iostreamは遅いという話

benchmark of 10,000,000 number's input

time ( yes 100 | ./a.out )

Optimization Flags   |     number |iostream| stdio
---------------------+------------+--------+------
CXXFLAGS=""          |        100 |  9.830 | 3.664
CXXFLAGS="-O2 -Wall" |        100 | 10.006 | 3.831
CXXFLAGS=""          | 1000000000 | 22.175 | 6.197
CXXFLAGS="-O2 -Wall" | 1000000000 | 10.835 | 6.461
#include <iostream>

using namespace std;

int main(int argc, char **argv)
{
    int a;
    for(int i = 0; i < 10000000; ++i) {
        cin >> a;
    }
    return 0;
}
#include <cstdio>

using namespace std;

int main(int argc, char **argv)
{
    int a, i;
    for(i = 0; i < 10000000; ++i) {
        scanf("%d", &a);
    }
    return 0;
}