Question

I need to develop a simple portable C++ program Billing_Unit.
It reads some parameters (telefone number, etc.) and returns the price of call and rest of free minutes.

I decided to get data for Billing_Unit from standart input, and output result to standart output.

I developed two test units: Test_Unit_Source and Test_Unit_Destination.

I decided to organize a consecutive performing of my program units:

1. Test_Unit_Source: Reads data from database and puts it to
   standart output;
2. Billing_Unit: Reads standart output from
   previous unit, Calculates the call costs and the rest of free
   minutes, outputs result.

3. Test_Unit_Destination: Reads the call
   costs and the rest of free minutes, stores it to database.

   Test_Unit_Source | Billing_Unit | Test_Unit_Destination

Simplified Test_Unit_Source:

#include <stdio.h>
#include <iostream>
#include <fstream>
#include <string>

#define SUCCESS_RESULT 0
#define ERROR_RESULT 1

using namespace std;

int main() {
    signed char buf;

    string Name_File;
    ifstream inp_file;

    inp_file.open("temp.txt",std::ios::binary);

    if (!inp_file) return ERROR_RESULT;

    do {
        buf=inp_file.get();
        cout<<buf;
    } while (!inp_file.eof());

    return SUCCESS_RESULT;
}

Simplified Billing_Unit – it must be portable:

#include <iostream>

#define SUCCESS_RESULT 0
#define ERROR_RESULT 1

int main() {
    signed char var;
    unsigned long res;//cents
    signed char next_call;

    while (!EOF_USERS) {
        std::cin >> input_data;
            ...
        //calculations
            ...
        std::cout << result;
    }

    std::cout << EOF_USERS;

    return SUCCESS_RESULT;
}

Simplified Test_Unit_Destination:

#include <stdio.h>
#include <iostream>
#include <fstream>
#include <string>

#define SUCCESS_RESULT 0
#define ERROR_RESULT 1

using namespace std;

int main() {
    signed char buf;

    ofstream out_file;

    out_file.open("out.txt",std::ios::binary);

    if (!out_file) return ERROR_RESULT;

    while (!EOF_USERS) {
        cin >> buf;
        out_file << buf;        
    }



    return SUCCESS_RESULT;
}

Actually Test_Unit_Source and Test_Unit_Destination can be united in one program unit. It depends on my decision.

Is it a good organization of my project?
What is the best organization of this project? May be it’s better to set input parameters for Billing_Unit through command line, but I don’t know how to return the result in this case.

Answer 1

Your design fits perfectly into the model of unix-like languages: by writing your program as a filter that reads stdin and writes to stdout you’re giving users the flexibility to easily pre- or post-process the data.

For example, as you’ve written it, you can simply run

Billing_Unit < input_file > output_file

But suppose the input data is in the wrong format. Then you can run

reformat_data < input_file | Billing_Unit > output_file

And you can change the output format with

Billing_Unit < input_file | sort_by_customer > output file

These are simple examples, but I hope they show you how easy it is to work with a program like yours.

If you do plan to run your program directly from the shell like this, be sure that any error messages are written to stderr instead of stdout. That will separate them from your output data, so they won’t be processed as input by the next command.