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POTrouble figuring out why my procedure to print out bits of each integer in an array isn't working
 

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  1. POTrouble figuring out why my procedure to print out bits of each integer in an array isn't working
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    <p>I'm trying to make a class that optimizes an array of booleans by storing an ordered array of integers whose bits individual bits can be accessed to see if they're on or off. Yes, I know that </p> <pre><code>std::vector&lt;bool&gt; </code></pre> <p>does something like this, but I'm trying to make my own implementation, for practice. </p> <p>For instance, an unsigned short int is 16 bits, so I can pack 100 bools into an array of of 7 unsigned short ints where the last element acts as padding.</p> <p>As I test this, I see that something is already going wrong, possibly something with my print() function. In main you can see that I made a BitPack object of 32 bools, which will be stored in an array of 2 unsigned short ints, and I've verified that this is so. However, my print function isn't working because it gives me the following output, which isn't 32 zeros, as it should be.</p> <pre><code>0000000000000000 </code></pre> <p>I've looked over my print function numerous times and can't figure out what is wrong. Sorry about any indentations that got lost when I copied my code here. Any help greatly appreciated.</p> <pre><code>#include &lt;iostream&gt; #include &lt;limits.h&gt; #include &lt;assert.h&gt; typedef unsigned short int usi; class BitPack { public: BitPack(int); ~BitPack(); bool getVal(int); int getSize(); void setVal(int, bool); void print(); private: const static int USI_BITS = sizeof(usi)*CHAR_BIT; usi* _booArr; int _booArrLen; int _numBoos; }; BitPack::BitPack(int sz) { assert (sz &gt; 0); _numBoos = sz; _booArrLen = _numBoos/USI_BITS+(_numBoos % USI_BITS ? 1 : 0); _booArr = new usi[_booArrLen]; for (int i = 0; i &lt; _booArrLen; ++i) _booArr[i] = 0; } BitPack::~BitPack() { delete[] _booArr; } bool BitPack::getVal(int indx) { assert (indx &gt; 0); usi bA_indx_val = _booArr[indx/USI_BITS]; bA_indx_val &gt;&gt;= (bA_indx_val % USI_BITS); return (bA_indx_val % 2 ? true : false); } int BitPack::getSize() { return (_numBoos); } void BitPack::setVal(int indx, bool valset) { assert (indx &gt; 0); bool curval = getVal(indx); if ((curval == true) &amp;&amp; (valset == false)) { _booArr[indx/USI_BITS] += (1 &lt;&lt; (indx % USI_BITS)); } else if ((curval == true) &amp;&amp; (valset == false)) { _booArr[indx/USI_BITS] -= (1 &lt;&lt; (indx % USI_BITS)); } } void BitPack::print() { int i = 0; usi thisval; while (i &lt; _booArrLen - 1) { thisval = _booArr[i]; for (int j = 0; j &lt; USI_BITS; ++j) { std::cout &lt;&lt; (thisval % 2 ? '1' : '0'); thisval &gt;&gt;= 1; } i++; } thisval = _booArr[i]; for (int j = 0; j &lt; _numBoos % USI_BITS; ++j) { std::cout &lt;&lt; (thisval % 2 ? '1' : '0'); thisval &gt;&gt;= 1; } } int main (int argc, char* const argv[]) { BitPack bp(32); bp.print(); return 0; } </code></pre>
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    1. USuser2967799
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    1. PO
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    1. COHave you tried printing the values `_booArrLen` or `USI_BITS`? That should indicate pretty quickly why you're seeing an unexpected number of `0`s print.
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      1. POTrouble figuring out why my procedure to print out bits of each integer in an array isn't working
      1. USkevintodisco
    2. CODid you know vector<bool> is already optimized for space? http://www.cplusplus.com/reference/vector/vector-bool/ There is also std::bitset.
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      1. POTrouble figuring out why my procedure to print out bits of each integer in an array isn't working
      1. USPhillip Kinkade
    3. COI mentioned in my original post that I know about vector<bool>. The reason I don't like std::bitset is because it's length must be a compiler-time constant.
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      1. POTrouble figuring out why my procedure to print out bits of each integer in an array isn't working
      1. USuser2967799
 

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