I want to find out how much time a certain function takes in my C++ program to execute on Linux. Afterwards, I want to make a speed comparison . I saw several time function but ended up with this from boost. Chrono:
process_user_cpu_clock, captures user-CPU time spent by the current process
Now, I am not clear if I use the above function, will I get the only time which CPU spent on that function?
Secondly, I could not find any example of using the above function. Can any one please help me how to use the above function?
P.S: Right now , I am using std::chrono::system_clock::now() to get time in seconds but this gives me different results due to different CPU load every time.
It is a very easy-to-use method in C++11. You have to use std::chrono::high_resolution_clock from <chrono> header.
Use it like so:
#include <chrono>
/* Only needed for the sake of this example. */
#include <iostream>
#include <thread>
void long_operation()
{
/* Simulating a long, heavy operation. */
using namespace std::chrono_literals;
std::this_thread::sleep_for(150ms);
}
int main()
{
using std::chrono::high_resolution_clock;
using std::chrono::duration_cast;
using std::chrono::duration;
using std::chrono::milliseconds;
auto t1 = high_resolution_clock::now();
long_operation();
auto t2 = high_resolution_clock::now();
/* Getting number of milliseconds as an integer. */
auto ms_int = duration_cast<milliseconds>(t2 - t1);
/* Getting number of milliseconds as a double. */
duration<double, std::milli> ms_double = t2 - t1;
std::cout << ms_int.count() << "ms\n";
std::cout << ms_double.count() << "ms\n";
return 0;
}
This will measure the duration of the function long_operation.
Possible output:
150ms
150.068ms
Working example: https://godbolt.org/z/oe5cMd
Here's a function that will measure the execution time of any function passed as argument:
#include <chrono>
#include <utility>
typedef std::chrono::high_resolution_clock::time_point TimeVar;
#define duration(a) std::chrono::duration_cast<std::chrono::nanoseconds>(a).count()
#define timeNow() std::chrono::high_resolution_clock::now()
template<typename F, typename... Args>
double funcTime(F func, Args&&... args){
TimeVar t1=timeNow();
func(std::forward<Args>(args)...);
return duration(timeNow()-t1);
}
Example usage:
#include <iostream>
#include <algorithm>
typedef std::string String;
//first test function doing something
int countCharInString(String s, char delim){
int count=0;
String::size_type pos = s.find_first_of(delim);
while ((pos = s.find_first_of(delim, pos)) != String::npos){
count++;pos++;
}
return count;
}
//second test function doing the same thing in different way
int countWithAlgorithm(String s, char delim){
return std::count(s.begin(),s.end(),delim);
}
int main(){
std::cout<<"norm: "<<funcTime(countCharInString,"precision=10",'=')<<"\n";
std::cout<<"algo: "<<funcTime(countWithAlgorithm,"precision=10",'=');
return 0;
}
Output:
norm: 15555
algo: 2976
In Scott Meyers book I found an example of universal generic lambda expression that can be used to measure function execution time. (C++14)
auto timeFuncInvocation =
[](auto&& func, auto&&... params) {
// get time before function invocation
const auto& start = std::chrono::high_resolution_clock::now();
// function invocation using perfect forwarding
std::forward<decltype(func)>(func)(std::forward<decltype(params)>(params)...);
// get time after function invocation
const auto& stop = std::chrono::high_resolution_clock::now();
return stop - start;
};
The problem is that you are measure only one execution so the results can be very differ. To get a reliable result you should measure a large number of execution.
According to Andrei Alexandrescu lecture at code::dive 2015 conference - Writing Fast Code I:
Measured time: tm = t + tq + tn + to
where:
tm - measured (observed) time
t - the actual time of interest
tq - time added by quantization noise
tn - time added by various sources of noise
to - overhead time (measuring, looping, calling functions)
According to what he said later in the lecture, you should take a minimum of this large number of execution as your result.
I encourage you to look at the lecture in which he explains why.
Also there is a very good library from google - https://github.com/google/benchmark.
