Using this simple test program, it seems that using the operator[] for
vector access is slower than accessing through a double pointer array
access.
#include <vector>
using namespace std;
int main()
{
vector<double> v(10000);
const size_t len = v.size();
for (size_t j = 0; j < 100000; ++j)
{
double *p = &v[0];
for (size_t i = 0; i < v.size(); ++i)
v[i] = 1;
// p[i]=1;
}
}
Running using v[i] in the code above results in about 2.5 sec run time.
Running with p[i] instead of v[i] results in about 1.5 sec run time on
an amd 64. This is with gcc version 4.1 and using -O3.
I find this result suprising for such a simple data type. Is there any
way to optimize this for vector access?
Regards,
Juan
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