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Wholesale factory - a single call to make many objects
I/O in C++ example from a Well House Consultants training course
More on I/O in C++ [link]

This example is described in the following article(s):
   • C++ - putting the language elements together into a program - [link]

Source code: fullapp2.cpp Module: C235
#include <iostream>
#include <fstream>
#include <vector>
// Following 2 includes added Jan, 2011
#include <string.h>
#include <stdlib.h>

using namespace std;

/* A further step towards a complete applcation, adding in a usage line
and transferrring the building of the data model in a vector into a
function which itself calls a factory method. This approach leads towards
extensible and reuasable code, with the factory method being (in due course)
stored and maintained in the files that relate to the object type rather
than within the application itself. */


class Thing {
        public:
                Thing(char *);
                char * about();
                static vector<Thing *> * wholesalefactory(char *fylenayme);
        private:
                char definition[256];
        };

Thing::Thing (char * instring) {
        strncpy(definition,instring,255);
        }

char * Thing::about() {
        return definition;
        }

vector<Thing *> * Thing::wholesalefactory (char * sourcefile) {
        char myline[256];
        vector<Thing *> *lynes = new vector<Thing *>(0);

        ifstream infile(sourcefile);
        if (! infile) {
                cerr << "Failed to open input file "<< sourcefile << endl;
                exit(1);
                }

        while (1) {
                infile.getline(myline,256);
                if (infile.eof()) break;

// Rather than new "Thing" I could have a test to see what type of thing
// I'm going to be using ... and then create various different types.

// "Then it will be a proper factory" say my delegates! ;-)

                lynes->push_back(new Thing(myline));
                }
        infile.close();
        return lynes;
        }

main(int argc, char **argv) {

        if (argc < 2) {
                cerr << "Usage: " << *argv << " sourcefilename" << endl;
                exit(2);
                }

        vector<Thing *> * shapethings = Thing::wholesalefactory(argv[1]);

        for (int k=shapethings->size()-1; k>=0; k--){
                cout << shapethings->at(k)->about() << endl;
        }
}

/* Sample Output

munchkin:c5 grahamellis$ ./fullapp2
Usage: ./fullapp2 sourcefilename
munchkin:c5 grahamellis$ ./fullapp2 nosuchfile.txt
Failed to open input file nosuchfile.txt
munchkin:c5 grahamellis$ ./fullapp2 boring.data
Rectangle 19
Circle 6
Circle 5
Square 15
Square 20
munchkin:c5 grahamellis$

*/

Learn about this subject
This module and example are covered on the following public courses:
 * Learning to program in C and C++
 * C++ for C Programmers
 * C and C++ Programming
 * Learning to program in C and C++
 * C and C++ Programming
Also available on on site courses for larger groups

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Other Examples
This example comes from our "I/O in C++" training module. You'll find a description of the topic and some other closely related examples on the "I/O in C++" module index page.

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