GSL Matrix Read and Write

#include <stdio.h>
#include <stdlib.h>
#include <gsl/gsl_matrix.h>
#define N 8

int main(int argc, char **argv) {
  gsl_matrix *e = gsl_matrix_alloc(N, N);
  gsl_matrix *f = gsl_matrix_alloc(N, N);
  FILE *in;
  if (argc > 1) in = fopen(argv[1], "r");
  else in = stdin;
  gsl_matrix_fscanf(in, e);
  gsl_matrix_fscanf(in, f);
  fclose(in);
  //
  // some operation
  //
  FILE *out = fopen("output.dat", "w");
  gsl_matrix_fprintf(out, e, "%e");
  gsl_matrix_fprintf(out, f, "%e");
  fclose(out);
  gsl_matrix_free(e);
  gsl_matrix_free(f);
  return EXIT_SUCCESS;
}