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POConvert an number with arbitrary length from decimal to hex in c++
 

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  1. POConvert an number with arbitrary length from decimal to hex in c++
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    <p>I've seen several examples for converting a number from decimal to hex (or base 10 to base 16), but I have a few restrictions for what I'm trying to do. I need to be able to convert a string with a decimal number into another string as a hex number. The number is potentially too big to fit inside of any primitive data types - ie: can't use ints, unsigned ints, doubles, etc...</p> <p>This should be able to perform the same calculations as listed on this page. <a href="http://www.kaagaard.dk/service/convert.htm" rel="nofollow">http://www.kaagaard.dk/service/convert.htm</a></p> <p>I've tried this, but it hasn't worked for me.</p> <p>The call to the function:</p> <pre><code>const int maxLen = 256; char destination[maxLen]; int retVal = convertBase(destination, maxLen, "123487032174829820348320429437483266812812"); </code></pre> <p>The function definition:</p> <pre><code>int convertBase(char* dest, int maxDestLength, const char* inputInBase10) { const char lookUpTable[] = { "0123456789abcdef" }; const std::string input = inputInBase10; const unsigned int inputSize = input.length(); std::string output; output.reserve(2 * inputSize); for(unsigned int i = 0; i &lt; inputSize; ++i) { const unsigned char c = input[i]; output.push_back(lookUpTable[c &gt;&gt; 4]); output.push_back(lookUpTable[c &amp; 15]); } if(output.length() &lt; maxDestLength) strcpy_s(dest, output.length(), output.c_str()); else strcpy_s(dest, maxDestLength, output.c_str()); cout &lt;&lt; dest &lt;&lt; endl; return strlen(dest); } </code></pre> <p>The expected hex number: "16ae5514d07e120126dfbcb3073fddb2b8c"</p> <p>The actual hex number generated: "313233343837303332313734383239383230333438333230343239343337343833323636383132383132"</p> <p>Also, I keep getting an error that the buffer is too small when passing back into a char* (repeated below)</p> <pre><code> if(output.length() &lt; maxDestLength) strcpy_s(dest, output.length(), output.c_str()); else strcpy_s(dest, maxDestLength, output.c_str()); </code></pre>
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    1. USrkeller
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      1. POConvert an number with arbitrary length from decimal to hex in c++
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      1. VTUpMod
    1. COYou're converting the ASCII values of the digits in the input string to hex, not the actual number represented by the input string.
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      1. POConvert an number with arbitrary length from decimal to hex in c++
      1. USJonathan Potter
    2. COHere's a hint: the output you're getting ("313233343837") looks like the ASCII values (encoded in the string as hex bytes) of the characters of your input number - e.g. 0x38 == '8'
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      1. USMatt Curtis
    3. COGenerally you need to do long division for this kind of thing, but when you don't have long division, you can build it up with a series of additions. Does this have to be optimal? I have a non-optimal but simple solution.
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      1. POConvert an number with arbitrary length from decimal to hex in c++
      1. USpaddy
 

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