#include "CycleTimeTst.h"
#include <string>
#include <vector>
#include <list>
#include <limits>
#include <assert.h>
#include <QTime>
#include <QDebug>class TimeUsedGuard
{
public:
TimeUsedGuard(const std::string& msg)
: m_msg(msg)
, m_time(QTime::currentTime())
{
}
~TimeUsedGuard()
{
qDebug() << m_msg.c_str() << "use time:" << m_time.elapsed() << "ms";
}private:
std::string m_msg;
QTime m_time;
};template <typename T>
T useData(T val)
{
return std::sqrt(val);
}
template <typename _Container>
void normalForLoop(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
size_t i = 0;
for (; i < datas.size(); ++i)
{
useData(datas[i]);
}
}
template <typename _Container>
void normalForLoopCallSizeOnce(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
size_t i = 0;
size_t size = datas.size();
for (; i < size; ++i)
{
useData(datas[i]);
}
}
template <typename _Container>
void iterator(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
auto pos = datas.cbegin();
for (; pos != datas.cend(); ++pos)
{
useData(*pos);
}
}
template <typename _Container>
void iteratorCallCEndOnce(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
auto pos = datas.cbegin();
auto end = datas.cend();
for (; pos != end; ++pos)
{
useData(*pos);
}
}
template <typename _Container>
void qtForeach(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
foreach (auto data, datas)
{
useData(data);
}
}
template <typename _Container>
void stdForeach(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
std::for_each(datas.cbegin(), datas.cend(), useData<typename _Container::value_type>);
}
template <typename _Container>
void rangeForLoop(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
for (auto data : datas)
{
useData(data);
}
}
template <typename _Container>
void rangeForLoopReference(const _Container& datas)
{
TimeUsedGuard timeUsedGuard(__FUNCTION__);
for (auto& data : datas)
{
useData(data);
}
}
class CycleTimeTst
{
public:
CycleTimeTst();
};
CycleTimeTst g_CycleTimeTst;
CycleTimeTst::CycleTimeTst()
{
constexpr unsigned long MAX_AMOUNT = 100 * 1000 * 1000; // std::vector<int> datas;
// for (unsigned long i = 1; i < MAX_AMOUNT; ++i)
// {
// datas.push_back(i);
// }
std::list<double> datas;
double d = 1.0;
for (unsigned long i = 1; i < MAX_AMOUNT / 10; ++i)
{
datas.push_back(d);
} // normalForLoop(datas);
// normalForLoopCallSizeOnce(datas);
iterator(datas);
iteratorCallCEndOnce(datas);
qtForeach(datas);
stdForeach(datas);
rangeForLoop(datas);
rangeForLoopReference(datas);
// vector<int> 100 * 1000 * 1000 times, debug & release:
// normalForLoop use time: 1096 ms normalForLoop use time: 113 ms
// normalForLoopCallSizeOnce use time: 926 ms normalForLoopCallSizeOnce use time: 106 ms
// iterator use time: 1941 ms iterator use time: 103 ms
// iteratorCallCEndOnce use time: 1473 ms iteratorCallCEndOnce use time: 101 ms
// qtForeach use time: 1846 ms qtForeach use time: 262 ms
// stdForeach use time: 1488 ms stdForeach use time: 120 ms
// rangeForLoop use time: 1527 ms rangeForLoop use time: 101 ms
// rangeForLoopReference use time: 1551 ms rangeForLoopReference use time: 102 ms // list<double> 10 * 1000 * 1000 times, debug & release:
// iterator use time: 206 ms iterator use time: 27 ms
// iteratorCallCEndOnce use time: 183 ms iteratorCallCEndOnce use time: 26 ms
// qtForeach use time: 1493 ms qtForeach use time: 743 ms
// stdForeach use time: 182 ms stdForeach use time: 27 ms
// rangeForLoop use time: 186 ms rangeForLoop use time: 26 ms
// rangeForLoopReference use time: 186 ms rangeForLoopReference use time: 27 ms
}

结论区

个人总结:
vector支持随机访问,但无通用性,当采用list后,就不能再使用了,不可取.
迭代器与范围for循环所用时间无明显差异, qt提供的foreach显然是最差的方法, std算法for_each也还可以接受, 但范围for循环好看得多, 更好用啊!
在循环中调用调用cend方法,会频繁创建一个新的迭代器(不停的构造与析构),另外还有函数调用开销,在debug版本结果来看似乎确实有一定的影响,但在realease版本下所花时间几乎相等,也许编译器有优化吧!

摘自
https://www.cnblogs.com/diysoul/p/7096795.html
阿Hai C++11中对容器的各种循环遍历的效率比较