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Message: [QUOTE="Alex Gerdemann, post: 1513704"] Hello, I have spent a bunch of time converting a Java program I wrote to C++ in order to improve performance, and have found that it is not necessarily faster. Specifically, I'm writing a circuit simulator, so I must first parse the netlist file. The program goes through an input file, and makes a hash_set of unique nodes (std::string's). The words are then sorted and numbered by copying the hash_set into a vector and sorting. Then, I run a series of binary searches on the vector to allocate lines in a matrix for each element. I've modified STL's lower_bound() to my getIndex() which functions like Java's equivalent by returning negative indices when the element is not found. Also, Java provides a HashSet class that can hash any kind of element it may contain. Since, the STL only hashes selected items I had to convert my std::strings to const char*'s for hashing. Other than that, my code in the Java and C++ is quite similar. However, the parse of a 100k line file took around a second for Java, but more like 17s for C++ . In fact, using std::set instead of hash_set actually improved performance to about 15s in C++. Any idea why there would be such a difference? In particular, I suspect that my hash function may be slow from the call to c_str(). Does this have to allocate new memory or just point to somewhere inside the object? I'm kind of curious what Java actually uses for its hash. Any general performace/other criticisms on my scheme are certainly welcome. On the plus side there is a great direct sparse linear solver for C. I've only been able to find a iterative sparse solver for Java. This makes the C++ code overall much faster than Java, but I suspect that the parse stage should run at least as fast or faster. Thanks, Alex Gerdemann University of Illinois at Urbana-Champaign For reference, I've included a sketch of the code So I did something like the following: struct hashSet { __gnu_css::hash<const char*> h; bool operator()(std::string& s) const { return h(s.ctr()); } }; inline int getIndex(const std::vector<std::string>& list, const std::string& item) { std::vector<std::string>::const_iterator i = std::lower_bound(list.begin(), list.end(), item); if(i==list.end()) { return -(static_cast<int>(i-list.begin())+1); } else if(*i != item) { return -(static_cast<int>(i-list.begin())+1); } return static_cast<int>(i-list.begin()); } __gnu_cxx::hash_set<std::string, hashString> nodeSet; std::vector<std::string> nodeVector; while(!done) { //read a line of file //split the line into words and push into a vector //check for syntax errors nextNode = some word in line; nodeSet.insert(nextNode); } std::copy(nodeSet.begin(),node.end(),std::back_inserter(nodeVector)); std::sort(nodeVector.begin(),nodeVector.end()); while(!done) { //read line from previously stored words //more error checking thisNode = some word in line getIndex(nodeVector, thisNode); //allocate an object representing element containing proper indices representing nodes //push pointer to element into a vector } [/QUOTE]

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