C++11 emplace_back on vector?

Question

Consider the following program:

#include 
#include 

using namespace std;

struct T
{
    int a;
    double b;
    string c;
};

         


        

Answer 1

If you do not want to (or cannot) add a constructor, specialize allocator for T (or create your own allocator).

namespace std {
    template<>
    struct allocator {
        typedef T value_type;
        value_type* allocate(size_t n) { return static_cast(::operator new(sizeof(value_type) * n)); }
        void deallocate(value_type* p, size_t n) { return ::operator delete(static_cast(p)); }
        template
        void construct(U* p, Args&&... args) { ::new(static_cast(p)) U{ std::forward(args)... }; }
    };
}

Note: Member function construct shown above cannot compile with clang 3.1(Sorry, I don't know why). Try next one if you will use clang 3.1 (or other reasons).

void construct(T* p, int a, double b, const string& c) { ::new(static_cast(p)) T{ a, b, c }; }