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POC++ Can't Write 1's To Struct Member
 

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  1. POC++ Can't Write 1's To Struct Member
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    <p>I'm having a little problem writing 1's to a struct's member.</p> <p>I have a struct which represents a Voxel which can have 8 children (IDs 0-7). In order to state which children a Voxel has I'm using an unsigned 8-bit integer. If the Voxel has a certain child, then the bit at the position in the children member that equals the child's ID is set to 1.</p> <p>For example, if a Voxels children member stored the value: 10000101 Then the Voxel would have children 0, 2 and 7 (from right to left).</p> <p>The code for the Voxel struct is as below:</p> <pre><code>typedef struct Voxel { uint8_t children; //list of children Voxel* firstChildPointer; }; </code></pre> <p>First child pointer points to the start of a list of voxels which are this voxels children.</p> <p>The problem occurs when wanting to add a child. I need to change the children member to reflect the added child. When doing this however, I get a runtime exception saying "Access violation writing location" followed by a memory address.</p> <p>The code I use to change the children is below:</p> <pre><code>void addVoxel(Voxel* parent, char childID) { parent-&gt;children |= (1 &lt;&lt; childID); } </code></pre> <p>When all the Voxels are first loaded into memory the Voxel's children is set without error. But after that I cannot write 1's to the member. 0's write perfectly fine. I have tried using many methods to write things, even a plain old assignment to a number. But if the number has more 1's then it won't work.</p> <p>It so happens that a pointer to the parent in this case it stored as a global variable, and each voxel also stores a pointer to it's children, could this be the problem? If so would passing the parent as a reference help? I know how to do this in C# but not in C++.</p> <p>Any help would be great.</p> <p>S.</p> <p>EDIT:</p> <p>The add voxel method is called using this line:</p> <pre><code>addVoxel(octree, 4); </code></pre> <p>octree is a voxel pointer as defined by:</p> <pre><code>Voxel* octree = octreeLoader.loadVoxelData(); </code></pre> <p>The load voxel data method loads octree information from a file. We know that this section and the return pointer work as we use an exact duplicate of them to ray trace. However in short the pointer is created using this line:</p> <pre><code>Voxel* octree; </code></pre> <p>And then assigned memory using this line:</p> <pre><code>octree = (Voxel *) calloc(1, sizeof(Voxel)); </code></pre> <p>Children is then assigned using this line:</p> <pre><code>octree[0].children = children; </code></pre> <p>Each further child is then created and given memory in the same way. I have checked the children member is initialised correctly and the childID is correct.</p>
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    1. USSam 'River Prince' Stockton
    1. USSam 'River Prince' Stockton
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      1. VTUpMod
    1. COHow do you call the function? Sounds like `parent` is an invalid pointer.
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      1. POC++ Can't Write 1's To Struct Member
      1. USR. Martinho Fernandes
    2. COI call it using this line: addVoxel(octree, 4); octree is just a pointer to a voxel. The first Voxel in the tree
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      1. USSam 'River Prince' Stockton
    3. COWhat Martinho said - "parent" is likely corrupt.
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      1. USselbie
 

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