This library is very simple to use and powerful. You can checkout some lectures of Chandler Carruth on youtube where he is using this library in practice. For example CppCon 2017: Chandler Carruth “Going Nowhere Faster”;
Example usage:
#include <iostream>
#include <chrono>
#include <vector>
auto timeFuncInvocation =
[](auto&& func, auto&&... params) {
// get time before function invocation
const auto& start = high_resolution_clock::now();
// function invocation using perfect forwarding
for(auto i = 0; i < 100000/*largeNumber*/; ++i) {
std::forward<decltype(func)>(func)(std::forward<decltype(params)>(params)...);
}
// get time after function invocation
const auto& stop = high_resolution_clock::now();
return (stop - start)/100000/*largeNumber*/;
};
void f(std::vector<int>& vec) {
vec.push_back(1);
}
void f2(std::vector<int>& vec) {
vec.emplace_back(1);
}
int main()
{
std::vector<int> vec;
std::vector<int> vec2;
std::cout << timeFuncInvocation(f, vec).count() << std::endl;
std::cout << timeFuncInvocation(f2, vec2).count() << std::endl;
std::vector<int> vec3;
vec3.reserve(100000);
std::vector<int> vec4;
vec4.reserve(100000);
std::cout << timeFuncInvocation(f, vec3).count() << std::endl;
std::cout << timeFuncInvocation(f2, vec4).count() << std::endl;
return 0;
}
EDIT:
Ofcourse you always need to remember that your compiler can optimize something out or not. Tools like perf can be useful in such cases.
simple program to find a function execution time taken.
#include <iostream>
#include <ctime> // time_t
#include <cstdio>
void function()
{
for(long int i=0;i<1000000000;i++)
{
// do nothing
}
}
int main()
{
time_t begin,end; // time_t is a datatype to store time values.
time (&begin); // note time before execution
function();
time (&end); // note time after execution
double difference = difftime (end,begin);
printf ("time taken for function() %.2lf seconds.\n", difference );
return 0;
}
Easy way for older C++, or C:
#include <time.h> // includes clock_t and CLOCKS_PER_SEC
int main() {
clock_t start, end;
start = clock();
// ...code to measure...
end = clock();
double duration_sec = double(end-start)/CLOCKS_PER_SEC;
return 0;
}
Timing precision in seconds is 1.0/CLOCKS_PER_SEC
#include <iostream>
#include <chrono>
void function()
{
// code here;
}
int main()
{
auto t1 = std::chrono::high_resolution_clock::now();
function();
auto t2 = std::chrono::high_resolution_clock::now();
auto duration = std::chrono::duration_cast<std::chrono::microseconds>( t2 - t1 ).count();
std::cout << duration<<"/n";
return 0;
}
This Worked for me.
Note:
The high_resolution_clock is not implemented consistently across different standard library implementations, and its use should be avoided. It is often just an alias for std::chrono::steady_clock or std::chrono::system_clock, but which one it is depends on the library or configuration. When it is a system_clock, it is not monotonic (e.g., the time can go backwards).
For example, for gcc's libstdc++ it is system_clock, for MSVC it is steady_clock, and for clang's libc++ it depends on configuration.
Generally one should just use std::chrono::steady_clock or std::chrono::system_clock directly instead of std::chrono::high_resolution_clock: use steady_clock for duration measurements, and system_clock for wall-clock time.
Here is an excellent header only class template to measure the elapsed time of a function or any code block:
#ifndef EXECUTION_TIMER_H
#define EXECUTION_TIMER_H
template<class Resolution = std::chrono::milliseconds>
class ExecutionTimer {
public:
using Clock = std::conditional_t<std::chrono::high_resolution_clock::is_steady,
std::chrono::high_resolution_clock,
std::chrono::steady_clock>;
private:
const Clock::time_point mStart = Clock::now();
public:
ExecutionTimer() = default;
~ExecutionTimer() {
const auto end = Clock::now();
std::ostringstream strStream;
strStream << "Destructor Elapsed: "
<< std::chrono::duration_cast<Resolution>( end - mStart ).count()
<< std::endl;
std::cout << strStream.str() << std::endl;
}
inline void stop() {
const auto end = Clock::now();
std::ostringstream strStream;
strStream << "Stop Elapsed: "
<< std::chrono::duration_cast<Resolution>(end - mStart).count()
<< std::endl;
std::cout << strStream.str() << std::endl;
}
}; // ExecutionTimer
#endif // EXECUTION_TIMER_H
Here are some uses of it:
int main() {
{ // empty scope to display ExecutionTimer's destructor's message
// displayed in milliseconds
ExecutionTimer<std::chrono::milliseconds> timer;
// function or code block here
timer.stop();
}
{ // same as above
ExecutionTimer<std::chrono::microseconds> timer;
// code block here...
timer.stop();
}
{ // same as above
ExecutionTimer<std::chrono::nanoseconds> timer;
// code block here...
timer.stop();
}
{ // same as above
ExecutionTimer<std::chrono::seconds> timer;
// code block here...
timer.stop();
}
return 0;
}
Since the class is a template we can specify real easily in how we want our time to be measured & displayed. This is a very handy utility class template for doing bench marking and is very easy to use.
