Passing an ifstream variable to a function?

Hey all, I am writing a code used to decode text documents using caesar encryption. The program is given an encrypted text file and a code word used in that file in plain english. From there it must find the encryption key and translate the file.

It's getting hung up at this function call:

   cout << "The Caesar cipher used is "

        << findKey(infile, word);

Which links to this function:

int findKey (ifstream infile, string word){

 string buffer; //Define a string to hold each line                           

   string newCode; //Define a string to hold the converted code                 

   int found; //A int to test if the code was found                             


   for (int i = 1; i < 26; i++){ //Test input file with all keys                

      newCode = caesar(word,i);

      //Find the code word converted with each key and store as newCode         


      while( !infile.eof() ){ //Ensure file has not been read past end          

         getline (infile, buffer);

         found = buffer.find(newCode); //See if the word is in the buffer       

         if (found != string::npos){

            return i;} //Return key value if word is found                      


      }

   }

}

The error it is giving me is in the file ios_base.h, and says:
`std::ios_base::ios_base(const std::ios_base&)' is private

What am I doing wrong?

Here is the complete code if needed:


#include <iostream>

#include <string> //For the string variable                                     

#include <fstream> //To read from and to files                                  

#include <cctype> //For isupper and islower                                     

#include <cstdlib> //For exit command                                           

using namespace std;


string caesar (string, int);

int findKey (ifstream, string);


int main()

{

   //Variables declared                                                         

   string filename; //Variable for filename                                     

   string word; //Variable for the known word                                   

   ifstream infile; //Declare infile variable                                   


   cout << "Please enter the filename of the encoded message: ";

   cin >> filename;

   cout << "Please enter the known word: ";

   cin >> word;

   //The above code gets the filename and known word                            


   infile.open(filename.c_str()); //Open the inputted file                      


   if (infile.fail()){

      cout <<"File failed to open" << endl;

      exit(1); //Exits the program if file isn't found                          

   }


   cout << "The Caesar cipher used is "

        << findKey(infile, word);

   //The above code finds and outputs the key using the findKey function        


   infile.close(); //Closes input file                                          

   return 0;

}


//**************************************************************************    

//Function: caesar                                                              

//Assumption(s): A string and an int are inputted                               

//Action(s): Encrypts the string with a key of the int                          

//**************************************************************************    


string caesar (string s, int k){

   string encrypt = ""; //Declare the return variable                           

   for (int i = 0; i < s.length(); i++){ //Look at every character              

      if (isupper(s.at(i))){

         encrypt += (s.at(i)+k)%90;}

      //In the case of an uppercase letter, we need to use %90 to               

      //ensure the new letter is not greater than Z (which has value 90)        

      else if (islower(s.at(i))){

         encrypt += (s.at(i)+k)%122;}

      //In the case of a lowercase letter, we use %122 to                       

      //ensure the new letter is not greater than z (which has value 122)       

   }

   return encrypt;

}


//**************************************************************************    

//Function: findKey                                                             

//Assumption(s): An input file and a string are inputted                        

//Action(s): Outputs the encryption key using a known word                      

//**************************************************************************    


int findKey (ifstream infile, string word){

 string buffer; //Define a string to hold each line                           

   string newCode; //Define a string to hold the converted code                 

   int found; //A int to test if the code was found                             


   for (int i = 1; i < 26; i++){ //Test input file with all keys                

      newCode = caesar(word,i);

      //Find the code word converted with each key and store as newCode         


      while( !infile.eof() ){ //Ensure file has not been read past end          

         getline (infile, buffer);

         found = buffer.find(newCode); //See if the word is in the buffer       

         if (found != string::npos){

            return i;} //Return key value if word is found                      


      }

   }

}