Find out run time of a C/C++ program

Question

I want to find out how much time a C/C++ program takes to produce output for a certain input file.

Usually, I make an input file in txt or other format and then produce an output file in txt or any other format. For example:

int main()
{
    freopen("input.txt","r",stdin);
    freopen("output.txt","w",stdout);

    //take input and give output

    //fclose(stdin);
    //fclose(stdout);

    return 0;
}

I run the program and it shows execution time on the console window. But I am not sure that if this is the most accurate way to know the execution time.

I need to know the execution time of a program for a certain input file to set the time limit for a programming problem in some school level programming contest.

Use a [profiler](https://en.wikipedia.org/wiki/Profiling_(computer_programming)). — Captain Obvlious, Dec 30 '17 at 18:42
If you don't have a profiler std::chrono can help: http://en.cppreference.com/w/cpp/chrono Look at the example at the bottom. — drescherjm, Dec 30 '17 at 18:44
You can start a timer at the begining of your program and stop it at the end. Just save or show the time value in somewhere and check it. — Golnaz Saraji, Dec 30 '17 at 18:46
Which language, C or C++? They have different libraries for obtaining clock time and profiling. — Thomas Matthews, Dec 30 '17 at 18:46
which operating system? on linux you can just use the `time` command to give you time and memory statistics for a program. — Serge, Dec 30 '17 at 18:46
"I run the program and it shows execution time on the console window." Q: Do you run on Linux, and use the [time](https://linux.die.net/man/1/time) command? — paulsm4, Dec 30 '17 at 18:49
This answer may be of use https://stackoverflow.com/questions/44433440/how-to-check-time-performances-in-a-c-program-on-zedboard/44433887#44433887 — Galik, Dec 30 '17 at 18:59
Also what language? `C` or `C++`? (they are not the same thing, not at all) — Galik, Dec 30 '17 at 19:00

score 2 · Answer 1 · answered Dec 30 '17 at 18:48

2

On Linux you can use the time command. Write time yourexecutable On windows you can use the powershell command Measure-Command {yourexecutable}. Replace yourexecutable with the actual program binary.

answered Dec 30 '17 at 18:48

mdatsev

2,886
10
25

score 1 · Answer 2 · answered Dec 30 '17 at 18:54

1

In C you can use the time() function to measure the speed of a specific part of your program, for example:

# include <time.h>
int main() {
    /* Do stuff here */
    time_t start, finish;
    time(&start);    /* time() stores the value in the pointed buffer */
    /* Measure this part */
    time(&finish);
    printf("Part 1 took %li seconds\n", finish - start);
    /* %li may not be the good flag according to your system. */
    /* Do extra stuff here */
    return 0;
}

I have no idea how to do this in CPP...

answered Dec 30 '17 at 18:54

ft_error

132
1
6

Could anyone explain why the downvote? I don't think my answer is wrong, obviously it doesn't say how to do for CPP but others answered it. – ft_error Dec 30 '17 at 19:04
I'm guessing perhaps the downvote might have been from some C++ bigot? It seems a perfectly good answer to me... – paulsm4 Dec 31 '17 at 06:48

score 0 · Answer 3 · answered Dec 30 '17 at 18:49

Surround the code of interest in a std::chrono saving the start time and then subtract the time at the end to get the duration.

auto startTime = std::system_clock::now();
/* test code */
auto dur = std::system_clock::now() - startTime;
std::cout << "Duration: " << dur << std::endl;

You can then figure out how long to give the entry program and compare the duration against that time. Somewhat harder to forcefully abort the entry, that would pretty much require a wrapper program that launches the entries as separate processes (which is not a bad idea anyway) and if it timeout kill the process.

Find out run time of a C/C++ program

3 Answers3