程序执行时间

Question

Is there a software/website where I can submit my C, C++ and Java codes and get statistics like the program execution time, memory used ? I'm interested in doing a comparision of the same code in different languages and getting an estimate of which data structures/operations are better suited for which language.

Answer 1

Do it yourself. On a *nix machine (eg Linux and OSX) just run from the terminal:

time java YourJavaProgram

or

time ./YourCProgram

On Windows, you can write a little batch script to do the equivalent.

Answer 2

您可以将程序粘贴到ideone ，它将告诉您执行时间和内存消耗。

Answer 3

The total used / free memory of an program can be obtained in the program via java.lang.Runtime.getRuntime();

The runtime has several method which relates to the memory. The following coding example demonstrate its usage.

package test;

import java.util.ArrayList;
import java.util.List;

public class PerformanceTest {
  private static final long MEGABYTE = 1024L * 1024L;

  public static long bytesToMegabytes(long bytes) {
    return bytes / MEGABYTE;
  }

  public static void main(String[] args) {
    // I assume you will know how to create a object Person yourself...
    List<Person> list = new ArrayList<Person>();
    for (int i = 0; i <= 100000; i++) {
      list.add(new Person("Jim", "Knopf"));
    }
    // Get the Java runtime
    Runtime runtime = Runtime.getRuntime();
    // Run the garbage collector
    runtime.gc();
    // Calculate the used memory
    long memory = runtime.totalMemory() - runtime.freeMemory();
    System.out.println("Used memory is bytes: " + memory);
    System.out.println("Used memory is megabytes: "
        + bytesToMegabytes(memory));
  }
} 

Use System.currentTimeMillis() to get the start time and the end time and calculate the difference.

package performance.test;

class TimeTest1 {
  public static void main(String[] args) {

    long startTime = System.currentTimeMillis();

    long total = 0;
    for (int i = 0; i < 10000000; i++) {
      total += i;
    }

    long stopTime = System.currentTimeMillis();
    long elapsedTime = stopTime - startTime;
    System.out.println(elapsedTime);
  }
} 

Answer 4

That's called benchmarking and you can do it yourself. The thing is that many other variables affect the results, so it would be best to control the environment and measure the performance of your program trying to eliminate as much external variables as possible.

For example, it is advisable to do all the measurements of all the programs on the same machine, with the same environment, as much as that can be achievable.

Answer 5

if you want to get benchmark of functions, using "time" is not fair. You should write following in your language.

time_before = get_now()
// do something
span = get_time() - time_before