If you want to safe time and lines of code you can make measuring the function execution time a one line macro:
a) Implement a time measuring class as already suggested above ( here is my implementation for android):
class MeasureExecutionTime{
private:
const std::chrono::steady_clock::time_point begin;
const std::string caller;
public:
MeasureExecutionTime(const std::string& caller):caller(caller),begin(std::chrono::steady_clock::now()){}
~MeasureExecutionTime(){
const auto duration=std::chrono::steady_clock::now()-begin;
LOGD("ExecutionTime")<<"For "<<caller<<" is "<<std::chrono::duration_cast<std::chrono::milliseconds>(duration).count()<<"ms";
}
};
b) Add a convenient macro that uses the current function name as TAG (using a macro here is important, else __FUNCTION__ will evaluate to MeasureExecutionTime instead of the function you wanto to measure
#ifndef MEASURE_FUNCTION_EXECUTION_TIME
#define MEASURE_FUNCTION_EXECUTION_TIME const MeasureExecutionTime measureExecutionTime(__FUNCTION__);
#endif
c) Write your macro at the begin of the function you want to measure. Example:
void DecodeMJPEGtoANativeWindowBuffer(uvc_frame_t* frame_mjpeg,const ANativeWindow_Buffer& nativeWindowBuffer){
MEASURE_FUNCTION_EXECUTION_TIME
// Do some time-critical stuff
}
Which will result int the following output:
ExecutionTime: For DecodeMJPEGtoANativeWindowBuffer is 54ms
Note that this (as all other suggested solutions) will measure the time between when your function was called and when it returned, not neccesarily the time your CPU was executing the function. However, if you don't give the scheduler any change to suspend your running code by calling sleep() or similar there is no difference between.
It is a very easy to use method in C++11.
We can use std::chrono::high_resolution_clock from header
We can write a method to print the method execution time in a much readable form.
For example, to find the all the prime numbers between 1 and 100 million, it takes approximately 1 minute and 40 seconds.
So the execution time get printed as:
Execution Time: 1 Minutes, 40 Seconds, 715 MicroSeconds, 715000 NanoSeconds
The code is here:
#include <iostream>
#include <chrono>
using namespace std;
using namespace std::chrono;
typedef high_resolution_clock Clock;
typedef Clock::time_point ClockTime;
void findPrime(long n, string file);
void printExecutionTime(ClockTime start_time, ClockTime end_time);
int main()
{
long n = long(1E+8); // N = 100 million
ClockTime start_time = Clock::now();
// Write all the prime numbers from 1 to N to the file "prime.txt"
findPrime(n, "C:\\prime.txt");
ClockTime end_time = Clock::now();
printExecutionTime(start_time, end_time);
}
void printExecutionTime(ClockTime start_time, ClockTime end_time)
{
auto execution_time_ns = duration_cast<nanoseconds>(end_time - start_time).count();
auto execution_time_ms = duration_cast<microseconds>(end_time - start_time).count();
auto execution_time_sec = duration_cast<seconds>(end_time - start_time).count();
auto execution_time_min = duration_cast<minutes>(end_time - start_time).count();
auto execution_time_hour = duration_cast<hours>(end_time - start_time).count();
cout << "\nExecution Time: ";
if(execution_time_hour > 0)
cout << "" << execution_time_hour << " Hours, ";
if(execution_time_min > 0)
cout << "" << execution_time_min % 60 << " Minutes, ";
if(execution_time_sec > 0)
cout << "" << execution_time_sec % 60 << " Seconds, ";
if(execution_time_ms > 0)
cout << "" << execution_time_ms % long(1E+3) << " MicroSeconds, ";
if(execution_time_ns > 0)
cout << "" << execution_time_ns % long(1E+6) << " NanoSeconds, ";
}
I recommend using steady_clock which is guarunteed to be monotonic, unlike high_resolution_clock.
