Question

I try to read file /proc/’pid’/status, using c program. The code is as follows, and even I use sudo to run it, the prompt still keeps throwing “Unable to open file”. Please let me know if you have any ideas on how to fix this. thanks

Richard

…

int main (int argc, char* argv[]) {  
  string line;  
  char* fileLoc;  
  if(argc != 2)  
  {  
     cout << "a.out file_path" << endl;  
     fileLoc = "/proc/net/dev";  
  } else {  
     sprintf(fileLoc, "/proc/%d/status", atoi(argv[1]));  
  }  
  cout<< fileLoc << endl;  

  ifstream myfile (fileLoc);  
  if (myfile.is_open())  
  {  
    while (! myfile.eof() )  
    {  
      getline (myfile,line);  
      cout << line << endl;  
    }  
    myfile.close();  
  }  

  else cout << "Unable to open file";  

  return 0;  
}  

Answer 1

Avoid using C strings in C++. You forgot to allocate this one. A stringstream will allocate for you and has sprintf functionality.

int main (int argc, char* argv[]) {  
  string line;
  ostringstream fileLoc;
  if(argc != 2)  
  {  
     cout << "a.out file_path" << endl;  
     fileLoc << "/proc/net/dev";  
  } else {  
     fileLoc << "/proc/" << argv[1] << "/status";
  }  
  cout<< fileLoc.str() << endl;  

  ifstream myfile (fileLoc.str().c_str());