In reference to the thread on
http://cboard.cprogramming.com/showthread.php?t=109567
and this old thread:
http://cboard.cprogramming.com/showthread.php?t=104334
I have updated the code to use dynamic memory allocation for the array model.
Here is the code I used (generally unmodified from previous test, aside from adding extra code to do the dynamic memory allocation):
Key:Code:#include <iostream>
#include <iomanip>
#include <vector>
#include <ctime>
const int size = 128;
class B
{
public:
virtual int sum() = 0;
virtual ~B() {}
};
class V : public B
{
private:
std::vector < std::vector <int> > vec;
public:
V()
{
for(int i = 0; i < size; i++)
{
vec.push_back(std::vector<int>(0));
for(int j = 0; j < size; j++)
{
vec[i].push_back(i * j);
}
}
}
virtual int sum() {
int s = 0;
for(int i = 0; i < size; i++)
for(int j = 0; j < size; j++)
s += vec[i][j];
return s;
}
};
class A : public B
{
private:
int arr[size][size];
public:
A()
{
for(int i = 0; i < size; i++)
{
for(int j = 0; j < size; j++)
{
arr[i][j] = i * j;
}
}
}
int sum() {
int s = 0;
for(int i = 0; i < size; i++)
for(int j = 0; j < size; j++)
s += arr[i][j];
return s;
}
};
class D: public B
{
private:
int **parr;
public:
D()
{
parr = new int*[size];
for(int i = 0; i < size; i++)
{
parr[i] = new int[size];
for(int j = 0; j < size; j++)
{
parr[i][j] = i * j;
}
}
}
~D()
{
for(int i = 0; i < size; i++)
{
delete [] parr[i];
}
delete [] parr;
}
int sum() {
int s = 0;
for(int i = 0; i < size; i++)
for(int j = 0; j < size; j++)
s += parr[i][j];
return s;
}
};
int func(B *b)
{
return b->sum();
}
void timeIt(char *name, int (*f)(B *b), B * b)
{
int x = 0;
clock_t t = clock();
for(int i = 0; i < 1000000; i++)
{
x += f(b);
}
t = clock() - t;
std::cout << "x = " << x << std::endl;
std::cout << name << ": " << std::setprecision(6) << static_cast<double>(t) / CLOCKS_PER_SEC << std::endl;
}
#define TIME_IT(f, b) do { timeIt(#b, f, &b); } while(0)
int main()
{
A a;
V v;
D d;
TIME_IT(func, a);
TIME_IT(func, v);
TIME_IT(func, d);
}
a - fixed size array on the stack.
v - vector of vector.
d - dynamically allocated 2D array.
Result: g++ -O2 -fomit-frame-pointer -funroll-loops
Result: Visual Studio .Net (VC++ version 7.0, cl version 13.00)Code:x = -802947072
a: 12.031
x = -802947072
v: 11.297
x = -802947072
d: 12.907
As you can see (and as I expected), the dynamic variant ends up closer to vector, but still slightly slower than the fixed size array.Code:x = -802947072
a: 6.218
x = -802947072
v: 10.75
x = -802947072
d: 7.891
--
Mats
