比较类的静态数据成员和普通数据成员哪个访问得快一点
代码
顺序访问
#include <iostream>
#include <fstream>
#include <vector>
#include <chrono>
using namespace std;
typedef chrono::microseconds UnitType;
chrono::_V2::system_clock::time_point t_start, t_end;
UnitType d;
#define TIMING_START t_start = chrono::system_clock::now();
#define TIMING_END(str) \
t_end = chrono::system_clock::now(); \
d = chrono::duration_cast<UnitType>(t_end - t_start); \
cout << str << d.count() << " us" << endl;
class A
{
public:
vector<int> nbrs;
A(size_t sz) : nbrs(sz) {}
void seq_access(int round, ostream &absorb_stdout)
{
int total = 0;
for (int i = 0; i < round; ++i)
for (size_t j = 0, jed = nbrs.size(); j < jed; ++j)
total += nbrs[j];
absorb_stdout << total;
}
};
class B
{
public:
static vector<int> nbrs;
void seq_access(int round, ostream &absorb_stdout)
{
int total = 0;
for (int i = 0; i < round; ++i)
for (size_t j = 0, jed = nbrs.size(); j < jed; ++j)
total += nbrs[j];
absorb_stdout << total;
}
};
vector<int> B::nbrs;
void compare_static_data_member(ostream &absorb_stdout)
{
const size_t sz = 100000000;
int repeat_times = 30;
B::nbrs.resize(sz);
B b;
A a(sz);
TIMING_START
a.seq_access(repeat_times, absorb_stdout);
TIMING_END("[normal data member]")
TIMING_START
b.seq_access(repeat_times, absorb_stdout);
TIMING_END("[static data member]")
}
int main()
{
ofstream absorb_stdout("tmp.txt");
compare_static_data_member(absorb_stdout);
return 0;
}
随机访问
上述seq_access改成：
void rand_access(int round, ostream &absorb_stdout)
{
int total = 0;
for (int i = 0; i < round; ++i)
for (size_t j = 0, jed = nbrs.size(), pos, max_pos = jed - 1; j < jed; ++j)
{
pos = double(rand()) / RAND_MAX * max_pos;
total += nbrs[pos];
}
absorb_stdout << total;
}
结果
顺序访问
重复30次顺序访问，nbrs元素个数100000000
不开O3：静态更快
[normal data member]10166058 us
[static data member]8635176 us
开O3：普通更快
[normal data member]831936 us
[static data member]893034 us
随机访问
100000000次随机访问nbrs
不开O3：普通更快
[normal data member]5354315 us
[static data member]5803599 us
开O3：静态略快
[normal data member]3785677 us
[static data member]3708722 us
