c++ 2d array of class pointers - c++

Question

i am trying to create a 2d array holding pointers of my class. first, i'd like to assign all of them NULL:
Timetable::Timetable(int hours) : TimetableBase(hours){
scheduledLectures = new Lecture**[5];
for (int i = 0; i < 5; i++) {
scheduledLectures[i] = new Lecture*[hours];
for (int j = 0; j < hours; j++)
scheduledLectures[i][j] = NULL;
};
}
this is for a timetable generator application. i have a function to set these pointers to a specific object.
void Timetable::setLecture(Lecture& lecture){
while ((lecture.getDuration()) -1 > 0){
scheduledLectures[lecture.getDayScheduled()][(lecture.getHourScheduled())+1] = &lecture;
}
}
the compiler returns no errors for this, but when its running, it seems that the pointers remain NULLs.
i am sure the error is inside the setter function (and almost sure that its a grammar mistake) but i cannot find the solution for that.
whats wrong in here?
thank you

Answer 1

Use a vector (or std::array) of pointers or shared_ptrs (or unique_ptrs depending on how your lifetimes are arranged) instead of a 2D array of pointers that you manage yourself. Save yourself the trouble of managing the memory and lifetimes of your objects manually.
class TimeTable {
vector<vector<shared_ptr<Lecture>>> scheduledLectures;
};
Timetable::Timetable(int hours)
: TimetableBase(hours),
scheduledLectures(5, vector<shared_ptr<Lecture>>(5)) {}
void Timetable::setLecture(std::shared_ptr<Lecture> lecture){
while ((lecture->getDuration()) -1 > 0) { // not sure what this does
scheduledLectures[lecture->getDayScheduled()][(lecture->getHourScheduled())+1] = lecture;
}
}
You can test whether a shared_ptr is null like follows
auto s_ptr = std::shared_ptr<int>{}; // null
// either assign it to a value or keep it null
if (s_ptr) {
// not null
}
If you are managing the memory of the Lecture objects elsewhere then just use a 2D vector of pointers and trust your code
class TimeTable {
vector<vector<Lecture*>> scheduledLectures;
};
Timetable::Timetable(int hours)
: TimetableBase(hours),
scheduledLectures(5, vector<Lecture*>(5)) {}
void Timetable::setLecture(Lecture& lecture){
while ((lecture.getDuration()) -1 > 0) { // not sure what this does
scheduledLectures[lecture.getDayScheduled()][(lecture.getHourScheduled())+1] = &lecture;
}
}