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POHow to manage endianess of double from network
 

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    <p>I have a BIG problem with the answer to this question <a href="https://stackoverflow.com/questions/2673409/swap-bits-in-c-for-a-double">Swap bits in c++ for a double</a></p> <p>Yet, this question is more or less what I search for: I receive a double from the network and I want to encoded it properly in my machine.</p> <p><br> In the case I receive an <code>int</code> I perform this code using <code>ntohl</code> :</p> <pre><code>int * piData = reinterpret_cast&lt;int*&gt;((void*)pData); //manage endianness of incomming network data unsigned long ulValue = ntohl(*piData); int iValue = static_cast&lt;int&gt;(ulValue); </code></pre> <p>But in the case I receive an <code>double</code>, I don't know what to do.</p> <p>The answer to the question suggest to do:</p> <pre><code>template &lt;typename T&gt; void swap_endian(T&amp; pX) { char&amp; raw = reinterpret_cast&lt;char&amp;&gt;(pX); std::reverse(&amp;raw, &amp;raw + sizeof(T)); } </code></pre> <p>However , if I quote <a href="http://forums.codeguru.com/showthread.php?298741-C-General-What-do-ntohl%28%29-and-htonl%28%29-actually-do" rel="nofollow noreferrer">this site</a>: </p> <p><code>The ntohl() function converts the unsigned integer netlong from network byte order to host byte order. When the two byte orders are different, this means the endian-ness of the data will be changed. When the two byte orders are the same, the data will not be changed.</code> </p> <p>On the contrary @GManNickG's answer to the question <strong>always does the inversion</strong> with <code>std::reverse</code> .</p> <p>Am I wrong considering that this answer is false ? ( in the extent of network management of endianess which the use of <code>ntohl</code> suggest though it was not precisely said in the title of the OP question).</p> <p>In the end: Should I split my <code>double</code> into two parts of 4 bytes and apply the <code>ntohl</code> function on the two parts ? Are there more cannonical solutions ?</p> <p>There's also this interesting question in C, <a href="https://stackoverflow.com/questions/6084279/host-to-network-double">host to network double?</a>, but it limits to 32 bits values. And the answer says doubles should be converted to strings because of architecture differences... I'm also gonna work with audio samples, should I really consider converting all the samples to strings in my database ? ( the doubles come from a database that I query over the network)</p>
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    1. COIt's not uncommon to have the way data is stored in a local database to be different than the way the data is serialized for network protocol. Is there a requirement that the data serialization be equivalent?
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    2. COCan't you combine the two solutions you linked to? `uint32_t foo = 1; if( htonl(foo) != foo ) { /* GMan's solution goes here */ } else { /* return unmodified argument */ }`. Also, the second answer is correct about floating point number representations being non-portable, even if endianness is not an issue. So should you convert to string, or use some specialized library for this? The answer depends on how portable you want this code to be.
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    3. CO@Praetorian , so I have to think about it...
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