Is it good practice to use std::vector as a simple buffer?

Question

I have an application that is performing some processing on some images.

Given that I know the width/height/format etc. (I do), and thinking just about defining a buffer to store the pixel data:

Then, rather than using new and delete [] on an unsigned char* and keeping a separate note of the buffer size, I'm thinking of simplifying things by using a std::vector.

So I would declare my class something like this:

#include <vector>  class MyClass {     // ... etc. ...  public:     virtual void OnImageReceived(unsigned char *pPixels,          unsigned int uPixelCount);  private:     std::vector<unsigned char> m_pImageBuffer;    // buffer for 8-bit pixels      // ... etc. ... }; 

Then, when I received a new image (of some variable size - but don't worry about those details here), I can just resize the vector (if necessary) and copy the pixels:

void MyClass::OnImageReceived(unsigned char *pPixels, unsigned int uPixelCount) {     // called when a new image is available     if (m_pImageBuffer.size() != uPixelCount)     {         // resize image buffer         m_pImageBuffer.reserve(uPixelCount);         m_pImageBuffer.resize(uPixelCount, 0);     }      // copy frame to local buffer     memcpy_s(&m_pImageBuffer[0], m_pImageBuffer.size(), pPixels, uPixelCount);      // ... process image etc. ... } 

This seems fine to me, and I like that fact that I don't have to worry about the memory management, but it raises some questions:

1. Is this a valid application of std::vector or is there a more suitable container?
2. Am I doing the right thing performance-wise by calling reserve and resize?
3. Will it always be the case that the underlying memory is consecutive so I can use memcpy_s as shown?

Any additional comment, criticism or advice would be very welcome.

Answer 1

1. Sure, this'll work fine. The one thing you need to worry about is ensuring that the buffer is correctly aligned, if your class relies on a particular alignment; in this case you may want to use a vector of the datatype itself (like float).
2. No, reserve is not necessary here; resize will automatically grow the capacity as necessary, in exactly the same way.
3. Before C++03, technically not (but in practice yes). Since C++03, yes.

Incidentally, though, memcpy_s isn't the idiomatic approach here. Use std::copy instead. Keep in mind that a pointer is an iterator.

Starting in C++17, std::byte is the idiomatic unit of opaquely typed storage such as you are using here. char will still work, of course, but allows unsafe usages (as char!) which byte does not.