validation of 2d array

[browser]

So I have written a program to compute the determinant of a 3x3 matrix which is read from a file....

however, I think I am missing some important validation. I get ridiculous results or infinite loops for example, when 1 entry of the 3x3 is missing, or even when 1 entry is replaced with a letter. Is there any way I can validate this before I put it in the array, or after it is in the array? Perhaps using a while loop?

And while someone is reading it, does the rest of the coding work well for what I am doing? It compiles and works fine for actual 3x3 results.

Thanks (P.S.-Only my second program so please be gentle...

/**********************************************
****Include all necessary standard libraries***
**********************************************/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/**********************************
****Define the external function***
**********************************/

double CalcDet(double matrix[][]);

/***********************
****Start the program***
***********************/

int main(void)	
{
    int         i, j;
    FILE*       input;
	double		matrix[3][3], line1, line2, line3, det;
	const char  input_fn[]="matrix.dat";
	
	input=fopen("matrix.dat","r");
	
	if (input==(FILE*) NULL)
    {
	    printf("Cannot open required file!\n");
        printf("Please ensure your matrix file\n");
	    printf("is in the correct directory\n");
	    exit(EXIT_FAILURE);
	}
	else
	{
	for(i=0; i<3; i++)
    {
        for(j=0; j<3; j++)
		{
			fscanf(input, "%lg", &matrix[i][j]);
		}
	}
	fclose(input);
	det = CalcDet(matrix);
	printf("The matrix entered and it's determinant is\n");
	printf("|%.1lg %.1lg %.1lg|\n", matrix[0][0], matrix[0][1], matrix[0][2]);
	printf("|%.1lg %.1lg %.1lg| = &.6lg\n", matrix[1][0], matrix[1][1], matrix[1][2], det);
	printf("|%.1lg %.1lg %.1lg|\n", matrix[2][0], matrix[2][1], matrix[2][2]);
	}
	return(0);
	}
	

double CalcDet(double matrix[3][3])
		{
			double  det, line1, line2, line3;
      
			line1 = ((matrix[0][0]) * ((matrix[1][1])*(matrix[2][2]) - (matrix[1][2])*(matrix[2][1])));
			line2 = ((matrix[0][1]) * ((matrix[1][0])*(matrix[2][2]) - (matrix[1][2])*(matrix[2][0])));
			line3 = ((matrix[0][2]) * ((matrix[1][0])*(matrix[2][1]) - (matrix[1][1])*(matrix[2][0])));
			
			det = line1 - line2 + line3;
	
			return(det);
		}

[Dino]

If you want to validate, you have 2 options (maybe more, but these are the practical options).

1) Read into a string and validate yourself
2) check the return value of fscanf(). See here: fscanf [C++ Reference]

[quzah]

however, I think I am missing some important validation. I get ridiculous results or infinite loops for example, when 1 entry of the 3x3 is missing, or even when 1 entry is replaced with a letter. Is there any way I can validate this before I put it in the array, or after it is in the array? Perhaps using a while loop?

You mean when your data file is corrupt you get unexpected results? How shocking!

Why don't you just read a whole line at a time and then pull each line apart?

for( x = 0; x < 3; x++ )
    if( fgets( buf, BUFSIZ, fp ) != NULL )
    {
        if( sscanf( buf, "%d %d %d", &a[x][0], &a[x][1], &a[x][2] ) == 3 )
            /*...yay...*/
        else
            /*...fail...*/
    }
    else
        /*...fail...*/

Edit: Dang phone calls.


Quzah.

[browser]

Could you explain the following construct a bit further please (and I have google'd it....)

if( fgets( buf, BUFSIZ, fp )

I understand buf has to be a character but what about BUFSIZ and would fp be my input file?

My rough attempt to understand it and apply it to my own code leads to the following...is it correct?

for( i = 0; i < 3; i++ )
    if( fgets( buf, 3, input ) != NULL )
    {
        if( sscanf( buf, "%lg %lg %lg", &matrix[i][0], &matrix[i][1], &matrix[i][2] ) == 3 )
            /*...yay...*/
        else
            /*...fail...*/
    }
    else
        /*...fail...*/

Also, I read into fscanf and I would expect it to return the value of 9, right?

