Final Program Using Modules

Section 12.15 Final Program Using Modules

Here is the final program using the DateFunctions module. It requires the DateFunctions module to build. It can be compiled with the following command:

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$ g++ -std=c++20 -fmodules-ts main.cpp DateFunctions.cxx -o program.exe

Listing 12.15.1. main.cpp for use with module

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#include <iostream>

import DateFunctions;

using namespace std;

/** @brief Gets user input with a prompt and echoes it back.
 * 
 * @param prompt The prompt to display to the user.
 * @return The user input as a string.
 */
string getInput(const string& prompt) {
    string input;
    cout << prompt;
    cin >> input;
    // Echo input since activecode does not show it
    cout << endl << "You entered: " << input << endl;
    return input;
}

int main() {
    string startDate = getInput("Enter a start date in the format MM/DD/YYYY: ");
    string endDate = getInput("Enter an end date in the format MM/DD/YYYY: ");

try {
        int startDayCount = dateToDays(startDate);
        int endDayCount = dateToDays(endDate);
        int daysBetween = endDayCount - startDayCount;
        cout << "The number of days between the two dates is: "
             << daysBetween << endl;
    } catch (const logic_error& e) {
        cout << "There was an error: " << e.what() << endl;
        cout << "Please try running the program again." << endl;
    }
}

And the final unit test program. It can be compiled with the following command:

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$ g++ -std=c++20 -fmodules-ts dateTests.cpp DateFunctions.cxx -o test-program.exe

Listing 12.15.2. dateTests.cpp for use with module

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#define DOCTEST_CONFIG_IMPLEMENT_WITH_MAIN
#include "doctest.h"

import DateFunctions;

using namespace std;

TEST_CASE("getMonth") {
    CHECK(getMonth("3/4/2023") == 3);
    CHECK(getMonth("12/31/1999") == 12);
    CHECK(getMonth("1/1/2001") == 1);
}

TEST_CASE("getMonth invalid inputs") {
    CHECK_THROWS(getMonth("13/1/2023"));
    CHECK_THROWS(getMonth("abc/1/2023"));
    CHECK_THROWS(getMonth("1a5/1/2023"));
}

TEST_CASE("getDay") {
    CHECK(getDay("3/4/2023") == 4);
    CHECK(getDay("12/31/1999") == 31);
    CHECK(getDay("1/1/2001") == 1);
}

TEST_CASE("getDay invalid inputs") {
    CHECK_THROWS(getDay("3/431/2023/"));
    CHECK_THROWS(getDay("2/2023")); //only one slash
    CHECK_THROWS(getDay("3/1a/2023"));
}

TEST_CASE("getYear") {
    CHECK(getYear("3/4/2023") == 2023);
    CHECK(getYear("12/31/1999") == 1999);
    CHECK(getYear("1/1/2001") == 2001);
}

TEST_CASE("getYear invalid inputs") {
    CHECK_THROWS(getDay("2/2023")); //only one /
    CHECK_THROWS(getYear("3/4/20a23"));
    CHECK_THROWS(getYear("12/31/abcd"));
}

TEST_CASE("daysBeforeMonth") {
    CHECK(daysBeforeMonth(1) == 0);
    CHECK(daysBeforeMonth(2) == 31);
    CHECK(daysBeforeMonth(4) == 90);
    CHECK(daysBeforeMonth(12) == 334);
}

TEST_CASE("daysBeforeMonth invalid inputs") {
    CHECK_THROWS(daysBeforeMonth(0));
    CHECK_THROWS(daysBeforeMonth(13));
    CHECK_THROWS(daysBeforeMonth(-1));
}

TEST_CASE("dateToDays") {
    CHECK(dateToDays("1/1/0000") == 1);
    CHECK(dateToDays("4/10/0001") == (90 + 10 + 1 * 365));
    CHECK(dateToDays("3/14/2025") == (59 + 14 + 2025 * 365));
}

Add the code for the module itself. It can not be linked into a full program, but can be compiled. It would be compiled with something like:

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g++ -c -std=c++20 -fmodules-ts DateFunctions.cxx -o DateFunctions.o

