What is the purpose of the `template <typename U> MyAlloc(const MyAlloc<U>&) { }` in the example below?

[João Affonso]

You'll find this example here (see my note at the bottom):




#include <stdlib.h>
#include <new>

template <typename T> struct MyAlloc {
typedef T value_type;

MyAlloc() { }
template <typename U> MyAlloc(const MyAlloc<U>&) { }

bool operator==(const MyAlloc&) const { return true; }
bool operator!=(const MyAlloc&) const { return false; }

T * allocate(const size_t n) const {
if (n == 0) {
return nullptr;
}

if (n > static_cast<size_t>(-1) / sizeof(T)) {
throw std::bad_array_new_length();
}

void * const pv = malloc(n * sizeof(T));

if (!pv) {
throw std::bad_alloc();
}

return static_cast<T *>(pv);
}

void deallocate(T * const p, size_t) const {
free(p);
}
};

#include <vector>
using MyIntVector = std::vector<int, MyAlloc<int>>;

#include <iostream>

int main ()
{
MyIntVector foov = { 1701, 1764, 1664 };

for (auto a: foov) std::cout << a << " ";
std::cout << "\n";

return 0;
}

I tried to set up a link in the word "here" above, but Visual C++ didn't allow me to do that. But you can find the example in



C++ Language Reference > Basic concepts > Declarations and definitions > Aliases and typedefs

Continue reading...