在模板类中使用std :: allocator时出错

Question

Trying to figure out how to use std :: allocator.

#include <iostream>

template <typename T, typename A>
struct vector_base
{
  A       allocator;
  T*      data;
  size_t  size;
  size_t  space;

  vector_base(const A &alloc, size_t n)
    :allocator(alloc), data(alloc.allocate(n)), size(n), space(n)
  {}

  ~vector_base() {allocator.deallocate(data, space);}
};

int main() {
  std::allocator<int> my_allocator;
  vector_base<int, std::allocator<int>> vector(my_allocator, 10);

  return 0;
}

Error:

error: passing 'const std::allocator' as 'this' argument discards qualifiers [-fpermissive] :allocator(alloc), data(alloc.allocate(n)), size(n), space(n)

Answer 1

alloc is a const& , you're trying to call allocate on it which is a non-const method, that's not allowed.

Call allocate on your initialized member instead:

  vector_base(const A &alloc, size_t n)
    :allocator(alloc), data(allocator.allocate(n)), size(n), space(n)
  {}