I wonder how to get something like this:
Write
copy(a, b, 2, 3)
And then get
a[2] = b[2];
a[3] = b[3];
a[4] = b[4];
I know that C #defines can't be used recursively to get that effect. But I'm using C++, so I suppose that template meta-programming might be appropriate.
I know there is a Boost library for that, but I only want that "simple" trick, and Boost is too "messy".
You can probably do something like the following. Depending on your compiler and the optimziation settings that you use you may get the effect that you are looking for.
Be aware that for small objects like char it may well be slower than a std::copy or a memcpy and that for larger objects the cost of a loop is likely to be insignificant compared to the copies going on in any case.
#include <cstddef>
template<std::size_t base, std::size_t count, class T, class U>
struct copy_helper
{
static void copy(T dst, U src)
{
dst[base] = src[base];
copy_helper<base + 1, count - 1, T, U>::copy(dst, src);
}
};
template<std::size_t base, class T, class U>
struct copy_helper<base, 0, T, U>
{
static void copy(T, U)
{
}
};
template<std::size_t base, std::size_t count, class T, class U>
void copy(T dst, U src)
{
copy_helper<base, count, T, U>::copy(dst, src);
}
template void copy<5, 9, char*, const char*>(char*, const char*);
#include <iostream>
#include <ostream>
int main()
{
const char test2[] = " , World\n";
char test[14] = "Hello";
copy<5, 9>(test, test2);
std::cout << test;
return 0;
}
From http://www.sgi.com/tech/stl/Vector.html:
template <class InputIterator>
vector(InputIterator, InputIterator)
Creates a vector with a copy of a range.