Hi,
I was interested in the efficiacy of std::vector.
Using the test program below, I receive the following results.
The "simple" handling is equivalent with the C array access.
The [] and iterator access time of the vector element
is an order of magnitude worse, than that of the simple access.
This is not because of index limit control, it is done by at()
and its use increases that access time by a factor of three.
What is going on in the background here, that the implementation
is so ineffective?
( I did my tests with WinXP/cygwin/g++/time,
using different setting of the #define-s at the beginning)
Shall I expect similar ineffectivity with the other STL objects?
Regards
Janos
Empty cycle
real 0m2.173s
user 0m1.892s
sys 0m0.080s
STL=1, SIMPLE=1, size=0
real 0m4.917s
user 0m4.646s
sys 0m0.070s
STL=1, size=0
real 0m33.939s
user 0m33.658s
sys 0m0.090s
STL=1, ITERATOR=1, size=1000
real 0m34.059s
user 0m33.688s
sys 0m0.100s
STL=1, AT=1, size=1000
real 1m22.769s
user 1m22.368s
sys 0m0.090s
#define STL 1
#define SIMPLE 0
#define ITERATOR 1
#define AT 0
#define EMPTY 1
#if STL
#include <vector>
#endif
using namespace std;
#include <iostream>
#define ARR_SIZE 1000
#define CYCLES 1000000
main (int argc, char** argv)
{
long int i,j,*P;
#if EMPTY
cout << "Empty cycle";
#else
#if STL
#if ITERATOR || AT
std::vector<long int>::iterator pos;
std::vector<long int> arr(ARR_SIZE);
#else
std::vector <long int> arr;
arr.reserve(ARR_SIZE);
#endif
cout << "STL=1";
#if SIMPLE
cout << ", SIMPLE=1";
#endif
#if ITERATOR
cout << ", ITERATOR=1";
#endif
#if AT
cout << ", AT=1";
#endif
cout << ", size=" << arr.size();
#else
long int *arr;
arr = new long int[ARR_SIZE];
cout << "STL=0";
#endif
#endif
cout << endl;
#if SIMPLE && STL
P = &arr[0];
#endif
for(j=0;j