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Reading a file within a factory, tokenising, vector
Templates example from a Well House Consultants training course
More on Templates [link]

This example is described in the following article(s):
   • Reading files, and using factories to create vectors of objects from the data in C++ - [link]

Source code: flow4.cpp Module: C238
#include <iostream>
#include <fstream>
#include <vector>

/* Practical example of reading from a file within a factory
and creating a vector of objects. Also include splitting attributes
from within each line of data as the object is defined

See earlier example flow2.c which uses an array rather than a vector
for more detaied comments on the basic elements in this example */

using namespace std;

// -------------------------------

class Train {
                Train(char *);
                static Train* factory();
                int getcapacity();
                static ifstream *datasource;
                int ncars;
                int spv;

// -------------------------------

ifstream * Train::datasource = NULL;

Train* Train::factory() {
        char trainline[256];
        if (! datasource) {
                datasource = new ifstream("trains.txt");
        if (datasource->eof()) {
                return NULL;
        // Next line for demonstration
        cout << trainline << endl;
        return new Train(trainline);

Train::Train(char * source) {

// Source line example: Train 06:45 3 75

        int starts[4];
        int k=0;
        int param=0;
        while (source[k] != '\0') {
                if (source[k] == ' ') {
                        source[k] = '\0';
                        starts[param++] = k+1;
                if (param > 3) break;

        this->ncars = atoi(&source[starts[2]]);
        this->spv = atoi(&source[starts[1]]);

int Train::getcapacity() {
        return (int)(this->ncars * this->spv * 1.4);

// -------------------------------

int main () {
        // Train *service[10];

        // Create me a vector to contain train services

        // a service is a pointer to a collection of trains (LHS)
        // set up a new empty collection on the heap (RHS)

        vector<Train *> *service = new vector<Train *>(0);
        int k;

        Train *current;

        while (1) {
                current = Train::factory();
                if (! current) break;
                // service[traincount++] = current;

        // Add the new train from the factory onto the service vector


        for (k=0; k<service->size(); k++) {
                // cout << service[k]->getcapacity() << endl;

        // get the service at position "k" and then get its capacity

        // We could use an intermediate variable - code would be longer
        // ... but easier to follow.

                cout << service->at(k)->getcapacity() << endl;

        return 0;


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 "Templates" training module. You'll find a description of the topic and some other closely related examples on the "Templates" module index page.

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