#include <iostream>
#include <chrono>
using namespace std;
unsigned int stopwatch()
{
static auto start_time = chrono::steady_clock::now();
auto end_time = chrono::steady_clock::now();
auto delta = chrono::duration_cast<chrono::microseconds>(end_time - start_time);
start_time = end_time;
return delta.count();
}
int main() {
stopwatch(); //Start stopwatch
std::cout << "Hello World!\n";
cout << stopwatch() << endl; //Time to execute last line
for (int i=0; i<1000000; i++)
string s = "ASDFAD";
cout << stopwatch() << endl; //Time to execute for loop
}
Output:
Hello World!
62
163514
Since none of the provided answers are very accurate or give reproducable results I decided to add a link to my code that has sub-nanosecond precision and scientific statistics.
Note that this will only work to measure code that takes a (very) short time to run (aka, a few clock cycles to a few thousand): if they run so long that they are likely to be interrupted by some -heh- interrupt, then it is clearly not possible to give a reproducable and accurate result; the consequence of which is that the measurement never finishes: namely, it continues to measure until it is statistically 99.9% sure it has the right answer which never happens on a machine that has other processes running when the code takes too long.
https://github.com/CarloWood/cwds/blob/master/benchmark.h#L40
You can have a simple class which can be used for this kind of measurements.
class duration_printer {
public:
duration_printer() : __start(std::chrono::high_resolution_clock::now()) {}
~duration_printer() {
using namespace std::chrono;
high_resolution_clock::time_point end = high_resolution_clock::now();
duration<double> dur = duration_cast<duration<double>>(end - __start);
std::cout << dur.count() << " seconds" << std::endl;
}
private:
std::chrono::high_resolution_clock::time_point __start;
};
The only thing is needed to do is to create an object in your function at the beginning of that function
void veryLongExecutingFunction() {
duration_calculator dc;
for(int i = 0; i < 100000; ++i) std::cout << "Hello world" << std::endl;
}
int main() {
veryLongExecutingFunction();
return 0;
}
and that's it. The class can be modified to fit your requirements.
C++11 cleaned up version of Jahid's response:
#include <chrono>
#include <thread>
void long_operation(int ms)
{
/* Simulating a long, heavy operation. */
std::this_thread::sleep_for(std::chrono::milliseconds(ms));
}
template<typename F, typename... Args>
double funcTime(F func, Args&&... args){
std::chrono::high_resolution_clock::time_point t1 =
std::chrono::high_resolution_clock::now();
func(std::forward<Args>(args)...);
return std::chrono::duration_cast<std::chrono::milliseconds>(
std::chrono::high_resolution_clock::now()-t1).count();
}
int main()
{
std::cout<<"expect 150: "<<funcTime(long_operation,150)<<"\n";
return 0;
}
This is a very basic timer class which you can expand on depending on your needs. I wanted something straightforward which can be used cleanly in code. You can mess with it at coding ground with this link: http://tpcg.io/nd47hFqr.
class local_timer {
private:
std::chrono::_V2::system_clock::time_point start_time;
std::chrono::_V2::system_clock::time_point stop_time;
std::chrono::_V2::system_clock::time_point stop_time_temp;
std::chrono::microseconds most_recent_duration_usec_chrono;
double most_recent_duration_sec;
public:
local_timer() {
};
~local_timer() {
};
void start() {
this->start_time = std::chrono::high_resolution_clock::now();
};
void stop() {
this->stop_time = std::chrono::high_resolution_clock::now();
};
double get_time_now() {
this->stop_time_temp = std::chrono::high_resolution_clock::now();
this->most_recent_duration_usec_chrono = std::chrono::duration_cast<std::chrono::microseconds>(stop_time_temp-start_time);
this->most_recent_duration_sec = (long double)most_recent_duration_usec_chrono.count()/1000000;
return this->most_recent_duration_sec;
};
double get_duration() {
this->most_recent_duration_usec_chrono = std::chrono::duration_cast<std::chrono::microseconds>(stop_time-start_time);
this->most_recent_duration_sec = (long double)most_recent_duration_usec_chrono.count()/1000000;
return this->most_recent_duration_sec;
};
};
The use for this being
#include <iostream>
#include "timer.hpp" //if kept in an hpp file in the same folder, can also before your main function
int main() {
//create two timers
local_timer timer1 = local_timer();
local_timer timer2 = local_timer();
//set start time for timer1
timer1.start();
//wait 1 second
while(timer1.get_time_now() < 1.0) {
}
//save time
timer1.stop();
//print time
std::cout << timer1.get_duration() << " seconds, timer 1\n" << std::endl;
timer2.start();
for(long int i = 0; i < 100000000; i++) {
//do something
if(i%1000000 == 0) {
//return time since loop started
std::cout << timer2.get_time_now() << " seconds, timer 2\n"<< std::endl;
}
}
return 0;
}
This is for my university coursework.
