我做了一些长期以来一直想做的广泛测试。不妨分享一下。
这是我的双启动机i7-3770, 16GB Ram, x86_64, Windows 8.1和Ubuntu 16.04。更多信息和结论，备注如下。测试了MSVS 2017和g++(在Windows和Linux上)。
测试程序
#include <iostream>
#include <chrono>
//#include <algorithm>
#include <array>
#include <locale>
#include <vector>
#include <queue>
#include <deque>
// Note: total size of array must not exceed 0x7fffffff B = 2,147,483,647B
// which means that largest int array size is 536,870,911
// Also image size cannot be larger than 80,000,000B
constexpr int long g_size = 100000;
int g_A[g_size];
int main()
{
std::locale loc("");
std::cout.imbue(loc);
constexpr int long size = 100000; // largest array stack size
// stack allocated c array
std::chrono::steady_clock::time_point start = std::chrono::steady_clock::now();
int A[size];
for (int i = 0; i < size; i++)
A[i] = i;
auto duration = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() - start).count();
std::cout << "c-style stack array duration=" << duration / 1000.0 << "ms\n";
std::cout << "c-style stack array size=" << sizeof(A) << "B\n\n";
// global stack c array
start = std::chrono::steady_clock::now();
for (int i = 0; i < g_size; i++)
g_A[i] = i;
duration = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() - start).count();
std::cout << "global c-style stack array duration=" << duration / 1000.0 << "ms\n";
std::cout << "global c-style stack array size=" << sizeof(g_A) << "B\n\n";
// raw c array heap array
start = std::chrono::steady_clock::now();
int* AA = new int[size]; // bad_alloc() if it goes higher than 1,000,000,000
for (int i = 0; i < size; i++)
AA[i] = i;
duration = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() - start).count();
std::cout << "c-style heap array duration=" << duration / 1000.0 << "ms\n";
std::cout << "c-style heap array size=" << sizeof(AA) << "B\n\n";
delete[] AA;
// std::array<>
start = std::chrono::steady_clock::now();
std::array<int, size> AAA;
for (int i = 0; i < size; i++)
AAA[i] = i;
//std::sort(AAA.begin(), AAA.end());
duration = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() - start).count();
std::cout << "std::array duration=" << duration / 1000.0 << "ms\n";
std::cout << "std::array size=" << sizeof(AAA) << "B\n\n";
// std::vector<>
start = std::chrono::steady_clock::now();
std::vector<int> v;
for (int i = 0; i < size; i++)
v.push_back(i);
//std::sort(v.begin(), v.end());
duration = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() - start).count();
std::cout << "std::vector duration=" << duration / 1000.0 << "ms\n";
std::cout << "std::vector size=" << v.size() * sizeof(v.back()) << "B\n\n";
// std::deque<>
start = std::chrono::steady_clock::now();
std::deque<int> dq;
for (int i = 0; i < size; i++)
dq.push_back(i);
//std::sort(dq.begin(), dq.end());
duration = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() - start).count();
std::cout << "std::deque duration=" << duration / 1000.0 << "ms\n";
std::cout << "std::deque size=" << dq.size() * sizeof(dq.back()) << "B\n\n";
// std::queue<>
start = std::chrono::steady_clock::now();
std::queue<int> q;
for (int i = 0; i < size; i++)
q.push(i);
duration = std::chrono::duration_cast<std::chrono::microseconds>(std::chrono::steady_clock::now() - start).count();
std::cout << "std::queue duration=" << duration / 1000.0 << "ms\n";
std::cout << "std::queue size=" << q.size() * sizeof(q.front()) << "B\n\n";
}
结果
//////////////////////////////////////////////////////////////////////////////////////////
// with MSVS 2017:
// >> cl /std:c++14 /Wall -O2 array_bench.cpp
//
// c-style stack array duration=0.15ms
// c-style stack array size=400,000B
//
// global c-style stack array duration=0.130ms
// global c-style stack array size=400,000B
//
// c-style heap array duration=0.90ms
// c-style heap array size=4B
//
// std::array duration=0.20ms
// std::array size=400,000B
//
// std::vector duration=0.544ms
// std::vector size=400,000B
//
// std::deque duration=1.375ms
// std::deque size=400,000B
//
// std::queue duration=1.491ms
// std::queue size=400,000B
//
//////////////////////////////////////////////////////////////////////////////////////////
//
// with g++ version:
// - (tdm64-1) 5.1.0 on Windows
// - (Ubuntu 5.4.0-6ubuntu1~16.04.10) 5.4.0 20160609 on Ubuntu 16.04
// >> g++ -std=c++14 -Wall -march=native -O2 array_bench.cpp -o array_bench
//
// c-style stack array duration=0ms
// c-style stack array size=400,000B
//
// global c-style stack array duration=0.124ms
// global c-style stack array size=400,000B
//
// c-style heap array duration=0.648ms
// c-style heap array size=8B
//
// std::array duration=1ms
// std::array size=400,000B
//
// std::vector duration=0.402ms
// std::vector size=400,000B
//
// std::deque duration=0.234ms
// std::deque size=400,000B
//
// std::queue duration=0.304ms
// std::queue size=400,000
//
//////////////////////////////////////////////////////////////////////////////////////////
笔记
平均10次组装。
我最初也使用std::sort()执行测试(您可以看到它被注释掉了)，但后来删除了它们，因为没有显著的相对差异。
我的结论和评论
notice how global c-style array takes almost as much time as the heap c-style array
Out of all tests I noticed a remarkable stability in std::array's time variations between consecutive runs, while others especially std:: data structs varied wildly in comparison
O3 optimization didn't show any noteworthy time differences
Removing optimization on Windows cl (no -O2) and on g++ (Win/Linux no -O2, no -march=native) increases times SIGNIFICANTLY. Particularly for std::data structs. Overall higher times on MSVS than g++, but std::array and c-style arrays faster on Windows without optimization
g++ produces faster code than microsoft's compiler (apparently it runs faster even on Windows).
判决
当然，这是用于优化构建的代码。既然问题是关于std::vector，那么是的，它是!比普通数组(优化/未优化)慢。但是当您进行基准测试时，您自然希望生成优化的代码。
对我来说，这个节目的明星是std::array。
