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POCross-platform ALIGN(x) macro?
 

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    <p>I would like to create a <code>struct</code> that has a certain alignment.</p> <p>I would like to use the same struct definition for both GCC and VisualC++ compilers.</p> <p>In VisualC++, one typically does this:</p> <pre><code>__declspec(align(32)) struct MyStruct { // ... }; </code></pre> <p>In GCC, one typically does this:</p> <pre><code>struct MyStruct { // ... } __attribute__ ((aligned (32))); </code></pre> <p>I could of course create the appropriate macros to make this work:</p> <pre><code>BEGIN_ALIGNED_STRUCT(32) struct { // ... } END_ALIGNED_STRUCT(32) ; </code></pre> <p>And thus be able to handle both cases transparently, but here I have to duplicate the alignment constant (<code>32</code>), which I'd like to avoid.</p> <p>An alternative in GCC is to put the <code>__attribute__</code> after the struct tag, as mentioned in <a href="http://gcc.gnu.org/onlinedocs/gcc-3.4.0/gcc/Type-Attributes.html" rel="noreferrer">the docs</a>, like so:</p> <pre><code>struct __attribute__ ((aligned (32))) MyStruct { // ... }; </code></pre> <p>And thus I could make this type of syntax work:</p> <pre><code>ALIGNED_STRUCT(32) MyStruct { // ... }; </code></pre> <p>Does anyone have any better versions? Other ideas? I tried a little code searching, but didn't find anything too promising.</p> <hr> <p><strong>Update:</strong> Based on @John's comment, here's another version that could work (I haven't compiled it, but the docs indicate it's an OK idea)</p> <pre><code>struct MyStruct_Unaligned { // ... }; TYPEDEF_ALIGNED(32, MyStruct_Unaligned, MyStruct); // Would expand to one of: // // typedef __declspec(align(32)) MyStruct_Unaligned MyStruct; // // typedef struct __attribute__ ((aligned (32))) MyStruct_Unaligned MyStruct </code></pre>
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    1. COdoes `__attribute__` work on typedef? define `struct MyUnalignedStruct {...}` and have a macro that typedefs the struct with the required alignment.
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    2. CO@John: Yes, you can, but the placement rules are the same, and thus GCC and VisualC++ are still incompatible. You can do `typedef __declspec(...) struct ...` or you can do `typedef struct __attribute__(...) ...` - I'll add that to the list, though.
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    3. COIt's unfortunate that Microsoft hasn't added support for the newly standardized `alignas` keyword.
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