How to read scientific number from file?

clara · #1 10-Oct-2005, 00:24

Hello

I'm currently doing a set of program that handles a VRML file as input. Basically, the main programs are for parsing the input file, and another is to calculate the boundary coordinate of the whole 3D world.

I'm now having a problem of reading an input file, where the file consists of scientific number (for example: -1.26759e-006).
In my program I would read the file character by character and store it in a buffer. Afterwards, I would examine the buffer word by word.
For fields that are supposed to be numbers, my program would read it as float numbers. But I don't know how if the input is a scientific number...

Thank you for any advice..I'd really appreciate it...

WaltP · #2 10-Oct-2005, 00:44

Look up the sprintf() function. It can handle stf notation.

clara · #3 10-Oct-2005, 01:07

Thank you for the reply

I've looked up the sprintf() function and yeah, it can handle the e and E type...

then I suppose I can first read the input number as e or E type and if the function returns a negative number, that means it's an error and I can read the number as usual (float , etc)....
I hope I'm correct ...

Thanks again for the advice ^.^

davekw7x · #4 10-Oct-2005, 09:37

Quote:

Originally Posted by clara

Thank you for the reply

I've looked up the sprintf() function and yeah, it can handle the e and E type...

then I suppose I can first read the input number as e or E type and if the function returns a negative number, that means it's an error and I can read the number as usual (float , etc)....
I hope I'm correct ...

Thanks again for the advice ^.^

You can use fscanf(...,"%f"...,) to read floats and fscanf(...,"%lf",...) to read doubles. Input formats can be decimal or scientific notation. I usually use fgets() followed by sscanf(), but here's more-or-less what I would do:

CPP / C++ / C Code:

#include <stdio.h>
int main()
{
  double x, y;

  FILE *infile;
  char *inname = "test.txt";

  infile = fopen(inname, "r");
  if (!infile) {
    printf("Can't open file %s for reading\n", inname);
    return 0;
  }

  if (fscanf(infile, "%lf", &x) != 1) {
    printf("Can't read x from file %s\n", inname);
    return 0;
  }

  printf("x = %f, x = %e, x = %g\n", x, x, x);

  if (fscanf(infile, "%lf", &y) != 1) {
    printf("Can't read y from file %s\n", inname);
    return 0;
  }

  printf("y = %f, y = %e, y = %g\n", y, y, y);

  return 0;
}

And here's my file "test.txt" I used your example number in both formats.

Code:

-1.26759e-006
-.00000126759

Here's my output:

Quote:

x = -0.000001, x = -1.267590e-06, x = -1.26759e-06
y = -0.000001, y = -1.267590e-06, y = -1.26759e-06

Regards,

Dave

WaltP · #5 10-Oct-2005, 10:14

Dang, I did it again. I meant sscanf(). Sorry.

Thanks Dave...

clara · #6 10-Oct-2005, 21:50

thanks Dave and Walt

It really helps ^.^
Walt: yeah, I didn't realise that what I was looking at (even after I read your first post) was actually sscanf lol

By the way, I have another related question...
can the scientific number then be processed as a float? for example, if I want to convert a char array that contains "1.267590e-06", can I use atof function?

WaltP · #7 10-Oct-2005, 22:04

Try it. Write a test program.

clara · #8 11-Oct-2005, 03:24

yeah hehe...I'm waiting for my program to finish running first

sorry for asking that kind of question

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How to read scientific number from file?

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