using fscanf in C with varying width files

Question

I need to write a program that reads in various files and stores the information into arrays. I will be using the doubles to perform matrix multiplies. Regarding the format of the files; the first line contains the size of the matrix. The next several lines are the rows of the matrix, where each element is separated by a space.

Format:

<number of rows> <number of columns>
<double> <double> ... <double>
<double> <double> ... <double>
.
.
.
<double> <double> ... <double>

Here are couple example files:

3 4
1.20 2.10 4.30 2.10
3.30 3.10 5.20 2.80
1.10 0.60 4.70 4.90

or

5 5
1.20 2.10 4.30 2.10 6.70
3.30 3.10 5.20 2.80 3.20
1.10 0.60 4.70 4.90 9.10
3.30 3.10 5.20 2.80 3.20
1.10 0.60 4.70 4.90 7.10

At the moment my code is as follows:

float** readFile(char* fp)
{
    float** matrix = (float**)malloc(M*N*sizeof(float));

    fp = fopen(fp, "r");

    if (fp == NULL)
    {
        fprintf(stderr, "Can't open the file\n");
        exit(1)
    }

    int i = 0;
    int m, n;
    fscanf(fp, "%d %d", m, n);
    while (fscanf(fp, "");
    {
        i++;
    }

    fclose(fp);

    return matrix;
}

and I am calling the function like this:

float** A = readFile(argv[1]);

Obviously this won't work at the moment because of the missing arguments in fscanf while reading the file. How can I use fscanf to read the values into the matrix?

Answer 1

Modify this function

float** readFile(char* file) 
{
    FILE *fp;
    float** matrix = (float**)malloc(M*N*sizeof(float));

    fp = fopen(file, "r");

    if (fp == NULL)
    {
        fprintf(stderr, "Can't open the file\n");
        exit(1)
    }

    int i = 0;
    int m, n;
    fscanf(fp, "%d %d", m, n);
    while (fgets(line,size(line),fp)!=NULL) //read file line by line
    {

use strtok() to split line into tokens with delimiter space
use strtof() to convert string to float

    }

    fclose(fp);

    return matrix;
}

Answer 2

To simply things, let us use one dimensional array. Here is the working code for you.

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

float* readFile(char* fp, int *m, int *n)/* return the dimension defined in file*/
{

    FILE *file = fopen(fp, "r");

    if (file == NULL)
    {
        fprintf(stderr, "Can't open the file\n");
                exit(1);
    }

    int i = 0, j = 0;
    fscanf(file, "%d %d[^\n]\n", m, n);
    float* matrix = (float*)malloc((*m)*(*n)*sizeof(float));

    float f;
    for (i = 0; i < *m ; ++i)
    for (j = 0; j < *n ; ++j)
    {
       fscanf(file, "%f", (matrix + i * (*n) + j));
    }


    fclose(file);

    return matrix;
}

int main()
{
    int m, n, i, j;
    float *a = readFile("a.dat", &m, &n); /* i named your data file a.dat*/

    for (i = 0; i < m ; ++i)
        {
                for (j = 0; j < n ; ++j)
                   printf("%f ", *(a + i * n + j));

                printf("\n");
        }

        free(a);
}


    /* this is the output */
1.200000 2.100000 4.300000 2.100000 6.700000
3.300000 3.100000 5.200000 2.800000 3.200000
1.100000 0.600000 4.700000 4.900000 9.100000
3.300000 3.100000 5.200000 2.800000 3.200000
1.100000 0.600000 4.700000 4.900000 7.100000

Answer 3

Here is one more version which reads the data into dynamically allocated two-dimensional array:

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

float** arralloc(int r, int c) {
    int i;
    float** arr = (float**) malloc(r*sizeof(float*));
    for (i = 0; i < r; i++)
        arr[i] = (float*) malloc(c*sizeof(float));
    return arr;
}

int main(void)
{
    int c,r,i,j;
    FILE *file = fopen("file", "r");
    fscanf(file, "%d %d\n", &r, &c);
    float** arr = arralloc(r,c);
    for (i = 0; i < r; i++){
        for (j = 0; j < c; j++){
            fscanf(file, "%f", &arr[i][j]);
            printf("%.2f ", arr[i][j]);
        }
        printf("\n");
    }
    fclose(file);
    free(arr);
}