error in opening files

[nanger]

using namespace std;

#include <iostream>

#include <fstream>
#include <string>

  string filename[9];
  filename[0]="output/prob_search_fail.txt";
  filename[1]="output/prob_download_fail.txt";
  filename[2]="output/avg_download_per_sec.txt";
  filename[3]="output/avg_duration_per_search.txt";
  filename[4]="output/avg_num_copy.txt";
  filename[5]="output/prob_absence_content.txt";
  filename[6]="output/distribution_content.txt";
  filename[7]="output/avg_num_copy_detail.txt";
  filename[8]="output/prob_absence_content_detail.txt";
  
  fstream outfile[9];
  for(int i=0;i<9;i++)
  {
    outfile[i].open(filename[i].c_str(),fstream::out|fstream::app);
    if(!outfile[i].is_open())
    {
      cout<<"open file "<<i<<" error\n";
      exit(1);
    }
  }
  

my error is:open file 0 error
what is wrong with my codes?
Tx!

[kbw]

Do the files exist in the currect directory the program is running in? If you're not sure, try using the full path for one of the filenames.