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

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  1. POIs it good practice to use std::vector as a simple buffer?
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    <p>I have an application that is performing some processing on some images.</p> <p>Given that I know the width/height/format etc. (I do), and thinking just about defining a buffer to store the pixel data:</p> <p>Then, rather than using <code>new</code> and <code>delete []</code> on an <code>unsigned char*</code> and keeping a separate note of the buffer size, I'm thinking of simplifying things by using a <code>std::vector</code>.</p> <p>So I would declare my class something like this:</p> <pre><code>#include &lt;vector&gt; class MyClass { // ... etc. ... public: virtual void OnImageReceived(unsigned char *pPixels, unsigned int uPixelCount); private: std::vector&lt;unsigned char&gt; m_pImageBuffer; // buffer for 8-bit pixels // ... etc. ... }; </code></pre> <p>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:</p> <pre><code>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(&amp;m_pImageBuffer[0], m_pImageBuffer.size(), pPixels, uPixelCount); // ... process image etc. ... } </code></pre> <p>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:</p> <ol> <li>Is this a valid application of <code>std::vector</code> or is there a more suitable container?</li> <li>Am I doing the right thing performance-wise by calling <code>reserve</code> <em>and</em> <code>resize</code>?</li> <li>Will it <em>always</em> be the case that the underlying memory is consecutive so I can use <code>memcpy_s</code> as shown?</li> </ol> <p>Any additional comment, criticism or advice would be very welcome.</p>
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    1. USRoger Rowland
    1. USRoger Rowland
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    1. COCan I suggest using `std::vector::assign` instead of `memcpy` and (sometimes) resize? That will resize if necessary, and avoid the unnecessary initialization of the buffer.
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      1. USmfontanini
    2. CO@mfontanini so I can `assign` a block of memory to the `vector`? Can you show me the syntax?
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      1. USRoger Rowland
    3. COThe size of the buffer gets adjusted to the correct size before the call to `memcpy_s`, so the size check in `memcpy_s` is redundant. `memcpy` is sufficient here. It doesn't make much difference in this example, but in general, once you've dealt with possible buffer overflows, checking for them again just needlessly complicates the code.
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      1. USPete Becker
 

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