reading and printing matrix from stdin - arrays

Question

Well I posted this before but it's kinda improved now, and I only have one problem (I guess).
The assignment was to write a function which reads an integer matrix given in a ‘.txt file’ using
I/O redirection, then write another function to print it.
I read txt into a 1D array (arr) then create 2D matrix (mat) out of it, before those, I allocated memory dynamically bc our professor asked to do it that way. The problem is that arr seems to be changing when I put it on for loop and try to address it for the matrix. I would appreciate any ideas... Also, it would be helpful if you guys can comment on my way of allocating memory. (Don't forget we have 3 different input.txts some of them has -5.58234 like values or they are not seperated by "," in this example, so I want to make my code usable in any cases)
example txt file:
16, 11, 10, 16, 24, 40, 51, 61,
12, 12, 14, 19, 26, 58, 60, 55,
14, 13, 16, 24, 40, 57, 69, 56,
14, 17, 22, 29, 51, 87, 80, 62,
18, 22, 37, 56, 68, 109, 103, 77,
24, 35, 55, 64, 81, 104, 113, 92,
49, 64, 78, 87, 103, 121, 120, 101,
72, 92, 95, 98, 112, 100, 103, 99
my code:
#include <stdio.h>
#include <stdlib.h>
#include <math.h>
int readMatrix(int *arr, int **mat);
void printMatrix(int **mat, int size);
int main(){
// declare 1D array and allocate memory
int *arr;
arr = malloc(sizeof(stdin)*sizeof(int));
// declare 2D Matrix and allocate memory
int **mat;
mat = (int **)malloc(sizeof(stdin)*sizeof(int));
// function implementations
int size;
size = readMatrix(arr, mat);
printMatrix(mat,size);
return 0;
}
int readMatrix(int *arr, int **mat){
// reading
int i=0, size=0; // loop var i and size to count the elements of array
while(scanf("%d,", &arr[i]) != EOF)
{
i++;
size++;
}
printf("arr[63] = %d \n\n",arr[63]); // VALUE IS CORRECT HERE
// finding row and column numbers
int rows = sqrt(size), cols = rows;
// appending 1d array into matrix
int m = 0;
// test printf("rows = %d, cols = %d\n", rows, cols);
for(int i=0; i<rows; i++){
for(int j=0; j<cols; j++){
printf("arr[%d] = %d\n",m, arr[m]); // VALUES OF arr[] BECAME WEIRD AFTER arr[12]
//mat[i][j] = arr[m]; // segmentation fault
//*(*(mat+i)+j) = arr[m]; // segmentation fault
//*(*(mat+i)+j) = &arr[m]; // segmentation fault
*(mat + i*cols + j) = &arr[m]; // I don't know if this is the proper way but it works
m++;
}
}
printf("\narr[63] = %d\n",arr[63]); // HOWWWWW
// return size for further implementations
//
return size;
}
void printMatrix(int **mat, int size){
int rows = sqrt(size), cols = rows;
printf("\nMATRIX A:\n");
for(int i=0; i<rows; i++){
for(int j=0; j<cols; j++)
{
printf("%d ", mat[i][j]);
//if(mat[i][j]>=10 && mat[i][j]<100 ){printf("%d ", mat[i][j]);}
//else if(mat[i][j]>=100 ){printf("%d ", mat[i][j]);}
//else{printf("%d ", mat[i][j]);}
}
printf("\n");
}
}
output:
$ ./secondtry < input1.txt
arr[63] = 99
arr[0] = 16
arr[1] = 11
arr[2] = 10
arr[3] = 16
arr[4] = 24
arr[5] = 40
arr[6] = 51
arr[7] = 61
arr[8] = 12
arr[9] = 12
arr[10] = 14
arr[11] = 19
arr[12] = 976
arr[13] = 8
arr[14] = 980
arr[15] = 8
arr[16] = 984
arr[17] = 8
arr[18] = 988
arr[19] = 8
arr[20] = 992
arr[21] = 8
arr[22] = 996
arr[23] = 8
arr[24] = 1000
arr[25] = 8
arr[26] = 1004
arr[27] = 8
arr[28] = 1008
arr[29] = 8
arr[30] = 1012
arr[31] = 8
arr[32] = 1016
arr[33] = 8
arr[34] = 1020
arr[35] = 8
arr[36] = 1024
arr[37] = 8
arr[38] = 1028
arr[39] = 8
arr[40] = 1032
arr[41] = 8
arr[42] = 1036
arr[43] = 8
arr[44] = 1040
arr[45] = 8
arr[46] = 1044
arr[47] = 8
arr[48] = 1048
arr[49] = 8
arr[50] = 1052
arr[51] = 8
arr[52] = 1056
arr[53] = 8
arr[54] = 1060
arr[55] = 8
arr[56] = 1064
arr[57] = 8
arr[58] = 1068
arr[59] = 8
arr[60] = 1072
arr[61] = 8
arr[62] = 1076
arr[63] = 8
arr[63] = 8
MATRIX A:
16 11 10 16 24 40 51 61
11 10 16 24 40 51 61 12
10 16 24 40 51 61 12 12
16 24 40 51 61 12 12 14
24 40 51 61 12 12 14 19
40 51 61 12 12 14 19 976
51 61 12 12 14 19 976 8
61 12 12 14 19 976 8 980