I have a class called timestep that is going to be used as a typical timer in a game engine to calculate frame times, etc, and an application class.
I'm struggling to get my head around shared pointers, but am required to use one to access the timestep class from the application class. It doesn't throw up errors until the program is running, at which point it prints my "PRE TIMER" log to the console, and throws an exception after reaching timer->setStart(), flags the line start = ..... in the setStart method, and says **this** was nullptr.
Timestep.h:
#pragma once
#include <chrono>
namespace Engine {
class Timestep {
private:
std::chrono::high_resolution_clock::time_point start;
std::chrono::high_resolution_clock::time_point end;
public:
Timestep();
void setStart();
void setEnd();
float getTimeSeconds() const;
float GetTimeMilliSeconds() const;
};
}
timestep.cpp:
#pragma once
#include "engine_pch.h"
#include "core/timestep.h"
namespace Engine {
Timestep::Timestep(){}
void Timestep::setStart() {
start = std::chrono::high_resolution_clock::now();
}
void Timestep::setEnd() {
end = std::chrono::high_resolution_clock::now();
}
float Timestep::getTimeSeconds() const {
std::chrono::duration<float> time = end - start;
return time.count();
}
float Timestep::GetTimeMilliSeconds() const {
std::chrono::duration<float, std::milli> time = end - start;
return time.count();
}
}
application.cpp:
#include "engine_pch.h"
#include "core/application.h"
namespace Engine {
Application* Application::s_instance = nullptr;
std::shared_ptr<Timestep> timer;
Application::Application()
{
if (s_instance == nullptr)
{
s_instance = this;
}
log::log();
LOG_INFO("Logger init success");
}
Application::~Application()
{
}
void Application::run()
{
LOG_INFO("PRE TIMER");
timer->setStart();
LOG_INFO("POST TIMER");
while (s_instance) {
timer->setEnd();
float a = timer->getTimeSeconds();
LOG_INFO("Time since last frame is {0}", a);
timer->setStart();
}
}
}
Apparently, your timer in application.cpp is not pointing to any instance of Timestep, incurring the nullptr error. Explained simply, your shared pointer was not initialized.
Assuming that you want a separate instance of Timestep for each instance of Application, maybe you could solve the issue by initializing your std::shared_ptr<Timestep> timer;
Instead of
std::shared_ptr<Timestep> timer;
Try
std::shared_ptr<Timestep> timer(new Timestep());
I am interested in timing the execution time of a free function or a member function (template or not). Call TheFunc the function in question, its call being
TheFunc(/*parameters*/);
or
ReturnType ret = TheFunc(/*parameters*/);
Of course I could wrap these function calls as follows :
double duration = 0.0 ;
std::clock_t start = std::clock();
TheFunc(/*parameters*/);
duration = static_cast<double>(std::clock() - start) / static_cast<double>(CLOCKS_PER_SEC);
or
double duration = 0.0 ;
std::clock_t start = std::clock();
ReturnType ret = TheFunc(/*parameters*/);
duration = static_cast<double>(std::clock() - start) / static_cast<double>(CLOCKS_PER_SEC);
but I would like to do something more elegant than this, namely (and from now on I will stick to the void return type) as follows :
Timer thetimer ;
double duration = 0.0;
thetimer(*TheFunc)(/*parameters*/, duration);
where Timer is some timing class that I would like to design and that would allow me to write the previous code, in such way that after the exectution of the last line of previous code the double duration will contain the execution time of
TheFunc(/*parameters*/);
but I don't see how to do this, nor if the syntax/solution I aim for is optimal...
