ios::ate places the get-position pointer at the file end, enable tellg() to return the size of the f

#include <fstream>#include <iostream>#include <cstdlib>using namespace std;void print_error(const char* p1, const char* p2 = 0);int main(int argc, char* argv[]){      if (3 != argc)        print_error("usage: function input_file output_file");     ifstream in(argv[1], ios::binary | ios::ate);                          if (!in) print_error("cannot open input file", argv[1]);     long N = in.tellg();                                                   char buffer[N];                                                        in.seekg(ios::beg);                                                    ofstream out(argv[2], ios::binary);                                    if (!out) print_error("cannot open output file", argv[2]);     in.read(buffer, N);                                                    out.write(buffer, N);                                                  if (!in.good()) {        print_error("something strange happened");        exit(1);     }     in.close();     out.close();     return 0;}void print_error(const char* p1, const char* p2) {     if (p2)         cerr << p1 << ' ' << p2 << endl;     else         cerr << p1 << endl;     exit(1);}