Answer 1

Because we're reading from stdin, we can not do simple things like:
read/parse the first to determine number of columns
rewind file
read/parse all lines and store in matrix (allocating space as we go)
Note that using sqrt on the count to get number of rows/columns is a bit "unique". This is the first time I've seen that done.
When handling a 2D matrix that has dynamic dimensions, it helps to define a control struct to be able to store the dimensions. Then, all relevant info for the matrix is available to everyone.
In general, I really prefer fgets/strtok/strtol over scanf.
In this use case, I'm not sure if scanf("%d,",&val) can parse both (e.g.) 103, and 99. That is, the last number of the input file has no comma after it.
So, I had to refactor the code quite a bit. It is annotated:
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#ifdef DEBUG
#define dbgprt(_fmt...) \
printf(_fmt)
#else
#define dbgprt(_fmt...) \
do { } while (0)
#endif
// matrix control
typedef struct {
int mtx_cols; // number of columns
int mtx_rows; // number of rows (input lines)
int *mtx_base; // pointer to matrix data
} mtx_t;
// helper macro to access a given matrix coordinate
#define MTX(_mtx,_irow,_icol) \
_mtx->mtx_base[((_irow) * _mtx->mtx_cols) + _icol]
// newMatrix -- get new matrix control
mtx_t *
newMatrix(void)
{
mtx_t *mtx;
mtx = calloc(1,sizeof(*mtx));
return mtx;
}
// readMatrix -- read in matrix from stream
void
readMatrix(mtx_t *mtx,FILE *xfin)
{
char *bp;
char *cp;
char buf[1000];
// get first line as a special case to calculate the number of columns
fgets(buf,sizeof(buf),xfin);
// we need to preserve the original data for the second loop below
char tmp[1000];
strcpy(tmp,buf);
// calculate number of columns
bp = tmp;
while (1) {
char *cp = strtok(bp," ,\n");
bp = NULL;
if (cp == NULL)
break;
mtx->mtx_cols += 1;
}
// read in row by row
while (1) {
// get current row index and advance the row count
int irow = mtx->mtx_rows++;
dbgprt("BUF/%d: %s",irow,buf);
// add space for this row
mtx->mtx_base = realloc(mtx->mtx_base,
sizeof(*mtx->mtx_base) * mtx->mtx_rows * mtx->mtx_cols);
if (mtx->mtx_base == NULL) {
perror("realloc");
exit(2);
}
// parse this row
bp = buf;
for (int icol = 0; icol < mtx->mtx_cols; ++icol) {
char *cp = strtok(bp," ,\n");
bp = NULL;
if (cp == NULL)
break;
MTX(mtx,irow,icol) = strtol(cp,&cp,10);
dbgprt(" %d\n",MTX(mtx,irow,icol));
}
// get data for next row
if (fgets(buf,sizeof(buf),xfin) == NULL)
break;
}
}
void
printMatrix(const mtx_t *mtx)
{
printf("\nMATRIX A:\n");
for (int irow = 0; irow < mtx->mtx_rows; ++irow) {
for (int icol = 0; icol < mtx->mtx_cols; ++icol)
printf(" %d",MTX(mtx,irow,icol));
printf("\n");
}
}
int
main(int argc,char **argv)
{
--argc;
++argv;
FILE *xfin;
if (argc > 0)
xfin = fopen(*argv,"r");
else
xfin = stdin;
if (xfin == NULL)
exit(1);
// declare 1D array and allocate memory
mtx_t *mtx = newMatrix();
readMatrix(mtx,xfin);
printMatrix(mtx);
return 0;
}