Listing 12.15.3. DateFunctions.cxx

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module;

#include <string>
#include <stdexcept>

export module DateFunctions;

using namespace std;

// NOTE: This function is not exported, so it is only available within this module.
// It is just designed to help with the implementation of the "main" exported functions.
/** @brief Checks if a string contains only digits.
 * 
 * @param str The string to check.
 * @return true if string contains only digits, false otherwise.
 */
bool isAllDigits(const string& str) {
    for (char c : str) {
        if (!isdigit(c)) {
            return false;
        }
    }
    return true;
}

/** @brief Extracts the day from a date string in the format "MM/DD/YYYY".
 * 
 * @param date The date string to extract the day from.
 * @return The day as an integer.
 * @warning Sanity checks that the day is not > 31. Does not check for valid days in months (e.g., February 30).
 */
export int getDay(const string& date) {
    size_t slash = date.find('/');
    if (slash == string::npos) {
        throw logic_error("Date must contain '/'");
    }

string afterSlash = date.substr(slash + 1);
    size_t nextSlash = afterSlash.find('/');
    if (nextSlash == string::npos) {
        throw logic_error("Date must contain two '/' characters");
    }

string dayPart = afterSlash.substr(0, nextSlash);
    if(!isAllDigits(dayPart)) {
        throw logic_error("Day must be a number");
    }

int dayNum = stoi(dayPart);

if (dayNum < 1 || dayNum > 31) {
        throw logic_error("Day out of range");
    }

return dayNum;
}

/** @brief Extracts the year from a date string in the format "MM/DD/YYYY".
 * 
 * @param date The date string to extract the year from.
 * @return The year as an integer.
 */
export int getYear(const string& date) {
    size_t slash = date.find('/');
    if (slash == string::npos) {
        throw logic_error("Date must contain '/'");
    }

string afterSlash = date.substr(slash + 1);
    size_t nextSlash = afterSlash.find('/');
    if (nextSlash == string::npos) {
        throw logic_error("Date must contain two '/' characters");
    }

string yearPart = afterSlash.substr(nextSlash + 1);
    if(!isAllDigits(yearPart)) {
        throw logic_error("Year must be a number");
    }

int yearNum = stoi(yearPart);
    return yearNum;
}

/** @brief Extracts the month from a date string in the format "MM/DD/YYYY".
 * 
 * @param date The date string to extract the month from.
 * @return The month as an integer.
 */
export int getMonth(const string& date) {
    size_t slash = date.find('/');
    if (slash == string::npos) {
        throw logic_error("Date must contain '/'");
    }

string monthPart = date.substr(0, slash);
    if(!isAllDigits(monthPart)) {
        throw logic_error("Month must be a number");
    }

int monthNum = stoi(monthPart);

if (monthNum < 1 || monthNum > 12) {
        throw logic_error("Month out of range");
    }

// If we reach here, the month is valid
    return monthNum;
}

/** @brief Calculates the number of days before a given month in a non-leap year.
 * 
 * @param month The month to calculate the days before.
 * @return The number of days before the given month.
 */
export int daysBeforeMonth(int month) {
    //implement with switch statement
    switch (month) {
        case 1: return 0;
        case 2: return 31;
        case 3: return 59;
        case 4: return 90;
        case 5: return 120;
        case 6: return 151;
        case 7: return 181;
        case 8: return 212;
        case 9: return 243;
        case 10: return 273;
        case 11: return 304;
        case 12: return 334;
        default: throw logic_error("Invalid month");
    }
}

/** @brief Converts a date string in the format "MM/DD/YYYY" to the total number of days since the start of 0000. 1/1/0000 is considered day 1.
 * 
 * @param date The date string to convert.
 * @return The total number of days since the start of 0000.
 * 
 * @warning Assumes leap years do not exist
 */
export int dateToDays(const string& date) {
    int month = getMonth(date);
    int day = getDay(date);
    int year = getYear(date);

int totalDays = daysBeforeMonth(month) + day + year * 365;
    return totalDays;
}

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