printf more than 5 times faster than std::cout?

user_753341 0
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#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <ctime>

int main(int argc, char* argv[])
{
    std::clock_t start;
    double duration;    

    std::cout << "Starting std::cout test." << std::endl;
    start = std::clock();

    for (int i = 0; i < 1000; i++)
    {
        std::cout << "Hello, World! (" << i << ")" << std::endl;
    }

    duration = (std::clock() - start) / (double) CLOCKS_PER_SEC;

    std::cout << "Ending std::cout test." << std::endl;
    std::cout << "Time taken: " << duration << std::endl;

    std::system("pause");

    std::cout << "Starting std::printf test." << std::endl;
    start = std::clock();

    for (int i = 0; i < 1000; i++)
    {
        std::printf("Hello, World! (%i)\n", i);
        std::fflush(stdout);
    }

    duration = (std::clock() - start) / (double) CLOCKS_PER_SEC;

    std::cout << "Ending std::printf test." << std::endl;
    std::cout << "Time taken: " << duration << std::endl;

    system("pause");

    return 0;
}

Now, here are the times for the first five runs:

  • std::cout test: 1.125 s ; printf test: 0.195 s
  • std::cout test: 1.154 s ; printf test: 0.230 s
  • std::cout test: 1.142 s ; printf test: 0.216 s
  • std::cout test: 1.322 s ; printf test: 0.221 s
  • std::cout test: 1.108 s ; printf test: 0.232 s

As you can see, using printf and then fflushing takes about 5 times less time than using std::cout.

Although I did expect using std::cout's << operator to be perhaps a little slower (almost minimal) , I wasn't prepared for this huge difference. Am I making a fair test? If so, then what makes the first test so much slower than the second one, if they essentially do the exact same thing?

cout printf c++ performance
6 Answers

I only have a programming range of 1 computer, so not much testing. Anyhow, std::cout is way more faster on my build using the exact verbose code. I am using Cpp14.

I just think certain people have a pick for C++. Yes C is great language but logically I don't see how printf can be faster than std cout. Printf has to do type conversions from void pointer on runtime. Cout does that at compile time.

Admin1

I tried this test on my laptop, running Windows 10, WSL Ubuntu, CLion 2018, GCC. No optimization:

#include <iostream>
#include <cstdlib>
#include <cstdio>
#include <ctime>

int main(int argc, char *argv[]) {
    std::ios_base::sync_with_stdio(false);
    std::cin.tie(nullptr);
    std::clock_t start;
    double duration1, duration2;

    std::cout << "Starting std::cout test.\n";
    start = std::clock();

    for (int i = 0; i < 100000; i++) {
        std::cout << "Hello, World! (" << i << ")" << std::endl;
    }

    duration1 = (std::clock() - start) / (double) CLOCKS_PER_SEC;

    std::cout << "Starting std::printf test.\n";
    start = std::clock();

    for (int i = 0; i < 100000; i++) {
        std::printf("Hello, World! (%i)\n", i);
        std::fflush(stdout);
    }

    duration2 = (std::clock() - start) / (double) CLOCKS_PER_SEC;

    std::cout << "Time taken: cout " << duration1 << std::endl;
    std::cout << "Time taken Printf: " << duration2 << std::endl;

    return 0;
}

Results:

Test1: Cout: 2.25, Printf: 2.45312  (Cout run first)
Test2: Cout: 2.42188, Printf: 2.07812 (Printf Run first)
Test3: Cout: 2.26562, Printf: 2.25 (Cout run first)
Test4: Cout 2.46875, Printf: 2.57812 (Printf run first)

TL;DR: Using std::ios_base::sync_with_stdio(false) and std::cin.tie(nullptr) brings both functions to almost the same stand.

user_38318540
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