Question

How can I access the contiguous memory buffer used within a std::vector so I can perform direct memory operations on it (e.g. memcpy)? Also, it is safe to perform operations like memcpy on that buffer?

I’ve read that the standard guarantees that a vector uses a contiguous memory buffer internally, but that it is not necessarily implemented as a dynamic array. I figure given that it is definitely contiguous, I should be able to use it as such – but I wasn’t sure if the vector implementation stored book-keeping data as part of that buffer. If it did, then something like memcpying the vector buffer would destroy its internal state.

Answer 1

In practice, virtually all compilers implement vector as an array under the hood. You can get a pointer to this array by doing &somevector[0]. If the contents of the vector are POD (‘plain-old-data’) types, doing memcpy should be safe – however if they’re C++ classes with complex initialization logic, you’d be safer using std::copy.