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POHow to accomplish this complex mapping with template metaprogramming?
 

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  1. POHow to accomplish this complex mapping with template metaprogramming?
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    <p>I'm trying to define a struct using template metaprogramming but what I'm trying to do may need to be spread over multiple structs instead of having one super struct:</p> <pre><code>template &lt;A, B, C&gt; struct ABC { A a; B b; C c; } </code></pre> <p>Here's the flexible I hope to achieve as I will be using a code-generator and would prefer not to have to define each possible struct-type concretely if at all possible:</p> <ol> <li>Types for A, B and C can be defined.</li> <li>a, b or c can be pre-defined and pre-assigned constants (i.e, const unsigned char a = 0x48; ) or be regular variable member types.</li> </ol> <p>The general pattern is I will have unsigned numeric input for b in my code-generator, c will generally be integral (of 1-8 bytes in length) and a will be the resulting total length of the struct.</p> <p>Some examples (not exactly what is needed but to give an idea):</p> <pre><code>struct &lt;struct1&gt; { const unsigned char a = 'A'; const unsigned short b = 0x1000; char c[10]; } </code></pre> <p>I don't know enough about template meta-programming to even begin going about doing this particularly for the a and b parts where they can be pre-assigned or not.</p> <p>Perhaps to keep it easy, we can get away with assuming that I will always assign values to A, B, C and a, and b so a and b can be constants and pre-assigned.</p> <p>In the end these messages will be casted to char* and sent over the wire (and byte-packed using #pragma)</p> <p>Thanks in advance for your help!</p> <p>Sorry for the confusing problem description. I will try to clarify it with some examples of what I would like to accomplish using the templated struct ABC (or with additional structs defined as needed). These examples are from the end-user perspective:</p> <pre><code>typedef ABC&lt;100, char[10]&gt; Msg1; </code></pre> <p>would result in the equivalent of:</p> <pre><code>struct Msg1 { const unsigned short a = sizeof(Msg1); // sizeof(Msg1) fits in unsigned short const unsigned char b = 100; char[512] c; } </code></pre> <p>Note the size of members a and b need to be determined by the template based on the size of Msg1 and the passed in parameter 100. This is the tricky part for me.</p> <pre><code>typedef ABC&lt;23000, unsigned int&gt; Msg2; struct Msg2 { const unsigned char a = sizeof(Msg2); // sizeof(Msg2) fits in unsigned char const unsigned short b = 23000; unsigned int c; } </code></pre> <p>Hope this makes it a bit more clear.</p>
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      1. POHow to accomplish this complex mapping with template metaprogramming?
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    1. COHave you looked at tuples? (`std(::tr1)::tuple` or `boost::tuple`)
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      1. POHow to accomplish this complex mapping with template metaprogramming?
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    2. COSorry, I don't get at all what the problem is. What are you trying to do?
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