My code doesn't compile, Im getting "/tmp/Chrono-ea8306.o: In function `operator++(Chrono::Month&)': Chrono.cpp:(.text+0x1c0): undefined reference to `Chrono::operator+(Chrono::Month const&, int)' /tmp/Chrono-ea8306.o: In function `Chrono::Date::add_day()': Chrono.cpp:(.text+0x549): undefined reference to `Chrono::operator++(Chrono::Month&)' clang: error: linker command failed with exit code 1 (use -v to see invocation) compiler exit status 1" error

---------Chrono.h----------

#ifndef CHRONO_H

#define CHRONO_H

#include "std_lib_facilities.h"

namespace Chrono

{

enum class Month

{

jan=1, feb, mar, apr, may, jun, jul, aug, sep, oct, nov, dec

};

Month operator++(Month& m); // prefix increment operator

Month operator+(const Month& m, int nMonths); // addition

Month operator+=(Month& m, int nMonths);

class Date

{

public:

class Invalid { }; // to throw as exception

Date(int yy, Month mm, int dd); // check for valid date and initialize

Date(); // default constructor

// the default copy operations are fine

// non modifying operations:

int day() const { return d; }

Month month() const { return m; }

int year() const { return y;}

// modifying operations:

void add_day(); ///add one day

private:

int y;

Month m;

int d;

bool is_valid(int y, Month m, int d); // true for valid date

int nDays(Month m); //how many days in Month m?

};

bool operator==(const Date& a , const Date& b);

bool operator!=(const Date& a , const Date& b);

ostream& operator<<(ostream& os, const Date& d);

istream& operator>>(istream& is, Date& dd);

} // Chrono

#endif

-----------Chrono.cpp----------

#include "Chrono.h"

#include "std_lib_facilities.h"

using namespace Chrono;

Date::Date(int yy, Month mm, int dd)

{

y = yy;

m = mm;

d = dd;

}

Date::Date():y{2001},m{Month::jan},d{1}

{}

int Date::nDays(Month m) {

int days_in_month;

switch (m)

{

case Month::feb: // the length of February varies

days_in_month = 28; //ignore leap year for now

break;

case Month::apr: case Month::jun: case Month::sep: case Month::nov:

days_in_month = 30; // the rest have 30 days

break;

default:

days_in_month = 31; // most months have 31 days

}

return days_in_month;

}

bool Date::is_valid(int y, Month m, int d)

{

// assume that y is valid

if (d<=0) return false; // d must be positive

if (m < Month::jan || Month::dec < m) return false;

if (nDays(m) < d) return false;

return true;

}

Month operator++(Month& m) // prefix increment operator

{

// "wrap around":

m = (m==Month::dec) ? Month::jan : Month(m+1);

return m;

}

Month operator+(const Month& m, int nMonths) // addition

{

int mInt = (int)m + nMonths - 1; ///-1 to align with [0...11] for mod

mInt %= 12; // "wrap around"

return Month(mInt + 1); ///+1 to align back with [1..12]

}

Month operator+=(Month& m, int nMonths) // addition

{

int mInt = (int)m + nMonths - 1; ///-1 to align with [0...11] for mod

mInt %= 12; // "wrap around"

m = Month(mInt + 1); ///+1 to align back with [1..12]

return m;

}

bool operator==(const Date& a, const Date& b)

{

return a.year()==b.year()

&& a.month()==b.month()

&& a.day()==b.day();

}

bool operator!=(const Date& a, const Date& b) { return !(a.year()==b.year()); }

ostream& operator<<(ostream& os, const Date& d)

{

return os << '(' << d.year()

<< ',' << int(d.month())

<< ',' << d.day() << ')';

}

istream& operator>>(istream& is, Date& dd)

{

int y, m, d;

char ch1, ch2, ch3, ch4;

is >> ch1 >> y >> ch2 >> m >> ch3 >> d >> ch4;

if (!is) return is;

if (ch1!= '(' || ch2!=',' || ch3!=',' || ch4!=')') // oops: format error

{

is.clear(ios_base::failbit); // set the fail bit (strange usage of the name "clear")

return is;

}

dd = Date(y, Month(m),d); // update dd

return is;

}

void Date::add_day() {

d++;

if(d > nDays(m))

{

d = 1;

//overloaded operators

//m = m + 1;

//m += 1;

++m;

if(m == Month::jan) y++;

}

}