With variadic template, you may do:
template <typename F, typename ... Ts>
double Time_function(F&& f, Ts&&...args)
{
std::clock_t start = std::clock();
std::forward<F>(f)(std::forward<Ts>(args)...);
return static_cast<double>(std::clock() - start) / static_cast<double>(CLOCKS_PER_SEC);
}
I really like boost::cpu_timer::auto_cpu_timer, and when I cannot use boost I simply hack my own:
#include <cmath>
#include <string>
#include <chrono>
#include <iostream>
class AutoProfiler {
public:
AutoProfiler(std::string name)
: m_name(std::move(name)),
m_beg(std::chrono::high_resolution_clock::now()) { }
~AutoProfiler() {
auto end = std::chrono::high_resolution_clock::now();
auto dur = std::chrono::duration_cast<std::chrono::microseconds>(end - m_beg);
std::cout << m_name << " : " << dur.count() << " musec\n";
}
private:
std::string m_name;
std::chrono::time_point<std::chrono::high_resolution_clock> m_beg;
};
void foo(std::size_t N) {
long double x {1.234e5};
for(std::size_t k = 0; k < N; k++) {
x += std::sqrt(x);
}
}
int main() {
{
AutoProfiler p("N = 10");
foo(10);
}
{
AutoProfiler p("N = 1,000,000");
foo(1000000);
}
}
This timer works thanks to RAII. When you build the object within an scope you store the timepoint at that point in time. When you leave the scope (that is, at the corresponding }) the timer first stores the timepoint, then calculates the number of ticks (which you can convert to a human-readable duration), and finally prints it to screen.
Of course, boost::timer::auto_cpu_timer is much more elaborate than my simple implementation, but I often find my implementation more than sufficient for my purposes.
Sample run in my computer:
$ g++ -o example example.com -std=c++14 -Wall -Wextra
$ ./example
N = 10 : 0 musec
N = 1,000,000 : 10103 musec
EDIT
I really liked the implementation suggested by #Jarod42. I modified it a little bit to offer some flexibility on the desired "units" of the output.
It defaults to returning the number of elapsed microseconds (an integer, normally std::size_t), but you can request the output to be in any duration of your choice.
I think it is a more flexible approach than the one I suggested earlier because now I can do other stuff like taking the measurements and storing them in a container (as I do in the example).
Thanks to #Jarod42 for the inspiration.
#include <cmath>
#include <string>
#include <chrono>
#include <algorithm>
#include <iostream>
template<typename Duration = std::chrono::microseconds,
typename F,
typename ... Args>
typename Duration::rep profile(F&& fun, Args&&... args) {
const auto beg = std::chrono::high_resolution_clock::now();
std::forward<F>(fun)(std::forward<Args>(args)...);
const auto end = std::chrono::high_resolution_clock::now();
return std::chrono::duration_cast<Duration>(end - beg).count();
}
void foo(std::size_t N) {
long double x {1.234e5};
for(std::size_t k = 0; k < N; k++) {
x += std::sqrt(x);
}
}
int main() {
std::size_t N { 1000000 };
// profile in default mode (microseconds)
std::cout << "foo(1E6) takes " << profile(foo, N) << " microseconds" << std::endl;
// profile in custom mode (e.g, milliseconds)
std::cout << "foo(1E6) takes " << profile<std::chrono::milliseconds>(foo, N) << " milliseconds" << std::endl;
// To create an average of `M` runs we can create a vector to hold
// `M` values of the type used by the clock representation, fill
// them with the samples, and take the average
std::size_t M {100};
std::vector<typename std::chrono::milliseconds::rep> samples(M);
for(auto & sample : samples) {
sample = profile(foo, N);
}
auto avg = std::accumulate(samples.begin(), samples.end(), 0) / static_cast<long double>(M);
std::cout << "average of " << M << " runs: " << avg << " microseconds" << std::endl;
}
Output (compiled with g++ example.cpp -std=c++14 -Wall -Wextra -O3):
foo(1E6) takes 10073 microseconds
foo(1E6) takes 10 milliseconds
average of 100 runs: 10068.6 microseconds
You can do it the MatLab way. It's very old-school but simple is often good:
tic();
a = f(c);
toc(); //print to stdout, or
auto elapsed = toc(); //store in variable
tic() and toc() can work to a global variable. If that's not sufficient, you can create local variables with some macro-magic:
tic(A);
a = f(c);
toc(A);
I'm a fan of using RAII wrappers for this type of stuff.
