Calling a constructor from the body of another constructor [duplicate] - c++

Question

This question already has an answer here:
Is there a way to do constructor delegation using a conditional in C++11?
(1 answer)
Closed 4 years ago.
The typical way (and the only one widely used) to delegate some part of the object initialization to another constructor is to call it using the initializer list, like so:
class Window
{
Window(int a);
Window(int a, void *b);
Window(string a);
Window(double a, double b) : Window((int) (a + b))
{
}
};
But sometimes there is a necessity to do some prep work or branch constructor calls.
Is this how it should be done?
class Window
{
Window(int a);
Window(int a, void *b);
Window(string a);
Window(double a, double b)
{
if (a * b == 0.0)
{
Window("ZERO");
}
else if (a * b > 100.0)
{
Window((int) (a + b), x);
}
else
{
Window((int) (a + b));
}
}
};
I have never seen anything like this; this is just my guess of how it could look (which appears to be working).
Are there any side effects or any undefined behavior to calling other constructors from the constructor body (and not from the initializer list)?
#Edit: I'm including the code I'm having a problem with below. Basically, I have an object that is a container for some data, and I store it in a std::map<CString, ValueContainer>. I employ a copy constructor, and an overloaded assignment operator. The insertion works fine when I add an instance to the map using the [] operator, but it doesn't when I use the insert_or_assign method, because it uses the copy constructor (which uses the branching that is the problem here). Here's a simplification of the class.
class ValueContainer
{
ValueContainer(const VOID *p_data, ULONG p_size)
{
if (p_data != NULL)
{
if (p_size > 0)
{
if (p_size <= sizeof(shortData))
{
memcpy(shortData, p_data, p_size);
}
else
{
longData = new BYTE[p_size];
memcpy(longData, p_data, p_size);
}
}
hasValue = TRUE;
size = p_size;
}
else
{
hasValue = FALSE;
size = 0;
}
}
ValueContainer(const ValueContainer &p_value)
{
if (p_value.HasValue())
{
if (p_value.size <= sizeof(shortData))
{
ValueContainer(p_value.shortData, p_value.size);
}
else
{
ValueContainer(p_value.longData, p_value.size);
}
}
else
{
ValueContainer();
}
}
ValueContainer(VOID) : ValueContainer(NULL, 0)
{
}
ValueContainer &operator =(const ValueContainer &p_value);
{
if (p_value.hasValue)
{
if (p_value.size <= sizeof(shortData))
{
if (longData != NULL)
{
free(longData);
longData = NULL;
}
memcpy(shortData, p_value.shortData, p_value.size);
}
else
{
if (p_value.size > size)
{
longData = (BYTE *) realloc(longData, p_value.size);
}
memcpy(longData, p_value.longData, p_value.size);
}
hasValue = TRUE;
size = p_value.size;
}
else
{
if (longData != NULL)
{
free(longData);
longData = NULL;
}
hasValue = FALSE;
size = 0;
}
return *this;
}
private:
BYTE shortData[16];
BYTE *longData = NULL;
BOOL hasValue;
ULONG size;
}

Answer 1

For your first example, this might be the way it can be done:
class Window
{
private:
void constructor_method(int a);
void constructor_method(int a, void *b);
void constructor_method(string a);
public:
Window(int a) {
constructor_method(a);
}
Window(int a, void *b) {
constructor_method(a, b);
}
Window(string a) {
constructor_method(a);
}
Window(double a, double b)
{
if (a * b == 0.0)
{
constructor_method("ZERO");
}
else if (a * b > 100.0)
{
constructor_method((int) (a + b), x);
}
else
{
constructor_method((int) (a + b));
}
}
};

Answer 2

I think the short answer to this question is "simplify your code." But if that's not an option, I think the next best alternative is a factory method:
class Window
{
private:
Window(int a);
Window(int a, void *b);
Window(string a);
public:
static Window Create(double a, double b)
{
if (a * b == 0.0)
{
return Window("ZERO");
}
else if (a * b > 100.0)
{
return Window((int) (a + b), x);
}
else
{
return Window((int) (a + b));
}
}
};