因為empty的效率比size()高。

#include <iostream>

#include <vector>

#include "time.h"

using namespace std;

typedef vector<int> VI;

template<class T>

T push_int_containers(int large, int small, T c)

{

? ? for (int i = large; i>small ; i--)

? ? {

? ? ? ? c.push_back(i);

? ? }

? ? return c;

}?

template<class T>

void print_containers(string name,T c)

{

? ? cout << "\n" << name <<" : ";

? ? for (auto i = c.begin(); i != c.end(); ++i)

? ? {

? ? ? ? cout << *i << " ";

? ? }

? ? cout << "\n";

}

int main()

{

? ? VI v1;

? ? v1 = push_int_containers(100,1,v1);

? ??

? ? auto b1 = clock();

? ? cout << (v1.size() == 0) << "\n";

? ? auto e1 = clock();

? ? cout << "the time of (v1.size() == 0) is " << e1 - b1 << "\n";

? ??

? ? auto b2 = clock();

? ? cout << (v1.empty() == true) << "\n";

? ? auto e2 = clock();

? ? cout << "the time of (v1.empty() == true) is " << e2 - b2 << "\n";

? ??

? ? return 0;

}

輸出結(jié)果：

0

the time of (v1.size() == 0) is 31

0

the time of (v1.empty() == true) is 2

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