Input in specific format (matrix)

Question

I have an issue with input in my homework. On stdin, I will get a specifically formatted input.

In first line, there will be 2 integers, that determine the size of a matrix (rows and cols). All the lines after represent rows of the matrix.

I essentially want to do something like getline(), but I don't want to use getline(). In fact I can't, its forbidden in the homework. Therefore I have to scan int by int (or char by char I guess). The issue here is I need it to be bulletproof (almost). Dummy-proof at least.

I'm imagining a big while loop that keeps going until EOF and inside that another loop (perhaps?) which always reads a line, saves it to my allocated matrix and carries on to the next. I'm aware that I'm supposed to be checking for '\n', but I kind of lack the ability to think of a solution today.

Here's what I'm working with: My matrices are a structure.

struct Matrix{
    int nrows;
    int ncols;
    int** matrix;
};

I then have multiple functions.

A function to dynamically allocate space for the matrix of specific size:

struct Matrix init_matrix(int r, int c)
{
    struct Matrix mat;
    mat.nrows = r;
    mat.ncols = c;
    mat.matrix = calloc(r, sizeof(int *));
    for(int i = 0; i < r; ++i)
    {
        *(mat.matrix+i) = calloc(c, sizeof(int));
    }

    return mat;
}

A function to free the previously allocated space:

void free_matrix(struct Matrix mat)
{   
    int top = mat.nrows;
    for(int i = 0; i < top; ++i)
    {
        free(mat.matrix[i]);
    }
    free(mat.matrix);
}

Those 2 functions work perfectly fine.

Now I'm trying to make a function create_matrix(void) (at least I think it shouldn't take any args), that will read the input I'm supposed to receive, for example:

3 3
1 2 3
4 5 6
7 8 9

when the function reads the input, it could tell if the input is incorrect or is in incorrect format and exit the program with corresponding exit value (like 100 f.e.) If the input is correct and in correct format, it calls init_matrix() and then saves input to the matrix.

For your deeper understanding: the whole input I'm supposed to receive is: matrix A (like above, size in first line, values in lines after) an operation (+,-,*) matrix B

Then execute the operation (A*B, A+B etc.). I'm trying to make most things into functions, so the main would be very simple, f.e.

int main(int argc, char *argv[])
{
    struct Matrix mat1 = create_matrix();
    char operation = get_operation();
    struct Matrix mat2 = create_matrix();
    struct Matrix result = compute(mat1,mat2, operation);
    return 0;
}

Something in those lines, if you get me. The thing is I want to make the program complex enough so that I could later edit it to handle a bigger sequence (up to 100) of matrices than just two. Right now I could do it the dirty way, make it work for two matrices with one operation, but that's not what I really want.

Answer 1

Well, here's how I solved it. It works. It's not anywhere close to perfect, but it works, upload system took it and gave it full amount of points, so I'm satisfied.

struct Matrix read_matrix(FILE *fp)
{
    struct Matrix mat;
    //FIRST LINE
    int ch;
    int i = 0;
    int n = 20;
    char* line = calloc(n,sizeof(char));
    while((ch = fgetc(fp)) != EOF && ch != '\n')
    {
        *(line + i++) = ch;
    }
    *(line + n-1) = '\0';
    int r,c;
    int k = sscanf(line,"%d %d", &r, &c);
    if(k != 2)
    {
        fprintf(stderr, "Error: Chybny vstup!\n");
        exit(100);
    } 
    free(line);
    //MATRIX
    line = calloc(c, sizeof(int));
    mat = init_matrix(r, c);
    i = 0;
    r = 0;
    while(r < mat.nrows && (ch = fgetc(fp)))
    {
        if(ch == '\n' || ch == EOF)
        {
            *(line + i) = '\0';
            int offset;
            char *data = line;
            for(int j = 0; j < mat.ncols; ++j)
            {
                int d = sscanf(data, " %d%n", &mat.matrix[r][j], &offset);
                if(d != 1){
                    fprintf(stderr, "Error: Chybny vstup!\n");
                    exit(100);
                }
                data += offset;
            }
            i = 0;
            ++r;
            if(ch == EOF){ 
                break;
            }
        } else
        {
            *(line + i++) = ch;
        }
    }
    free(line);
    return mat;
}