C++ std::vector 三种遍历方式的效率比较

#include <iostream>
#include <vector>
#include <stdint.h>
#include <ctime>

int main()
{
    const uint32_t loop = 1000000;
    std::vector<int32_t> vec;
    clock_t timeStart = 0;
    for (uint32_t i = 0; i < loop; ++i)
    {
        vec.push_back(i);
    }
    // test time use
    // 1.by index
    timeStart = clock();
    for (uint32_t i = 0; i < vec.size(); ++i)
    {
        vec[i];
    }
    std::cout << clock() - timeStart << "ms" << std::endl;
    // 2.by iterator
    timeStart = clock();
    for (std::vector<int32_t>::const_iterator it = vec.begin(); it != vec.end(); ++it)
    {
        *it;
    }
    std::cout << clock() - timeStart << "ms" << std::endl;
    // 3.by auto iterator
    timeStart = clock();
    for (auto it = vec.begin(); it != vec.end(); ++it)
    {
        *it;
    }
    std::cout << clock() - timeStart << "ms" << std::endl;
    getchar();
    return 0;
}