Question

I am borring this example from the material i am going over. According to textbook, all is well here.

Yet, when trying to compile these files, i am getting a problem (see below)

3 files

Date.cpp:

    #include "Date.h"

    Date::Date()
    {
        setDate(1,1,1900);
    }

    Date::Date(int month, int day, int year)
    {
        setDate(month, day, year);
    }

Date.h:

class Date
{
public:
    Date ();
    Date (int month, int day, int year);

    void setDate(int month, int day, int year);
private:
    int m_month;
    int m_day;
    int m_year;
};

Main.cpp:

#include "Date.h"

int main () 
{
    Date d1 ;

    return 1;
}

When trying to compile with g++ *, i get

Undefined symbols for architecture x86_64:
  "Date::setDate(int, int, int)", referenced from:
      Date::Date()  in cc8C1q6q.o
      Date::Date()  in cc8C1q6q.o
      Date::Date(int, int, int) in cc8C1q6q.o
      Date::Date(int, int, int) in cc8C1q6q.o
ld: symbol(s) not found for architecture x86_64
collect2: error: ld returned 1 exit status

When i declare Date *d; instead, program compiles.
When i declare Date *d = new Date instead, program fails.

What’s going on here please?

Answer 1

You haven’t provided a setDate method for your class. You declare it in the header file but you need to provide actual code for it as well.

The error you’re seeing is the linker (ld) telling you that, although you have a piece of code trying to call that method, the linker has no idea where it is.

You need to provide the method, such as putting the following into Date.cpp:

void Date::setDate (int month, int day, int year) {
    m_month = month;
    m_day = day;
    m_year = year;
}