fscanf .txt file to 2d matrix

[jjiyunlee]

Hi,

I'm new to C (and programming in general), and I have to say that this site has helped me learn a great deal about C (thanks everybody!!). I've looked through several discussions specifically about reading a matrix from a file, but I think (based on my admittedly small amount of knowledge about things like this) that my problem is slightly different. My for-loops for fscanf-ing values from a user-specified file seems to be ignored completely when the program below is run. Ignore void chol() and the declared values that are not used in main() - they refer to chol(), which I've left out of this post. After the filename is scanned, the program goes to the printf statement (printf("Hello");). I've been testing this program on a file test.txt that contains:

1. 2.
2. 1.

Note that, since **a is meant to be a matrix, the number of rows/columns n in this case is 2. Since this program is meant for a Cholesky decomposition, the numbers in the file are assumed to come from an nxn symmetric positive-definite matrix that, in this case, is entered by row (which is not horribly important yet since I can't read the matrix...). The block of comments before the for-loops was me checking to see if my logic in the for-loops was correct. Reading the values individually as in the comments works and gives the desired result when used on test.txt, but the for-loops seem to be skipped entirely. Now-deleted printf statements confirmed that the value of n was correctly 2 right before the for-loops, but the loop behaves as if l=n even though l is initialized at 0. The relevant loop part is in bold.

#include <stdio.h>
#include <limits.h>

main(){
char filename[FILENAME_MAX];
FILE *file;
double **a, inparen;
long n, l, m, r, s, i, j, k;
void Chol(double **, long);

printf("\nHow many columns/rows does your matrix have? ");
scanf("%lf", &n);

a=(double **)malloc(n*sizeof(double *));
*a=(double *)malloc(n*sizeof(double));

printf("\nWhat is the name of the file in which your matrix is stored? ");
scanf("%s", &filename);
file=fopen(filename, "r");
if (file==NULL){
printf("\nYour file does not exist!");
exit(1);
}

/*
fscanf(file, "%lf", &a[0][0]);
printf("%lf", a[0][0]);
fscanf(file, "%lf", &a[0][1]);
printf("%lf", a[0][1]);
*/

for (l=0;l<n;l++){
for (m=0;m<n;m++){
printf("l is %ld", l);
printf("m is %ld", m);
fscanf(file, "%lf", &a[l][m]);
printf("a[%ld][%ld] is %lf.\n", l, m, a[l][m]);
}
}

printf("\nHello");

/*
Chol(a,n);

for (r=0;r<n;r++){
for (s=r;s<n;s++){
printf("u[%li][%li] is %lf", r, s, a[r][s]);
}
}*/
}

Any helpful comments would be much appreciated :-). Thank you!!

- Joanne

[DeMan]

I suspect (but I'm not certain) that the wierd behaviour may be caused by the loop counters being initialised to Long Integers. C has some issues with casting, and I suspect in your initialisation l=0 is casting the long back to an int (why that's a problem I'm not exactly sure). if your lower loops have worked at some stage this is not the case, but it may be worth trying to declare l & m as int l,m (or if you only use them as loop counters even 'for(int l=0; l<n; l++)').

[DeMan]

I retract my earlier post....

I think the problem may be that you are reading in %lf (ie a floating point value) when you would rather read an integer %ld.