template <typename T, int num_items>
class cTest
{
public :
const int m_num_items ;
T * m_items ;
cTest () : m_num_items (num_items)
{
m_items = new T [num_items] ;
}
~cTest ()
{
delete [] m_items ;
}
cTest (const cTest &source) : m_num_items (source.m_num_items)
{
m_items = new T [num_items] ;
for (int k = 0 ; k < m_num_items ; k++)
m_items [k] = source.m_items [k] ;
}
} ;
int main (int argc, char *argv [])
{
cTest<int, 4> t1 ;
cTest<int, 4> t2 (t1) ;
return 0 ;
}
Copy Constructor and Templates
Author
I found the following on Wikipedia about the C++ copy constructor : "Contrary to expectations, a template copy constructor is not an explicit copy constructor." (Article link)
Is this true? I created the following test program in Visual Studio 2005, and it works fine.
What you have is a non-template copy constructor of a template class. What the article is referring to is template copy constructors. Ex:
template <typename U>cTest(const U & something) { // stuff}
Author
Yes, sorry, that is something different. Is that why the following does not compile?
template <typename T, int num_items>class cTest{ public : const int m_num_items ; T * m_items ; cTest () : m_num_items (num_items) { m_items = new T [num_items] ; } ~cTest () { delete [] m_items ; } cTest (const T &item) : m_num_items (1) { m_items = new T [1] ; m_items [0] = T ; // error C2275: 'T' : illegal use of this type as an expression }} ;int main (int argc, char *argv []){ cTest<int, 1> t1 ; cTest<int, 1> t2 (12) ; return 0 ;}
No, that's because you're doing the equivalent of:
You probably mean:
int a = int;You probably mean:
m_items [0] = T();
Author
Yes, I must be sleeping. I meant the following, which works:
template <typename T, int num_items>class cTest{ public : const int m_num_items ; T * m_items ; cTest () : m_num_items (num_items) { m_items = new T [num_items] ; } ~cTest () { delete [] m_items ; } cTest (const T &item) : m_num_items (1) { m_items = new T [1] ; m_items [0] = item ; }} ;int main (int argc, char *argv []){ cTest<int, 1> t1 ; cTest<int, 1> t2 (12) ; return 0 ;}
Author
I get it now. The thing is that when you have
template <typename T> cTest::cTest <const T &source) { //... }
and you use cTest for T, you get
cTest::cTest <const cTest &source) { //... }
which looks a _lot_ like a copy constructor for cTest, but isn't.
template <typename T> cTest::cTest <const T &source) { //... }
and you use cTest for T, you get
cTest::cTest <const cTest &source) { //... }
which looks a _lot_ like a copy constructor for cTest, but isn't.
This topic is closed to new replies.
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