C++ 用C++计算执行时间
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calculating execution time in c++
提问by Hick
I have written a c++ program , I want to know how to calculate the time taken for execution so I won't exceed the time limit.
我写了一个c++程序，我想知道如何计算执行所花费的时间，这样我就不会超过时间限制。
#include<iostream>
using namespace std;
int main ()
{
int st[10000],d[10000],p[10000],n,k,km,r,t,ym[10000];
k=0;
km=0;
r=0;
scanf("%d",&t);
for(int y=0;y<t;y++)
{
scanf("%d",&n);
for(int i=0;i<n;i++)
{
cin>>st[i] >>d[i] >>p[i];
}
for(int i=0;i<n;i++)
{
for(int j=i+1;j<n;j++)
{
if((d[i]+st[i])<=st[j])
{
k=p[i]+p[j];
}
if(k>km)
km=k;
}
if(km>r)
r=km;
}
ym[y]=r;
}
for( int i=0;i<t;i++)
{
cout<<ym[i]<<endl;
}
//system("pause");
return 0;
}
this is my program and i want it to be within time limit 3 sec !! how to do it ? yeah sorry i meant execution time !!
这是我的程序，我希望它在 3 秒内完成！！怎么做 ？是的，对不起，我的意思是执行时间！！
回答by Ashutosh Mehra
If you have cygwin installed, from it's bash shell, run your executable, say MyProgram, using the timeutility, like so:
如果您安装了 cygwin，从它的 bash shell 运行您的可执行文件，例如MyProgram，使用该time实用程序，如下所示：
/usr/bin/time ./MyProgram
This will report how long the execution of your program took -- the output would look something like the following:
这将报告您的程序执行所用的时间——输出将类似于以下内容：
real 0m0.792s
user 0m0.046s
sys 0m0.218s
You could also manually modify your C program to instrument it using the clock()library function, like so:
您还可以手动修改 C 程序以使用clock()库函数对其进行检测，如下所示：
#include <time.h>
int main(void) {
clock_t tStart = clock();
/* Do your stuff here */
printf("Time taken: %.2fs\n", (double)(clock() - tStart)/CLOCKS_PER_SEC);
return 0;
}
回答by Sajal
With C++11 for measuring the execution time of a piece of code, we can use the now() function:
使用 C++11 来测量一段代码的执行时间，我们可以使用 now() 函数：
auto start = chrono::steady_clock::now();
// Insert the code that will be timed
auto end = chrono::steady_clock::now();
// Store the time difference between start and end
auto diff = end - start;
If you want to print the time difference between start and end in the above code, you could use:
如果要在上面的代码中打印开始和结束之间的时间差，可以使用：
cout << chrono::duration <double, milli> (diff).count() << " ms" << endl;
If you prefer to use nanoseconds, you will use:
如果您更喜欢使用纳秒，您将使用：
cout << chrono::duration <double, nano> (diff).count() << " ns" << endl;
The value of the diff variable can be also truncated to an integer value, for example, if you want the result expressed as:
diff 变量的值也可以截断为整数值，例如，如果您希望结果表示为：
diff_sec = chrono::duration_cast<chrono::nanoseconds>(diff);
cout << diff_sec.count() << endl;
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回答by Mathew Kurian
OVERVIEW
概述
I have written a simple semantic hack for this using @AshutoshMehraresponse. You code looks really readable this way!
我已经使用@AshutoshMehra响应为此编写了一个简单的语义黑客。这样你的代码看起来真的很可读！
MACRO
宏
#include <time.h>
#ifndef SYSOUT_F
#define SYSOUT_F(f, ...) _RPT1( 0, f, __VA_ARGS__ ) // For Visual studio
#endif
#ifndef speedtest__
#define speedtest__(data) for (long blockTime = NULL; (blockTime == NULL ? (blockTime = clock()) != NULL : false); SYSOUT_F(data "%.9fs", (double) (clock() - blockTime) / CLOCKS_PER_SEC))
#endif
USAGE
用法
speedtest__("Block Speed: ")
{
// The code goes here
}
OUTPUT
输出
Block Speed: 0.127000000s
回答by Alex Jenter
Note: the question was originally about compilation time, but later it turned out that the OP really meant execution time. But maybe this answer will still be useful for someone.
注意：这个问题最初是关于编译时间的，但后来发现 OP 真的意味着执行时间。但也许这个答案对某人仍然有用。
For Visual Studio: go to Tools / Options / Projects and Solutions / VC++ Project Settingsand set Build Timingoption to 'yes'. After that the time of every build will be displayed in the Output window.
对于 Visual Studio：转到Tools / Options / Projects and Solutions / VC++ Project Settings并将Build Timing选项设置为“ yes”。之后，每次构建的时间将显示在输出窗口中。
回答by pjc50
This looks like Dijstra's algorithm. In any case, the time taken to run will depend on N. If it takes more than 3 seconds there isn't any way I can see of speeding it up, as all the calculations that it is doing need to be done.
这看起来像 Dijstra 的算法。在任何情况下，运行所需的时间将取决于 N。如果它花费的时间超过 3 秒，我看不出有任何方法可以加快速度，因为它正在执行的所有计算都需要完成。
Depending on what problem you're trying to solve, there might be a faster algorithm.
根据您要解决的问题，可能有更快的算法。
回答by ejjyrex
I have used the technique said above, still I found that the time given in the Code:Blocks IDEwas more or less similar to the result obtained-(may be it will differ by little micro seconds)..
我已经使用了上面提到的技术，但我仍然发现Code:Blocks IDE 中给出的时间与获得的结果或多或少相似-（可能会相差一点微秒）。
