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POOptimal way to fill std::vector<char> buffer
 

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  1. POOptimal way to fill std::vector<char> buffer
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    <p>This buffer should contain slots (three in this example) of equal length ( 20 in this example) <br> The buffer has to have contiguous memory so that it can be passed to a C function in non-const fashion.</p> <pre><code>const int slot_size = 20; std::vector&lt;char&gt; vbuffer; </code></pre> <p>This function takes a string, copies to a temporary buffer of the required size then appeds it to <code>vbuffer</code><br></p> <pre><code>void prepBuffer( const std::string&amp; s) { std::vector&lt;char&gt; temp(slot_size); std::copy(s.c_str(), s.c_str() + s.length() + 1, temp.begin()); vbuffer.insert(vbuffer.end(), temp.begin(), temp.end()); } </code></pre> <p>Testing the function<br></p> <pre><code>int main() { vbuffer.reserve(60); prepBuffer( "Argentina"); prepBuffer( "Herzegovina"); prepBuffer( "Zambia"); cout &lt;&lt; &amp;vbuffer[0] &lt;&lt; endl; cout &lt;&lt; &amp;vbuffer[20] &lt;&lt; endl; cout &lt;&lt; &amp;vbuffer[40] &lt;&lt; endl; } </code></pre> <p><strong>Question.</strong> There is a lot of string copying in my <code>prepBuffer</code> function. I am looking for a better way to fill up <code>vbuffer</code> with minimal copying<br> EDIT<br> The size of slots is determined elsewhere in the program. But it is not known at compile time. <br><br> <strong>EDIT</strong><br><br> In line with my accepted answer below, I have settled on this version<br></p> <pre><code>void prepBuffer(const std::string&amp; s) { assert(s.size() &lt; slot_size ); vbuffer.insert(vbuffer.end(), s.begin(), s.end()); vbuffer.insert(vbuffer.end(), slot_size - s.size(), '\0' ); } </code></pre> <p><br> Suggestions are still welcome</p>
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    1. CODo you need the different strings stored end to end? Your code would be a lot simpler if you used `std::vector<std::string>` instead.
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    2. CO@Praetorian I had anticipated such a suggestion but forgot to clarify. Just edited my question. Yes the buffer has to have contiguous memory
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