Passing a string to ofstream

Enforcer83 (2)
I have code that developes a string. I intend to pass this string to ofstream for the file name. What is the right way of doing so?

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// Pass string to output file stream as filename
ofstream file(comp);


or

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// Cast string as character array for filename
char complete = static_cast<char>(comp);

// Pass char array to output file stream as filename
ofstream file(complete);


The second method is currently giving me a compile error (can't remember error as I am not at computer that I am developing the code on).

Or should I be doing this a completely different way?

Below is my full code.

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//------------------------------------------------------------------------------------------//
//                                                                                          //
// Developer:  (NOT DISCLOSED FOR POST)                                                     //
// Developed:  15 MARCH 2012                                                                //
// Filename:   clock.cpp                                                                    //
//                                                                                          //
// Copyright 2012, (NOT DISCLOSED FOR POST)                                                 //
//                                                                                          //
//                                                                                          //
// This program is free software: you can redistribute it and/or modify it under the terms  //
// of the GNU General Public License as published by the Free Software Foundation, either   //
// version 3 of the License, or any later version.                                          //
//                                                                                          //
// This program is distributed in the hope that it will be useful, but WITHOUT ANY          //
// WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A          //
// PARTICULAR PURPOSE.  See the GNU General Public License for more details.                //
//                                                                                          //
// You should have received a copy of the GNU General Public License along with this        //
// program.  If not, see <http://www.gnu.org/licenses/>.                                    //
//                                                                                          //
//------------------------------------------------------------------------------------------//

#include <iostream>
#include <fstream>
#include <sstream>
#include <string>
#include <iomanip>

using namespace std;

int main () {
     
     //Setup String Stream object
     stringstream ss (stringstream::in | stringstream::out);
     
     //Declare and initialize necessary system variables
     int found = 0;
     float fin = 0, fout = 0, n, m, p, nMax = 4096, mMax = 512;
     float pMax = 128;
     string first = "pll_m_n_p_";
     string middle = "_";
     string end = ".txt";
     
     // Prompt user for input and output frequencies
     cout << "Welcome to the CDCE706 PLL configurator./n/n";
     cout << "Please enter your desired input and output frequencies in MHz." << endl << endl;
     cout << "Input: ";
     cin >> fin;
     cout << endl << "Output: ";
     cin >> fout;
     cout << endl;
     
     // Check to see if fequencies are within chip capabilities
     if ((fin <= 200) && (fout <= 300)) {
          
          // Output float values as strings
          ss << fin;
          string in = ss.str();
          
          ss << fout;
          string out = ss.str();
          
          // Combine all strings for filename
          string comp = first + in + middle + out + end;
          
          cout << "Output being sent to file " << comp;
          cout << endl << endl;
          
          // Cast string as character array for filename
          //char complete = static_cast<char>(comp);
          
          // Pass string to output file stream as filename
          //ofstream file(complete);

          // Pass char array to outpul file stream as filename
          ofstream file(comp);
          
          // check if file is open other wise
          if (file.open()) {
               
               // Setup column headers
               file << "M Value\t" << "N Value\t" << "P Value\n" << endl;
               
               // Process all possible compinations of settings
               for ( n = 0; n < nMax; n++) {

                    for ( m = 0; m < mMax; m++) {

                         for ( p = 0; p < pMax; p++) {
                              
                              // Check to see if current combination meets chip criteria
                              if (((fin * n)/(m * p)) == fout) && ((n/m) >= 1)) {
                                   
                                   // Tell system combination was found.
                                   found = 1;
                                   
                                   // Output combination to file.  (Two tabs required for
                                   // proper formatting)
                                   file << m << "\t\t";
                                   file << n << "\t\t";
                                   file << p << endl << endl;

                              }

                         }

                    }
                    
               }

               // Close the file
               file.close();
               
          }
          
          // Terminate program
          else {
               
               cout << "No file open.  Exiting." << endl;
               
               return(1);
               
          }
          
          // Check if a combination was found
          if (!found) {
               
               // Inform user no combination found
               cout << "Sorry.  I was unable to find any matches." << endl;
               cout << "Please try a different input frequency.  Goodbye." << endl;

          }
          
          else {
               
               // Other wise tell user processing complete
               cout << "Done.  Thank you.";
               
          }
     
     // Inform user of proper input and output frequency range
     else {
          
          cout << "Input/Ouput frequency to high." << endl;
          cout << "Limits: In - 200MHz; Out - 300MHz." << endl;
          cout << "Goodbye.";
          
     }
     
     // Terminate program successfully.
     return(0);

}
Last edited on
viliml (791)
either the first way or
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// Cast string as character array for filename
const char* complete = static_cast<const char*>(comp);

// Pass char array to output file stream as filename
ofstream file(complete);
coder777 (8450)
@viliml: No

This is how it has to be done:
ofstream file(complete.c_str());
JLBorges (13770)
The std::ofstream constructor which takes a std::string is not available in old C++. It is there in C++11.
http://en.cppreference.com/w/cpp/io/basic_ofstream/basic_ofstream
Enforcer83 (2)
So for backwards compatability with older compilers use:

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// Cast string as character array for filename
const char* complete = static_cast<const char*>(comp);

// Pass char array to output file stream as filename
ofstream file(complete.c_str());
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