动态分配和随机访问:Raw、Smart、Deque、Vector.为什么生得这么快，而deque却这么慢

我创建了一个小的性能测试，比较了三种流行的动态分配技术的设置和访问时间：原始指针、std:：unique_ptr和std:：deque。

编辑：根据@NathanOliver，添加std::vector：EDIT 2：根据最新开发人员的，分配有std:：vector(n)和std:：deque(n)构造函数第3版：根据@BaummitAugen，将分配移动到计时循环中，并编译了一个优化版本。第4版：根据@PaulMcKenzie的评论，设置为2000。

结果：这些变化使事情变得更加紧张。Deque和Vector在分配和分配方面仍然较慢，而Deque在访问方面要慢得多：

pickledEgg$g++-std=c++11-o sp2-O2 sp2.cpp

Average of 2000 runs:
Method  Assign          Access
======  ======          ======
Raw:    0.0000085643    0.0000000724
Smart:  0.0000085281    0.0000000732
Deque:  0.0000205775    0.0000076908
Vector: 0.0000163492    0.0000000760

只是为了好玩，下面是-Oast结果：
pickledEgg$g++-std=c++11-o sp2-Ofast sp2.cpp

Average of 2000 runs:
Method  Assign          Access
======  ======          ======
Raw:    0.0000045316    0.0000000893
Smart:  0.0000038308    0.0000000730
Deque:  0.0000165620    0.0000076475
Vector: 0.0000063442    0.0000000699

原创：为子孙后代；注意缺少优化器-O2标志：

pickledEgg$g++-std=c++11-o sp2 sp2.cpp

Average of 100 runs:
Method  Assign      Access
======  ======      ======
Raw:    0.0000466522    0.0000468586
Smart:  0.0004391623    0.0004406758
Deque:  0.0003144142    0.0021758729
Vector: 0.0004715145    0.0003829193

更新代码：

#include <iostream>
#include <iomanip>
#include <vector>
#include <deque>
#include <chrono>
#include <memory>
const int NUM_RUNS(2000);
int main() {
std::chrono::high_resolution_clock::time_point b, e;
std::chrono::duration<double> t, raw_assign(0), raw_access(0), smart_assign(0), smart_access(0), deque_assign(0), deque_access(0), vector_assign(0), vector_access(0);
int k, tmp, n(32768);
std::cout << "Average of " << NUM_RUNS << " runs:" << std::endl; 
std::cout << "Method " << 't' << "Assign" << "tt" << "Access" << std::endl;
std::cout << "====== " << 't' << "======" << "tt" << "======" << std::endl;
// Raw
for (k=0; k<NUM_RUNS; ++k) {
b = std::chrono::high_resolution_clock::now();
int* raw_p = new int[n]; // run-time allocation
for (int i=0; i<n; ++i) { //assign
raw_p[i] = i;
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
raw_assign+=t;
b = std::chrono::high_resolution_clock::now();
for (int i=0; i<n; ++i) { //access
tmp = raw_p[i];
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
raw_access+=t;
delete [] raw_p; // :^)
}
raw_assign /= NUM_RUNS;
raw_access /= NUM_RUNS;
std::cout << "Raw:   " << 't' << std::setprecision(10) << std::fixed << raw_assign.count() << 't' << raw_access.count() << std::endl;
// Smart
for (k=0; k<NUM_RUNS; ++k) {
b = std::chrono::high_resolution_clock::now();
std::unique_ptr<int []> smart_p(new int[n]); // run-time allocation
for (int i=0; i<n; ++i) { //assign
smart_p[i] = i;
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
smart_assign+=t;
b = std::chrono::high_resolution_clock::now();
for (int i=0; i<n; ++i) { //access
tmp = smart_p[i];
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
smart_access+=t;
}
smart_assign /= NUM_RUNS;
smart_access /= NUM_RUNS;
std::cout << "Smart: " << 't' << std::setprecision(10) << std::fixed << smart_assign.count() << 't' << smart_access.count() << std::endl;
// Deque
for (k=0; k<NUM_RUNS; ++k) {
b = std::chrono::high_resolution_clock::now();
std::deque<int> myDeque(n);
for (int i=0; i<n; ++i) { //assign
myDeque[n] = i;
//          myDeque.push_back(i);
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
deque_assign+=t;
b = std::chrono::high_resolution_clock::now();
for (int i=0; i<n; ++i) { //access
tmp = myDeque[n];
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
deque_access+=t;
}
deque_assign /= NUM_RUNS;
deque_access /= NUM_RUNS;
std::cout << "Deque: " << 't' << std::setprecision(10) << std::fixed << deque_assign.count() << 't' << deque_access.count() << std::endl;
// vector
for (k=0; k<NUM_RUNS; ++k) {
b = std::chrono::high_resolution_clock::now();
std::vector<int> myVector(n);
for (int i=0; i<n; ++i) { //assign
myVector[i] = i;
//          .push_back(i);
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
vector_assign+=t;
b = std::chrono::high_resolution_clock::now();
for (int i=0; i<n; ++i) { //access
tmp = myVector[i];
//          tmp = *(myVector.begin() + i);
}
e = std::chrono::high_resolution_clock::now();
t = std::chrono::duration_cast<std::chrono::duration<double> >(e - b);
vector_access+=t;
}
vector_assign /= NUM_RUNS;
vector_access /= NUM_RUNS;
std::cout << "Vector:" << 't' << std::setprecision(10) << std::fixed << vector_assign.count() << 't' << vector_access.count() << std::endl;
std::cout << std::endl;
return 0;
}