The following example is a little verbose but it's more flexible in that it works with arbitrary scopes instead of being limited to a single function call:
class timing_context {
public:
std::map<std::string, double> timings;
};
class timer {
public:
timer(timing_context& ctx, std::string name)
: ctx(ctx),
name(name),
start(std::clock()) {}
~timer() {
ctx.timings[name] = static_cast<double>(std::clock() - start) / static_cast<double>(CLOCKS_PER_SEC);
}
timing_context& ctx;
std::string name;
std::clock_t start;
};
timing_context ctx;
int main() {
timer_total(ctx, "total");
{
timer t(ctx, "foo");
// Do foo
}
{
timer t(ctx, "bar");
// Do bar
}
// Access ctx.timings
}
The downside is that you might end up with a lot of scopes that only serve to destroy the timing object.
This might or might not satisfy your requirements as your request was a little vague but it illustrates how using RAII semantics can make for some really nice reusable and clean code. It can probably be modified to look a lot better too!
I'm trying to create a step sequencer in C++ that will eventually send out MIDI data. I created it by having a clock on its own thread that calculates the amount of time since the last beat, and if it is time for the next beat, it writes a piece of data to the console.
However, I find that no matter what I set the BPM to, I get messages at a rate that is obviously too slow. I can't seem to figure out why the timing on this thread is wrong, and it doesn't help that I'm not terribly familiar with how the std::chrono library works. Thoughts?
Code below:
#include <thread>
#include <mutex>
#include <chrono>
#include <vector>
#include <iostream>
class StepSequencer {
public:
StepSequencer();
~StepSequencer();
void run();
void setBeatsPerMinute(float bpm);
void addNote(int noteValue, int beatIndex);
void playNote(int beatIndex);
protected:
int mNumberOfBeatBins;
int mSequencerPlayhead;
float mBeatsPerMinute;
float mSecondsPerBeat;
std::vector<int> mBeatBins;
std::mutex mMutex;
std::thread mSequencerThread;
bool mRunSequencerThread;
std::chrono::time_point<std::chrono::system_clock> mLastBeatTime;
std::chrono::time_point<std::chrono::system_clock> mCurrentTime;
};
#include "stdafx.h"
#include "StepSequencer.h"
StepSequencer::StepSequencer() {
mNumberOfBeatBins = 16;
for(int i = 0; i < 16; i++) {
mBeatBins.push_back(0);
}
mBeatsPerMinute = 0;
mSecondsPerBeat = 1;
mLastBeatTime = std::chrono::system_clock::now();
mCurrentTime = std::chrono::system_clock::now();
mSequencerPlayhead = 0;
mRunSequencerThread = false;
mSequencerThread = std::thread(&StepSequencer::run, this);
}
StepSequencer::~StepSequencer() {
if(mSequencerThread.joinable()) {
mSequencerThread.join();
}
}
void StepSequencer::run() {
mRunSequencerThread = true;
while(mRunSequencerThread) {
mCurrentTime = std::chrono::system_clock::now();
mMutex.lock();
if (std::chrono::duration_cast<std::chrono::seconds>(mCurrentTime - mLastBeatTime).count() > mSecondsPerBeat) {
mSequencerPlayhead++;
mSequencerPlayhead = mSequencerPlayhead % mNumberOfBeatBins;
playNote(mSequencerPlayhead);
mLastBeatTime = std::chrono::system_clock::now();
}
mMutex.unlock();
this_thread::sleep_for(std::chrono::milliseconds(1));
}
}
void StepSequencer::setBeatsPerMinute(float bpm) {
mMutex.lock();
mBeatsPerMinute = bpm;
if(mBeatsPerMinute > 0) {
mSecondsPerBeat = 60.0 / mBeatsPerMinute;
}
else {
mSecondsPerBeat = 1;
}
mMutex.unlock();
}
void StepSequencer::addNote(int noteValue, int beatIndex) {
mBeatBins[beatIndex] = noteValue;
}
void StepSequencer::playNote(int beatIndex) {
std::cout << mBeatBins[beatIndex] << std::endl;
}
std::chrono::seconds has a representation of 'A signed integral type of at least 35 bits'. So you are going to get a value of count() which increments only once per second, giving the option of 60,30,20,15,12, etc. beats per minute.
Work in milliseconds or use a custom duration which is backed by a floating point value instead.
I am trying to make a Clock with the timeGetTime function and some others. But I keep getting an exception error. I know mayby the quality of the program is not really good, but I was just trying to get it work. It's supposed to be a singleton. I hope you can help me!
// The Clock header file
// The Clock API for meassuring time.
