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<h2>eFlagBit</h2> <div class="level2"> </div> <h3>Values</h3> <div class="level3"> <span class='np_break'> </span> <div class="table"><table class="inline"> <thead> <tr class="row0"> <th class="col0"> Enum Name </th><th class="col1"> Integer Value </th><th class="col2"> Description </th> </tr> </thead> <tr class="row1"> <td class="col0"> eFlagBit_0 </td><td class="col1"> 1 </td><td class="leftalign"> </td> </tr> <tr class="row2"> <td class="col0"> eFlagBit_1 </td><td class="col1"> 2 </td><td class="leftalign"> </td> </tr> <tr class="row3"> <td class="col0"> eFlagBit_2 </td><td class="col1"> 4 </td><td class="leftalign"> </td> </tr> <tr class="row4"> <td class="col0"> eFlagBit_3 </td><td class="col1"> 8 </td><td class="leftalign"> </td> </tr> <tr class="row5"> <td class="col0"> eFlagBit_4 </td><td class="col1"> 16 </td><td class="leftalign"> </td> </tr> <tr class="row6"> <td class="col0"> eFlagBit_5 </td><td class="col1"> 32 </td><td class="leftalign"> </td> </tr> <tr class="row7"> <td class="col0"> eFlagBit_6 </td><td class="col1"> 64 </td><td class="leftalign"> </td> </tr> <tr class="row8"> <td class="col0"> eFlagBit_7 </td><td class="col1"> 128 </td><td class="leftalign"> </td> </tr> <tr class="row9"> <td class="col0"> eFlagBit_8 </td><td class="col1"> 256 </td><td class="leftalign"> </td> </tr> <tr class="row10"> <td class="col0"> eFlagBit_9 </td><td class="col1"> 512 </td><td class="leftalign"> </td> </tr> <tr class="row11"> <td class="col0"> eFlagBit_10 </td><td class="col1"> 1024 </td><td class="leftalign"> </td> </tr> <tr class="row12"> <td class="col0"> eFlagBit_11 </td><td class="col1"> 2048 </td><td class="leftalign"> </td> </tr> <tr class="row13"> <td class="col0"> eFlagBit_12 </td><td class="col1"> 4096 </td><td class="leftalign"> </td> </tr> <tr class="row14"> <td class="col0"> eFlagBit_13 </td><td class="col1"> 8192 </td><td class="leftalign"> </td> </tr> <tr class="row15"> <td class="col0"> eFlagBit_14 </td><td class="col1"> 16384 </td><td class="leftalign"> </td> </tr> <tr class="row16"> <td class="col0"> eFlagBit_15 </td><td class="col1"> 32768 </td><td class="leftalign"> </td> </tr> <tr class="row17"> <td class="col0"> eFlagBit_16 </td><td class="col1"> 65536 </td><td class="leftalign"> </td> </tr> <tr class="row18"> <td class="col0"> eFlagBit_17 </td><td class="col1"> 131072 </td><td class="leftalign"> </td> </tr> <tr class="row19"> <td class="col0"> eFlagBit_18 </td><td class="col1"> 262144 </td><td class="leftalign"> </td> </tr> <tr class="row20"> <td class="col0"> eFlagBit_19 </td><td class="col1"> 524288 </td><td class="leftalign"> </td> </tr> <tr class="row21"> <td class="col0"> eFlagBit_20 </td><td class="col1"> 1048576 </td><td class="leftalign"> </td> </tr> <tr class="row22"> <td class="col0"> eFlagBit_21 </td><td class="col1"> 2097152 </td><td class="leftalign"> </td> </tr> <tr class="row23"> <td class="col0"> eFlagBit_22 </td><td class="col1"> 4194304 </td><td class="leftalign"> </td> </tr> <tr class="row24"> <td class="col0"> eFlagBit_23 </td><td class="col1"> 8388608 </td><td class="leftalign"> </td> </tr> <tr class="row25"> <td class="col0"> eFlagBit_24 </td><td class="col1"> 16777216 </td><td class="leftalign"> </td> </tr> <tr class="row26"> <td class="col0"> eFlagBit_25 </td><td class="col1"> 33554432 </td><td class="leftalign"> </td> </tr> <tr class="row27"> <td class="col0"> eFlagBit_26 </td><td class="col1"> 67108864 </td><td class="leftalign"> </td> </tr> <tr class="row28"> <td class="col0"> eFlagBit_27 </td><td class="col1"> 134217728 </td><td class="leftalign"> </td> </tr> <tr class="row29"> <td class="col0"> eFlagBit_28 </td><td class="col1"> 268435456 </td><td class="leftalign"> </td> </tr> <tr class="row30"> <td class="col0"> eFlagBit_29 </td><td class="col1"> 536870912 </td><td class="leftalign"> </td> </tr> <tr