Using a Constructor through pointer - c++

Question

I have a problem.
The compiler keeps warning me for invalid use of the constructor.
All i wanted to do is to create a new course in the class. whats wrong?
int StArray::addCS_Course(int id, int CourseNum, char* CourseName,int HwNum, float HwWeigh, bool Takef, char* BookName){
int i;
CS_Course* course;
if ((CourseNum<0)||(HwNum<0)||(HwWeigh<0)||(HwWeigh>1))
return 0;
for (i=0;i<StudentNum_;i++){
if (Arr_[i]->getID()==id) {
course=(CS_Course*)malloc(sizeof(CS_Course*));
if (course==NULL) {
fprintf(stderr,"Malloc failed\n");
exit(0);
}
course->CS_Course::CS_Course(CourseNum,CourseName,HwNum,HwWeigh,Takef, BookName);
if (Arr_[i]->addCS_Course(course)==1)
return 1;
else
{
free(course);
return 0;
}
}
}
return 0;
}

Answer 1

To create a new object in C++, you don't do this:
course = (CS_Course*) malloc(...);
course->CS_Course::CS_Course(...);
you do this:
course = new CS_Course(...);
That code looks after both allocating memory and calling the constructor.
You then delete your object with delete course; rather than free(course);
(But as juanchopanza points out in the comments, it's considered bad form to create objects on the heap in C style like this - you should prefer to use standard library containers and avoid the use of new. That's a whole nother discussion - you might want to read a tutorial on modern C++.)
Edit by #RemyLebeau: If you need to construct an object in existing memory, use placement new instead:
buffer = malloc(...);
course = new (buffer) CS_Course(...);
But then you have to call the destructor manually:
course->~CS_Course();
free(buffer);

Answer 2

malloc(sizeof(CS_Course*)) allocates enough space for a pointer to a CS_Course, not a CS_Course itself. If malloc were the right way to dynamically allocate memory for an object, you would need to call it like this:
malloc(sizeof(CS_Course));
However, malloc isn't the right way to do this; in C++, you use new to dynamically allocate memory for objects:
course = new CS_Course; //Use the default constructor
or
//Use constructor with 2 parameters
course = new CS_Course(constructor_param1, constructor_param2);
Of course, if you don't need a pointer, you can (and should) create a CS_Course object like this (generally referred to as allocating on the stack):
CS_Course course; //default constructor
//constructor with 2 parameters
CS_Course course2(constructor_param1, constructor_param2);