C/C++ 测试代码运行时间

今天在学习浙大的数据结构课程，陈越老师让我们写代码来比较迭代和递归的性能差别，遂使用了ctime or time.h中的clock函数来计算程序运行耗时。

方法

#include<ctime>

int main(){
  clock_t start, finish; // 用来保存当前时钟的变量类型
   
  start = clock(); // 调用clock函数获取当前时钟
  .....
  finish = clock(); 
   
  double duration = (double)(finish - start) / CLOCKS_PER_SEC  // CLOCKS_PER_SEC为定义在ctime中的常量
}

示例

比较递归与迭代的printN函数的性能：

#include<iostream>
#include<ctime>
#include<vector>
using namespace std;

void printN_v1(int n){
    for (int i = 1; i <= n; i++){
        cout << n;
    }
    cout << endl;
}

void printN_v2(int n){
    if (n){
        printN_v2(n-1);
        cout << n;
    }
    cout << endl;
}

int main(){
    int N[] = {10, 100, 1000, 10000}; // 测试数据 
    double duration;
    vector<double> t1;  // 迭代耗时 
    vector<double> t2;  // 递归耗时 
    
    clock_t start, finish;
    for (int i = 0; i < 4; i++){
        start = clock();
        printN_v1(N[i]);
        finish = clock();
        duration = (double)(finish - start) / CLOCKS_PER_SEC;
        t1.push_back(duration);
        
        start = clock();
        printN_v2(N[i]);
        finish = clock();
        duration = (double)(finish - start) / CLOCKS_PER_SEC;
        t2.push_back(duration);
    }
    
    cout << endl << "\tIteration \trecursion" << endl;
    for (int i = 0; i < t1.size(); i++){
        cout << N[i] << ":\t" << t1[i] << "\t\t" << t2[i] << endl;
    }
    
    return 0;
}