Would that be;

while (fscanf (input, "%lg %lg %lg %lg %lg %lg %lg %lg %lg", matrix[0][0], matrix[0][1], matrix[0][2], .....etc) == 9)

I suppose fgets has the advantage of validating that each line has 3 values rather than just 9 values in total...are there any other advantages? Do I need to worry about EOFs?

Will fgets also get rid of any non numeric inputs and return invalid input?

Thanks

edit: Also came across this....is it helpful to me?

if( scanf("%[0987654321.-]s", buf) == 1 )
{
      if( sanit_check( buf ) ) 
      {
      /* good input */
      }
      else
      {
      /* invalid input */
      }
}
else 
{
/* invalid input */
}

[quzah]

Could you explain the following construct a bit further please (and I have google'd it....)

I find this hard to believe. You can't find information on how fgets works? Come on! The first google hit explains it:

fgets - C++ Reference

Or just use the man pages if you have them:

fgets

fgets( yourbuffergoeshere, yourbuffersizegoeshere, yourfilepointergoeshere )


Quzah.

[browser]

Right, so I tried the validation code below and it's not really working....

Any ideas

/******************************************************************
***Program to find the determinant of a 3 x 3 matrix from a file***
******************************************************************/

/**********************************************
****Include all necessary standard libraries***
**********************************************/

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

/**********************************
****Declare the external function***
**********************************/

double CalcDet(double matrix[][]);

/***********************
****Start the program***
***********************/

int main(void)	
{
    /*Define variables*/
	int         i, j, tmp;  
    FILE*       input;
	double		matrix[3][3], line1, line2, line3, det;
	const char  input_fn[]="matrix.dat";
	
	/*Open file*/
	input=fopen("matrix.dat","r");
	
	/*Verify file*/
	if (input==(FILE*) NULL)
    {
	    printf("Cannot open required file!\n");
        printf("Please ensure your matrix file\n");
	    printf("is in the correct directory\n");
	    exit(EXIT_FAILURE);
	}
	else
	{
	
	/*test code*/
	while(fscanf(input, "%.1f %.1lf %.1lf %.1lf %.1lf %.1lf %.1lf .1%lf %.1lf", matrix[0][0], matrix[0][1], matrix[0][2], matrix[1][0], matrix[1][1], matrix[1][2], matrix[2][0], matrix[2][1], matrix[2][2], &tmp) == 9);
	{
	
	/*Write matrix from matrix.dat to an array*/
	for(i=0; i<3; i++)
    {
        for(j=0; j<3; j++)
		{
			fscanf(input, "%lf", &matrix[i][j]);
		}
	}
	/*Close file*/
	fclose(input);
	
	/*Print the stored matrix and it's determinant*/
	det = CalcDet(matrix);
	printf("The matrix entered and it's determinant is\n");
	printf("|%.1lf %.1lf %.1lf|\n", matrix[0][0], matrix[0][1], matrix[0][2]);
	printf("|%.1lf %.1lf %.1lf| = %.6lf\n", matrix[1][0], matrix[1][1], matrix[1][2], det);
	printf("|%.1lf %.1lf %.1lf|\n", matrix[2][0], matrix[2][1], matrix[2][2]);
	}
	} 
	return(0);
}
	
/***********************
****End of program******
***********************/

/*********************************
****Define external function, ****
****it returns the determinant****
*********************************/
double CalcDet(double matrix[3][3])
{
	double  det, line1, line2, line3;
      
	line1 = ((matrix[0][0]) * ((matrix[1][1])*(matrix[2][2]) - (matrix[1][2])*(matrix[2][1])));
	line2 = ((matrix[0][1]) * ((matrix[1][0])*(matrix[2][2]) - (matrix[1][2])*(matrix[2][0])));
	line3 = ((matrix[0][2]) * ((matrix[1][0])*(matrix[2][1]) - (matrix[1][1])*(matrix[2][0])));
	
	det = line1 - line2 + line3;
	
	return(det);
}

[zalezog]

while(fscanf(input, "%.1f %.1lf %.1lf %.1lf %.1lf %.1lf %.1lf .1%lf %.1lf", matrix[0][0], matrix[0][1], matrix[0][2], matrix[1][0], matrix[1][1], matrix[1][2], matrix[2][0], matrix[2][1], matrix[2][2], &tmp) == 9);
	{
.
.
}

Seems like you are having trouble with an extra character.