Data read separately fscanf

Question

I'm trying to read numbers from a file. The file has the following format:

2 4 5 7
3 2 4 7

I tried to do that using fscanf to collect all the numbers up to the newline and store the number in an array and the same with the second line. But proceed directly from the second line does not start again and store this in another array. Is it possible to do this using fscanf?

int main(void)
{
    FILE* fp;
    int *vec = malloc(sizeof(int)*6);
    int *vec_2 = malloc(sizeof(int)*6);
    int row, i;

    fp = fopen("vector.txt","r");

    for(i = 0; i < row; i++) //I don't know how to read until newline
        fscanf(fp, "%d", &vec[k]); //here store the first row in the array

    for(i = 0; i < row; i++)
       fscanf(fp, "%d", &vec_2[i]); //start reading here from the second row

    free(vec);
    free(vec_2);
    return 0;
}

Answer 1

row has to be initialized to 6 and possibly col too, you may use the following using two-dimensional array.

int main()
{
    FILE* fp;
    int **vec;
    int row = 6, col = 6, i, j;
    vec = malloc(sizeof(int *)*row); // allocates space for each row
    for (i = 0; i < row; i++) {
     vec[i] = malloc(sizeof(int)*col); // now allocate space for each cell within a row
    }
    fp = fopen("vector.txt","r");

    for(i = 0; i < row; i++) {
     for (j=0; j < col; j++) {
       fscanf(fp, "%d", &vec[i][j]); // read ith row, jth col
     }
    }

    vec = malloc(sizeof(int *)*row);
    for (i = 0; i < row; i++) {
       free(vec[i]);
    }    
    free(vec);
    return 0;
}

Answer 2

Anytime data is stored in lines, best to consider fgets().

This solution adapts to N rows and user selectable column width

#define MAX_INT_WIDTH (sizeof (int) * CHAR_BIT/3 + 3)

int **Read_Lines_Of_Numbers(FILE* inf, size_t Expected_Row_Width) {
  int **Row = NULL;
  size_t RowCount = 0;
  size_t RowSize = 0;
  char buf[Expected_Row_Width * (MAX_INT_WIDTH + 1) + 2];
  while (fgets(buf, sizeof buf, inf) != NULL) {
    if (RowCount >= RowSize) {
      RowSize = (RowSize + 1) * 2; // Double size
      Row = realloc(Row, RowSize * sizeof *Row);  // OOM checking omitted
    }
    Row[RowCount] = calloc(Expected_Row_Width, sizeof *Row[RowCount]); // OOM checking omitted
    size_t i;
    char *p = buf;
    for (i = 0; i < Expected_Row_Width; i++) {
      int n;
      if (sscanf(p, "%d %n", &Row[RowCount][i], &n) != 1)
        break;
      p += n;
    }
    if (*p || i != Expected_Row_Width) { // Bad data on line
      free(Row);
      return NULL;
    }
    RowCount++;
  }
  Row = realloc(Row, (RowCount + 1) * sizeof *Row);  // OOM checking omitted
  Row[RowCount] = NULL;
  return Row;
}

int main(void) {
  FILE *inf = fopen("c:/tmp/vector.txt", "r");
  size_t Width = 4;
  int **Data = Read_Lines_Of_Numbers(inf, Width);
  fclose(inf);

  if (Data) {
    size_t i;
    for (i = 0; Data[i]; i++) {
      size_t j;
      for (j = 0; j < Width; j++) {
        printf(" %d", Data[i][j]);
      }
      fputc('\n', stdout);
    }
    free(Data);
  }
  return 0;
}

Answer 3

int main(void){
    FILE* fp;
    int cols = 6;
    int *vec_1 = malloc(sizeof(int)*cols);
    int *vec_2 = malloc(sizeof(int)*cols);
    int i, i1, i2;
    char ch;

    fp = fopen("vector.txt","r");

    for(i1 = 0; i1 < cols; ){
        fscanf(fp, "%d%c", &vec_1[i1++], &ch);//Format is limited. "num[ \t\n]"
        if(ch == '\n')
            break;
    }

    i2 = 0;
    while(1==fscanf(fp, "%d", &vec_2[i2])){
        if(++i2 == cols)
            break;
    }
    fclose(fp);
    printf("first  : ");
    for(i=0; i<i1; ++i)
        printf("%d ", vec_1[i]);
    printf("\n");
    printf("second : ");
    for(i=0; i<i2; ++i)
        printf("%d ", vec_2[i]);
    printf("\n");
    free(vec_1);
    free(vec_2);
    return 0;
}