\[nPosition++\] = buffer\[nLinePos\];
       }

        // Move to next character on the line
       nLinePos++;
   }

   // Now we have readed one double value into a character string, so convert
   if ( number\[0\] != NULL )
        red64\[nDoublePos++\] = atof( &number\[0\] );

   // Clear the buffers & move to the next line
   memset( &buffer\[0\], 0, sizeof(buffer) );
   memset( &number\[0\], 0, sizeof(number) );

}

Here's a basic idea on how the conversion is implemented. First we read a line to the

nss

Thank you so much for your detailed response! I see I had totally misunderstood fread! I'll check it out. I had thought CStdioFile and atof was too circuitous but I now see that fread is also doing chars..... thanks, ns

John R Shaw

:)Good answer! Minor detail: char number[2] = "32"; // Outch: char number[2] = {'3','2','\0'} Should be char number[3] = "32"; // Ok even in our sleep. ;)Sorry automatic reaction when I see a line of code (even example code) that makes my heart skip a beat. INTP