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POCasting long int as a struct pointer
 

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    <p>I know this is a rather noobish question, but no amount of googling or permutations of code seem to work.</p> <p>I have a structure which is defined like this.</p> <pre><code>typedef struct { int rate; int duration; } DummyStructure; </code></pre> <p>Now, i try to use code similar to this.</p> <pre><code>// DummyStructure* structure; DummyStructure* structure2; long int point; // structure = (DummyStructure*)malloc(sizeof(DummyStructure)); structure-&gt;rate = 19; structure-&gt;duration = 92; point = (long int)&amp;structure; // now i'd like to set structure2 to the same memory location as 1. // point is the 8-byte int location (i assume?) of structure. // so naturally i'd assume that by casting as a DummyStructure pointer // that long int would act as a pointer to that 1. // It doesn't. structure2 = (DummyStructure*)point; </code></pre> <p>I stress that i've tried every permutation of ** and * that is possible. I just don't get it. Either it doesn't compile, or it does, and when it does i end up with seemingly random numbers for the fields contained in structure2. I assume that somehow i'm winding up with an incorrect memory location, but how else can you get it except from using the &amp;?</p> <p>I have the memory location, right? How do i set the structure to that location?</p> <p>EDIT; I forgot to mention (and subsequent answers have asked) but i'm intending to use this to wrap libvorbis for jni. Using jni means that i can't pass-back any of the structs that libvorbis does, but it requires them for its core functions. Therefore my wrapper is going to use vorbis directly to make the structs, and i pass back to java the pointer to them so that when i need to fill the buffer with more sound, i can simply re-reference the struct objects from the integer value of the pointer.</p>
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    1. CONote that you should not be casting the return value from `malloc(3)` -- simply `#include <stdlib.h>` and you will get the `malloc(3)` prototype that allows the compiler to handle everything for you. These casts can hide compiler warning messages that alert you to bugs in your code.
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      1. USsarnold
    2. COMost likely `long` isn't long enough to hold a pointer value. You'll probably have better results with `(u)intptr_t`, `size_t`, or `long long`.
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      1. USAlexey Frunze
    3. COOut of curiosity, why are you using a long int at all?
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      1. USKeith Irwin
 

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