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POtype conversion for struct of array from c++ to c
 

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  1. POtype conversion for struct of array from c++ to c
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    <p>I have two libraries, from C++ and C, respectively:</p> <p>lib A in C++: </p> <pre><code>typedef struct { char val[4096]; } AString; </code></pre> <p>lib B in C:</p> <pre><code>typedef struct STRING_TYPE{ unsigned char *u1_list; signed int i4_length; } BString; </code></pre> <p>If I cannot touch lib A &amp; B code, i.e., cannot add a cast operator in AString class. How to convert from AString to BString?</p> <p><strong>EDIT 1</strong>: no separate function defined:</p> <pre><code>AString as=XXX; // given variable 'as' to convert, unsigned char p[4096]; size_t const N = std::min(strlen(as.val), 4096); BString bs = { p, N }; std::copy( static_cast&lt;unsigned char*&gt;(&amp;as.val[0]), static_cast&lt;unsigned char*&gt;(&amp;as.val[N]), bs.u1_list ); // or use memcpy like: memcpy (bs.u1_list, as.val, N+1); // then follows the part to use converted variable bs; func(bs); </code></pre> <p>but the code is not module structured.</p> <p>or else:</p> <p><strong>EDIT 2</strong>: which is essentially EDIT_1, define a function, </p> <pre><code>void convert (AString&amp; as, BString&amp; bs) { size_t const N = std::min(strlen(as.val), 4096); std::copy( static_cast&lt;unsigned char*&gt;(&amp;as.val[0]), static_cast&lt;unsigned char*&gt;(&amp;as.val[N]), bs.u1_list ); // or use memcpy like: memcpy (bs.u1_list, as.val, N+1); bs.i4_length = N; } </code></pre> <p>but before call this function, the user has to define an array, like</p> <pre><code>AString as=XXX; // given variable 'as' to convert, unsigned char p[4096]; BString bs; bs.u1_list = p; convert(as, bs); // then follows the part to use converted variable bs; func(bs); </code></pre> <p>Both are quite awkward. </p> <p>Isn't there any self-contained, separate-function way to do this?</p>
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    1. COWhy is this tagged "C++" if you're using `typedef struct`?
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    2. COabove comment nitpicks
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    3. CO@marinara: Not really. C++ is as much about idioms and conventions as it is about syntax, _especially_ when dealing with code that compiles as either C++ or C. Really, though, Kerrek should have asked "why are you using `typedef struct` in C++?"
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      1. USLightness Races in Orbit
 

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