It defines the memory models to be used by some parts of the Standard Library, and most specifically, by STL containers.
Following is the declaration for std::allocator function.
template <class T> class allocator;
template <class T> class allocator;
T − It contains information about types of elements.
Type | Definition |
---|---|
value_type |
T |
pointer (deprecated in C++17) |
T* |
const_pointer (deprecated in C++17) |
const T* |
reference (deprecated in C++17) |
T& |
const_reference (deprecated in C++17) |
const T& |
size_type (deprecated in C++17) |
std::size_t |
difference_type (deprecated in C++17) |
std::ptrdiff_t |
propagate_on_container_move_assignment (C++14) |
std::true_type |
rebind (deprecated in C++17) |
template<class U >struct rebind { typedef allocator<U>other;}; |
is_always_equal (C++17) |
std::true_type |
In below example explains about std::allocator function.
#include <memory> #include <iostream> #include <string> int main() { std::allocator<int> a1; int* a = a1.allocate(10); a[9] = 7; std::cout << a[9] << '\n'; a1.deallocate(a, 10); std::allocator<std::string> a2; decltype(a1)::rebind<std::string>::other a2_1; std::allocator_traits<decltype(a1)>::rebind_alloc<std::string> a2_2; std::string* s = a2.allocate(2); a2.construct(s, "foo"); a2.construct(s + 1, "bar"); std::cout << s[0] << ' ' << s[1] << '\n'; a2.destroy(s); a2.destroy(s + 1); a2.deallocate(s, 2); }
Let us compile and run the above program, this will produce the following result −
7 foo bar