Thread: Reading a 2D array from a file, compiles but doesnt work properly

Hello, im beginning to write a program to calculate the determinant of a 3x3 matrix - i need to read the elements of the matrix from an external file matrix.dat (contains 9 numbers, 3 rows, 3 columns seperated by spaces)

I have written the first part of the program - reading from the file: It compiles but doesnt work, i got it to print a value from the matrix to see if it read it but when i run the program it says 0.00000, implying a problem

where have i gone wrong? thanks so much!

Code:

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

/*need to use an external function to computer det of a minor (2x2 matrix)*/
/*Need to read from a file named matrix.dat*/

/* Prototype your function here, also make sure you change all of these comments*/
int ReadFromFile(float fullmatrix[3][3], FILE *input);

int main(int argc, char* argv[])
{
    FILE         *input;
    int           i, j;  
    float         fullmatrix[3][3];
    const char    inp_fn[]="matrix.dat";
    
    /* Open files */
    input = fopen(inp_fn, "r");
    /* Check the pointers to files are not NULL, also check matrix has correct number of elements */
    if( (input != (FILE*) NULL) )
    {
      for(i=0; i<3; i++)
	  {
	  for(j=0; j<3; j++)
	  {
	  fullmatrix[i][j]=ReadFromFile(fullmatrix, input);
	  }
	  fscanf(input, "\n");
      }
    fclose(input);
	printf("%f", fullmatrix[2][2]);
	return(0);
	}
 else
   {
    printf("*** Could not open input file, or there are not 9 elements in the matrix ***\n");
   }
}  
/*Write the external fucntion here, need a 2 dimensional array http://www.dfstermole.net/OAC/harray2.html*/

int ReadFromFile(float fullmatrix[3][3], FILE *input)
{
float element; 
fscanf(input,"%i,", &element);
return (element);
}

Thanks a lot! that was the problem... it works now.

I still have quite a bit to do on it so i may post again here in a few hours

Okay i have a problem again, it does read the file: but it does it in a weird order.

Matrix.dat contains:

Code:

1.001 -2.2000 3.1366
5.8111 9.0003 -1.1064
-3.3098 2.8243 4.5333

My program looks like

Code:

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

/*need to use an external function to computer det of a minor (2x2 matrix)*/
/*Need to read from a file named matrix.dat*/

/* Prototype your function here, also make sure you change all of these comments*/
float ReadFromFile(float fullmatrix[3][3], FILE *input);
float minordet(float minor[2][2]);

int main(int argc, char* argv[])
{
    FILE         *input;
    int           i, j;  
    float         fullmatrix[3][3];
    const char    inp_fn[]="matrix.dat";
	
    /* Open files */
    input = fopen(inp_fn, "r");
    /* Check the pointers to files are not NULL, also check matrix has correct number of elements */
    if( (input != (FILE*) NULL) )
    {
      for(i=0; i<3; i++)
	  {
	  for(j=0; j<3; j++)
	  {
	  fullmatrix[i][j]=ReadFromFile(fullmatrix, input);
	  }
	  fscanf(input, "%f");
      }
    fclose(input);
	printf("%f %f %f\n %f %f %f\n %f %f %f\n", fullmatrix[0][0], fullmatrix[0][1], fullmatrix[0][2], fullmatrix[1][0], fullmatrix[1][1], fullmatrix[1][2], fullmatrix[2][0], fullmatrix[2][1], fullmatrix[2][2]
);
	return(0);
	}
 else
   {
    printf("*** Could not open input file, or there are not 9 elements in the matrix ***\n");
   }
}  
/*Write the external fucntion here, need a 2 dimensional array http://www.dfstermole.net/OAC/harray2.html*/

float minordet(float minor[2][2])
{
float minordet;
}

float ReadFromFile(float fullmatrix[3][3], FILE *input)
{
float element; 
fscanf(input,"%f,", &element);
return (element);
}

and when it is run it shows

Code:

1.001 -2.2000 3.1366
9.0003 -1.1064 -3.309800
4.5333 4.5333 4.5333

Any idea what the problem is?

Commas don't belong in format codes for scanf()/fscanf()/sscanf().

Your function doesn't need the parameter of the array to read a number from a file - just a suggestion to remove it for cleaner code.

Originally Posted by Adak

Your function doesn't need the parameter of the array to read a number from a file.

Sorry, which bit in the code are you referring to specifically here? Also, do you have any idea why the matrix that the program prints is not the same as the one that it is reading from? do i have a problem with the for loops?

Thanks a lot

Originally Posted by stahta01

Likely this line. Tim S.

Code:

fscanf(input,"%f,", &element);

I have removed the comma from inside the quotation marks, yet the problem persists, could you point me in the right direction? Thanks