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POVariable order and memory addressing in stack memory
 

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    <blockquote> <p><strong>Possible Duplicate:</strong><br> <a href="https://stackoverflow.com/questions/1102049/order-of-local-variable-allocation-on-the-stack">Order of local variable allocation on the stack</a> </p> </blockquote> <p>(C program on x86_64 Linux) I am trying to understand the way variables are assigned to stack memory. As I understand it, variables in a stack frame move toward lower memory addresses. The program below shows this.</p> <pre><code>int main() { int i = 6; char buffer[8]; return 0; } </code></pre> <p>Program was compiled as: gcc -g prog.c</p> <p>Debugging shows:</p> <pre><code>(gdb) x/x &amp;i 0x7fffffffe04c: 0x00000006 (gdb) x/x buffer 0x7fffffffe040: (random data) </code></pre> <p>The character array has a lower memory address than the integer i variable. My question is how come when the order of declarations are reversed as seen below, the integer variable i is still at a memory address greater than the character array?</p> <pre><code>int main() { char buffer[8]; int i = 6; return 0; } (gdb) x/x &amp;i 0x7fffffffe04c: 0x00000006 (gdb) x/x buffer 0x7fffffffe040: (random data) </code></pre> <p>This issue does not seem to occur for the ordering of say strictly single integer variables. If the order of integer declarations were switched, the earliest declared would have a higher memory address in the stack frame. The concern here is why this occurs for the character array. I have read this answer here in <a href="https://stackoverflow.com/questions/1102049/order-of-local-variable-allocation-on-the-stack">another post</a> but I am wondering if anyone has a definitive explanation on this one.</p>
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    1. USJohnathan1
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    1. COI'm sorry but I really don't see why this question is any different than the one you linked to. The answers there are pretty good.
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      1. USEmil Vikström
    2. CO@Emil yes, they are 'pretty' good. However, it seems the answers in that post are more of hypotheses as opposed to answers backed by facts or referenced information. I really would like to know if anyone has something more concrete.
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      1. USJohnathan1
    3. COThere isn't anything concrete. A compiler can allocate any address it sees fit to any variable, in any order. It can even use the same address for different variables that are not used at the same time. Or put the value in a register, and not allocate an address at all.
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      1. USBo Persson
 

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