timing a function call as if-statement condition in cpp

Question

I have a function and sometimes it gets called as a condition in if-statements, and I am interested to time exactly these calls.

I wonder if there is any way to do something like this for timing it in cpp:

using watch = std::chrono::high_resolution_clock;
std::chrono::nanoseconds time(0);
if ( auto start = watch::now(); SOME_FUNCTION(); auto end = watch::now();)
{...}else{...}
time += (end - start);

Answer 1

You can write a function that wraps the function you already have:

#include <iostream>
#include <chrono>

using watch = std::chrono::high_resolution_clock;

template <class F>
auto measure_time(const F& f, std::chrono::nanoseconds& time) -> decltype(f()) {
    auto start = watch::now();
    auto return_value = f();
    auto end = watch::now();
    time += end - start;
    return return_value;
}

Simple exercise:

bool some_function() {
    return true;
}

int main() {
    std::chrono::nanoseconds time(0);

    if (measure_time(some_function, time)) {
        std::cout << "Yea\n";
    } else {
        std::cout << "Nay\n";
    }
}

You can also wrap a function that takes arguments. This is simple to do with a lambda expression:

void* some_other_function(void* v) {
    return v;
}

int main() {
    std::chrono::nanoseconds time(0);

    if (measure_time([]{ return some_other_function(0); }, time)) {
        std::cout << "Yea\n";
    } else {
        std::cout << "Nay\n";
    }
}