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POC++ vector on arduino takes up massive RAM footprint
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  1. POC++ vector on arduino takes up massive RAM footprint
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    copied!<p>Couldn't find a solution to this anywhere. Hoping to become more enlightened on this subject. </p> <p>I wanted to use a dynamic array of sorts for an arduino project. I came across a library for using vectors on the arduino platform <a href="https://github.com/maniacbug/StandardCplusplus" rel="nofollow">here</a>. I used a function to monitor free RAM on the arduino that I found <a href="http://www.controllerprojects.com/2011/05/23/determining-sram-usage-on-arduino/" rel="nofollow">here</a>. </p> <p>Here is an example of my code:</p> <pre><code>Serial.print("Starting RAM: "); Serial.println(freeRam()); Serial.println(); vector&lt;int&gt; intVector; Serial.print("Remaining RAM after intVector declaration: "); Serial.println(freeRam()); Serial.println(); vector&lt;char&gt; charVector; Serial.print("Remaining RAM after charVector declaration: "); Serial.println(freeRam()); Serial.println(); Serial.print("sizeof(intVector) = "); Serial.println(sizeof(intVector)); Serial.print("sizeof(charVector) = "); Serial.println(sizeof(charVector)); </code></pre> <p>And here's the output:</p> <pre><code>Starting RAM: 1684 Remaining RAM after intVector declaration: 1618 Remaining RAM after charVector declaration: 1584 sizeof(intVector) = 7 sizeof(charVector) = 7 </code></pre> <p>It seems that the intVector allocation took up a 66 byte chunk of the RAM. It appears the vector allots 32*2 + 2 = 66 bytes of memory for this. Likewise, the charVector allocation took up 34 bytes (32*1 + 2). It seems this pattern of allocating 32*<code>sizeof(type)</code> + change exists for other data types (such as char, float, etc). Note that <code>sizeof(int) = 2</code> on arduino. </p> <p>My problem is that the objects I would like to populate these vectors with are anywhere from 10-20 bytes large. With only 2 kB of RAM available on the ATMega328, I won't be able to run my program as it's currently designed. For an object <code>segment</code> with <code>sizeof(segment) = 16</code>, a vector eats up a 522-byte block of RAM. </p> <p>So my questions are:</p> <ol> <li><p>Why does the vector allocate 32 * sizeof(type) bytes of RAM when the size of the vector is only 7 bytes, despite its type?</p></li> <li><p>Is there a better way to use a sort of dynamic array on the arduino platform? </p></li> <li><p>Are there memory management techniques that may allow me to use vectors?</p></li> </ol> <p>Thanks, and sorry in advance if this question is a duplicate!</p> <p>EDIT:</p> <p>It seems that the vector is initialized with a capacity of 32. </p> <pre><code>intVector.capacity() = 32; </code></pre> <p>Attempting to use either </p> <pre><code>intVector.reserve(1); // or intVector.resize(1); </code></pre> <p>does not alter the capacity of the vector. </p>
 

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