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POC++ defensive programming: reading from a buffer with type safety
 

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    <p>Let's say I have a class that I don't own: DataBuffer. It provides various get member functions:</p> <pre><code>get(uint8_t *value); get(uint16_t *value); ... </code></pre> <p>When reading from a structure contained in this buffer, I know the order and size of fields, and I want to reduce the chance of future code changes causing an error:</p> <pre><code>struct Record { uint16_t Header; uint16_t Content; } void ReadIntoRecord(Record* r) { DataBuffer buf( initialized from the network with bytes ) buf.get(&amp;r-&gt;Header); // Good! buf.get(&amp;r-&gt;Content); } </code></pre> <p>Then someone checks in a change to do something with the header before writing it:</p> <pre><code> uint8_t customHeader; buf.get(&amp;customHeader); // Wrong, stopped reading after only 1 byte r-&gt;Header = customHeader + 1; buf.get(&amp;r-&gt;Content); // now we're reading from the wrong part of the buffer. </code></pre> <p><strong>Is the following an acceptable way to harden the code against changes? Remember, I can't change the function names to getByte, getUShort, etc. I could inherit from DataBuffer, but that seems like overkill.</strong></p> <pre><code> buf.get(static_cast&lt;uint16_t*&gt;(&amp;r-&gt;Header)); // compiler will catch incorrect variable type buf.get(static_cast&lt;uint16_t*&gt;(&amp;r-&gt;Content)) </code></pre> <p>Updated with not-eye-safe legacy code example:</p> <pre><code> float dummy_float; uint32_t dummy32; uint16_t dummy16; uint8_t dummy8; uint16_t headTypeTemp; buf.get(static_cast&lt;uint16_t*&gt;(&amp;headTypeTemp)); m_headType = HeadType(headTypeTemp); buf.get(static_cast&lt;uint8_t*&gt;(&amp;hid)); buf.get(m_Name); buf.get(m_SerialNumber); float start; buf.get(static_cast&lt;float*&gt;(&amp;start)); float stop; buf.get(static_cast&lt;float*&gt;(&amp;stop)); buf.get(static_cast&lt;float*&gt;(&amp;dummy_float)); setStuffA(dummy_float); buf.get(static_cast&lt;uint16_t*&gt;(&amp;dummy16)); setStuffB(float(dummy16)/1000); buf.get(static_cast&lt;uint8_t*&gt;(&amp;dummy8)); //reserved buf.get(static_cast&lt;uint32_t*&gt;(&amp;dummy32)); Entries().setStart( dummy32 ); buf.get(static_cast&lt;uint32_t*&gt;(&amp;dummy32)); Entries().setStop( dummy32 ); buf.get(static_cast&lt;float*&gt;(&amp;dummy_float)); Entries().setMoreStuff( dummy_float ); uint32_t datalength; buf.get(static_cast&lt;uint32_t*&gt;(&amp;datalength)); Entries().data().setLength(datalength); RetVal ret = ReturnCode::SUCCESS; Entry* data_ptr = Entries().data().data(); for (unsigned int i = 0; i &lt; datalength &amp;&amp; ret == ReturnCode::SUCCESS; i++) { ret = buf.get(static_cast&lt;float*&gt;(&amp;dummy_float)); data_ptr[i].FieldA = dummy_float; } for (unsigned int i = 0; i &lt; datalength &amp;&amp; ret == ReturnCode::SUCCESS; i++) { ret = buf.get(static_cast&lt;float*&gt;(&amp;dummy_float)); data_ptr[i].FieldB = dummy_float; } // Read in the normalization vector Util::SimpleVector&lt;float&gt; norm; buf.get(static_cast&lt;uint32_t*&gt;(&amp;datalength)); norm.setLength(datalength); for (unsigned int i=0; i&lt;datalength; i++) { norm[i] = buf.getFloat(); } setNormalization(norm); return ReturnCode::SUCCESS; } </code></pre>
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    1. USCat Zimmermann
    1. USCat Zimmermann
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      1. VTDownMod
    2. VO
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    3. VO
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    1. COno because the same guy will change the static_cast to be uint8_t ("because it was the only way to make the compiler stop complaining").
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      1. USKevin
    2. COPlease give a reason when voting down a question.
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      1. USCat Zimmermann
    3. COAFAIK, the static cast will either result in an error, or a uint16_t. So it seems like that makes your code a little more robust..at least in terms of making sure the typing is correct.
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      1. POC++ defensive programming: reading from a buffer with type safety
      1. USprelic
 

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