c++ fastest way to write vector <pair <double,double> to file -
i'm trying write lot of x/y double points file.
i came following function fastest solution, yet.
are there other ways speed process?
writing stringstream first , opening file gave nice speed boost.
bool printpoints(const vector <pair <double,double> > &points, const string &file) { if(points.empty()) return false; vector <pair <double,double> > const_iterator i; if(file != "") { stringstream ss; for(i=points.begin(); != points.end();++i ) { ss << i->first << " " << i->second << "\n"; } ofstream out(file.c_str()); if(out.fail()) { out.close(); return false; } out << ss.str(); out.close(); } return true; }
i tested this. writing stringstream buys next nothing. using file * instead of fstream give reasonable improvement.
here's test-code:
#include <vector> #include <utility> #include <fstream> #include <iostream> #include <sstream> #include <cstdio> using namespace std; bool printpoints(const vector <pair <double,double> > &points, const string &file) { if(points.empty()) return false; vector <pair <double,double> >::const_iterator i; if(file != "") { stringstream ss; for(i=points.begin(); != points.end();++i ) { ss << i->first << " " << i->second << "\n"; } ofstream out(file.c_str()); if(out.fail()) { out.close(); return false; } out << ss.str(); out.close(); } return true; } bool printpoints2(const vector <pair <double,double> > &points, const string &file) { if(points.empty()) return false; vector <pair <double,double> >:: const_iterator i; if(file != "") { ofstream out(file.c_str()); if(out.fail()) { out.close(); return false; } for(i=points.begin(); != points.end();++i ) { out << i->first << " " << i->second << "\n"; } out.close(); } return true; } bool printpoints3(const vector <pair <double,double> > &points, const string &file) { if(points.empty()) return false; vector <pair <double,double> >:: const_iterator i; if(file != "") { file *out = fopen(file.c_str(), "w"); if(!out) { return false; } for(i=points.begin(); != points.end();++i ) { fprintf(out, "%f %f", i->first, i->second); } fclose(out); } return true; } static __inline__ unsigned long long rdtsc(void) { unsigned hi, lo; __asm__ __volatile__ ("rdtsc" : "=a"(lo), "=d"(hi)); return ( (unsigned long long)lo)|( ((unsigned long long)hi)<<32 ); } int main() { vector <pair <double,double> > v; unsigned long long t1, t2; for(int = 1; <= 10000000; i++) { v.push_back(make_pair<double, double>((double)i, 1.0/i)); } t1 = rdtsc(); printpoints(v, "points.txt"); t2 = rdtsc(); cout << "time = " << t2 - t1 << endl; t1 = rdtsc(); printpoints2(v, "points2.txt"); t2 = rdtsc(); cout << "time = " << t2 - t1 << endl; t1 = rdtsc(); printpoints3(v, "points3.txt"); t2 = rdtsc(); cout << "time = " << t2 - t1 << endl; } results: time = 55363637480 time = 54413392112 time = 33069402767 obviously, results may vary depending on processor type, memory type, hard disk system (or network drive storage), etc, etc. i've tested in past, , found similar results.
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