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POChar* vs String Speed in C++
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  1. POChar* vs String Speed in C++
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    copied!<p>I have a C++ program that will read in data from a binary file and originally I stored data in <code>std::vector&lt;char*&gt; data</code>. I have changed my code so that I am now using strings instead of char*, so that <code>std::vector&lt;std::string&gt; data</code>. Some changes I had to make was to change from <code>strcmp</code> to <code>compare</code> for example. </p> <p>However I have seen my execution time dramatically increase. For a sample file, when I used char* it took 0.38s and after the conversion to string it took 1.72s on my Linux machine. I observed a similar problem on my Windows machine with execution time increasing from 0.59s to 1.05s. </p> <p>I believe this function is causing the slow down. It is part of the converter class, note private variables designated with<code>_</code> at the end of variable name. I clearly am having memory problems here and stuck in between C and C++ code. <em>I want this to be C++ code, so I updated the code at the bottom.</em></p> <p>I access <code>ids_</code> and <code>names_</code> many times in another function too, so access speed is very important. <strong>Through the use of creating a <code>map</code> instead of two separate vectors, I have been able to achieve faster speeds with more stable C++ code. Thanks to everyone!</strong></p> <h2>Example NewList.Txt</h2> <pre><code>2515 ABC 23.5 32 -99 1875.7 1 1676 XYZ 12.5 31 -97 530.82 2 279 FOO 45.5 31 -96 530.8 3 </code></pre> <h2>OLD Code:</h2> <pre><code>void converter::updateNewList(){ FILE* NewList; char lineBuffer[100]; char* id = 0; char* name = 0; int l = 0; int n; NewList = fopen("NewList.txt","r"); if (NewList == NULL){ std::cerr &lt;&lt; "Error in reading NewList.txt\n"; exit(EXIT_FAILURE); } while(!feof(NewList)){ fgets (lineBuffer , 100 , NewList); // Read line l = 0; while (!isspace(lineBuffer[l])){ l = l + 1; } id = new char[l]; switch (l){ case 1: n = sprintf (id, "%c", lineBuffer[0]); break; case 2: n = sprintf (id, "%c%c", lineBuffer[0], lineBuffer[1]); break; case 3: n = sprintf (id, "%c%c%c", lineBuffer[0], lineBuffer[1], lineBuffer[2]); break; case 4: n = sprintf (id, "%c%c%c%c", lineBuffer[0], lineBuffer[1], lineBuffer[2],lineBuffer[3]); break; default: n = -1; break; } if (n &lt; 0){ std::cerr &lt;&lt; "Error in processing ids from NewList.txt\n"; exit(EXIT_FAILURE); } l = l + 1; int s = l; while (!isspace(lineBuffer[l])){ l = l + 1; } name = new char[l-s]; switch (l-s){ case 2: n = sprintf (name, "%c%c", lineBuffer[s+0], lineBuffer[s+1]); break; case 3: n = sprintf (name, "%c%c%c", lineBuffer[s+0], lineBuffer[s+1], lineBuffer[s+2]); break; case 4: n = sprintf (name, "%c%c%c%c", lineBuffer[s+0], lineBuffer[s+1], lineBuffer[s+2],lineBuffer[s+3]); break; default: n = -1; break; } if (n &lt; 0){ std::cerr &lt;&lt; "Error in processing short name from NewList.txt\n"; exit(EXIT_FAILURE); } ids_.push_back ( std::string(id) ); names_.push_back(std::string(name)); } bool isFound = false; for (unsigned int i = 0; i &lt; siteNames_.size(); i ++) { isFound = false; for (unsigned int j = 0; j &lt; names_.size(); j ++) { if (siteNames_[i].compare(names_[j]) == 0){ isFound = true; } } } fclose(NewList); delete [] id; delete [] name; } </code></pre> <h2>C++ CODE</h2> <pre><code>void converter::updateNewList(){ std::ifstream NewList ("NewList.txt"); while(NewList.good()){ unsigned int id (0); std::string name; // get the ID and name NewList &gt;&gt; id &gt;&gt; name; // ignore the rest of the line NewList.ignore( std::numeric_limits&lt;std::streamsize&gt;::max(), '\n'); info_.insert(std::pair&lt;std::string, unsigned int&gt;(name,id)); } NewList.close(); } </code></pre> <p>UPDATE: Follow up question: <a href="https://stackoverflow.com/q/3992548/363829">Bottleneck from comparing strings</a> and thanks for the very useful help! I will not be making these mistakes in the future!</p>
 

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