class="row31"> <td class="col0"> eFlagBit_30 </td><td class="col1"> 1073741824 </td><td class="leftalign"> </td> </tr> <tr class="row32"> <td class="col0"> eFlagBit_31 </td><td class="col1"> -2147483648 </td><td class="leftalign"> </td> </tr> <tr class="row33"> <td class="col0"> eFlagBit_None </td><td class="col1"> 0 </td><td class="leftalign"> </td> </tr> <tr class="row34"> <td class="col0"> eFlagBit_All </td><td class="col1"> -1 </td><td class="leftalign"> </td> </tr> </table> <span class='np_break'> </span> </div> </div> <h3>Remarks</h3> <div class="level3"> <p> A flag bit is a specialized form of storing a number of boolean flags within a single integer value. This is a form of data storage that is known as a <a href="https://en.wikipedia.org/wiki/oIWIKIoBit_FieldcIWIKIc" class="interwiki iw_wp" title="https://en.wikipedia.org/wiki/oIWIKIoBit_FieldcIWIKIc">Bit Field</a>. How it works is that, rather than store values within separate boolean fields, you instead leverage bit-shift operations to use the individual bits of an integer. </p> <p> First, notice that each of the above values represent a certain power of two, going from 2⁰ (1) to 2³ (1073741824). The value for 2³¹ is also included, but due to the nature of <a href="https://www.google.com/search?q=oIWIKIoSigned_number_representationscIWIKIc&btnI=lucky" class="interwiki iw_go" title="https://www.google.com/search?q=oIWIKIoSigned_number_representationscIWIKIc&btnI=lucky">signed integers</a>, its value is -2147483648. Each of these flags represents a single 1 in the integer's binary value. For example, the binary value of 2⁵, or 32, in an integer would be 00000000000000000000000000100000 (a 1 in the sixth position). </p> <p> Because of this, if you take different flags and add them together, they will result in a value that represents a 1 in each of those flag's position. For example, adding together eFlagBit_2, eFlagBit_7, eFlagBit_12, and eFlagBit_22 will result an integer that has 1's in the third, eighth, thirteenth, and twenty-third position. (00000000010000000001000010000100, or 4,198,532.) </p> <p> In code, the way to combine different flags into a single value is pretty simple. All you do is use the <a href="https://en.wikipedia.org/wiki/oIWIKIoBitwise_operation#ORcIWIKIc" class="interwiki iw_wp" title="https://en.wikipedia.org/wiki/oIWIKIoBitwise_operation#ORcIWIKIc">bitwise-OR</a> operator to combine each desired flag into a single value. </p> <pre class="code =c++"><span class="kw4">int</span> lFlags <span class="sy0">=</span> eFlagBit_2 <span class="sy0">|</span> eFlagBit_7 <span class="sy0">|</span> eFlagBit_12 <span class="sy0">|</span> eFlagBit_22<span class="sy0">;</span> </pre><p> </p> <p> To check an integer for the presence of a flag, conversely you would use a <a href="https://en.wikipedia.org/wiki/oIWIKIoBitwise_operation#ANDcIWIKIc" class="interwiki iw_wp" title="https://en.wikipedia.org/wiki/oIWIKIoBitwise_operation#ANDcIWIKIc">bitwise-AND</a> operator. Because of how the bitwise-AND works, if you perform it on an integer and a flag, the result will be the value of the flag if the integer holds that flag, or it will be zero if not. </p> <pre class="code =c++">bool bContainsFlag <span class="sy0">=</span> <span class="br0">(</span>lFlags <span class="sy0">&</span> eFlagBit_12<span class="br0">)</span> <span class="sy0">!=</span> <span class="nu0">0</span><span class="sy0">;</span> </pre><p> </p> <p> Because bitwise operations are so fast and efficient, using a bit field in this way will result in much more efficient code than if you used standard booleans. The other upside is that a boolean variable only needs one bit to store its value (0 for false, 1 for true), but booleans still take up a full byte. Using a bit field, you can store up to 32 different flags in a single integer, meaning you are only using 4 bytes instead of 32. </p> </div>