How to make std::vector reuse a given memory block? [duplicate]

This question already has an answer here:

• Is it possible to initialize std::vector over already allocated memory? 3 answers

A memory block holds values I'd like to use as an std::vector. I currently copy the values over using std::memcpy.

#include <cstdlib>
#include <cstring>
#include <vector>
int main()
{
    const std::size_t count = 2097152;
    float* ptr = (float*)std::malloc(count * sizeof(float)); // raw ptr for simplicity
    // ...
    std::vector<float> vec(count, 0);
    std::memcpy(vec.data(), ptr, count * sizeof(float));
    //...
    std::free(ptr);
}

However the copying is unnecessary, since ptr is no longer needed at this point. How can I make std::vector reuse the memory and take normal ownership of it?