#include<Windows.h>
#include<WinBase.h>
#include<MMSystem.h>
class cTime
{
private:
double m_Ns;
double m_Ms;
double m_S;
public:
// Set Values
void SetN(double N) {m_Ns = N;}
void SetM(double M) {m_Ns = M;}
void SetS(double S) {m_Ns = S;}
// Get Values
double GetN() {return m_Ns;}
double GetM() {return m_Ms;}
double GetS() {return m_S;}
// GetTime functions
//int GetDiffrenceNs();
//int GetDiffrenceMs();
//int GetDiffrenceS();
};
class cClock
{
private:
cTime m_CurrentTime; // CurrentTime object
static cClock* m_pClock; // Pointer to only instance
cTime m_LastTime; // LastTime object
bool m_PerformanceCounter; // Set to true if the performance counter is available
double m_Frequency; // Tells the frequenty of the PerformanceCounter. The value that the PerformanceCounter will increase each second.
double m_CounterTime; // The Counter of the PerformanceCounter.
double m_Trillingstijd; // How long one count of the performance counter will take.
public:
static cClock* GetClock();
cTime CurrentTime(); // Get the CurrentTime.
cTime LastTime(); // Get the LastTime.
// Virtual destructor.
virtual ~cClock();
protected:
// Protected constructor.
cClock();
};
// The clock cpp file
#include "Clock.h"
cClock* cClock::m_pClock = 0;
cClock* cClock::GetClock()
{
//BOOL perf_flag; // Timer Selection Flag
//double time_factor; // Time Scaling Factor
//LONGLONG last_time; // Previous timer value
//LONGLONG perf_cnt;
if (QueryPerformanceFrequency((LARGE_INTEGER *) &m_pClock->m_Frequency))
{
QueryPerformanceCounter((LARGE_INTEGER *) &m_pClock->m_CounterTime);
m_pClock->m_PerformanceCounter = true;
m_pClock->m_Trillingstijd=1.0/m_pClock->m_Frequency;
double LastedSeconds = m_pClock->m_CounterTime/m_pClock->m_Frequency;
m_pClock->m_LastTime.SetN(LastedSeconds*1000000);
m_pClock->m_LastTime.SetM(LastedSeconds*1000);
m_pClock->m_LastTime.SetS(LastedSeconds);
}
else
{
m_pClock->m_PerformanceCounter = false;
double LastedMiliseconds = timeGetTime();
m_pClock->m_LastTime.SetN(LastedMiliseconds*1000);
m_pClock->m_LastTime.SetM(LastedMiliseconds);
m_pClock->m_LastTime.SetS(LastedMiliseconds/1000);
}
return cClock::m_pClock;
}
cTime cClock::LastTime()
{
return m_LastTime;
}
cTime cClock::CurrentTime()
{
if(m_PerformanceCounter)
{
QueryPerformanceCounter((LARGE_INTEGER *) &m_CounterTime);
double LastedSeconds = m_CounterTime/m_Frequency;
m_CurrentTime.SetN(LastedSeconds*1000000);
m_CurrentTime.SetM(LastedSeconds*1000);
m_CurrentTime.SetS(LastedSeconds);
}
else
{
int LastedMiliseconds = timeGetTime();
m_CurrentTime.SetN(LastedMiliseconds*1000);
m_CurrentTime.SetM(LastedMiliseconds);
m_CurrentTime.SetS(LastedMiliseconds/1000);
}
m_LastTime = m_CurrentTime;
return m_CurrentTime;
}
This is my main, really simple but I just tried to get it to work but it doesn't...
#include "Clock.h"
#include<iostream>
using namespace std;
int main()
{
cClock* Clock = cClock::GetClock();
cTime Test = Clock->CurrentTime();
cout << Test.GetN();
cout << Test.GetM();
cout << Test.GetS();
int temp;
cin >> temp;
return 0;
}
It seems that the method cClock* cClock::GetClock() uses m_pClock without initializing it (it is still 0).
You are never creating an instance of cClock, just accessing a null pointer to one.
If you really think a singleton is a good idea, then cClock::GetClock() will have to create one if it doesn't already exist; along the lines of
cClock* cClock::GetClock()
{
if (!m_pClock) {
m_pClock = new cClock;
}
// remainder of function
return m_pClock;
}
Note that this isn't thread-safe, and also introduces a memory leak. Singletons are difficult to implement in C++, and best avoided unless there is a genuine reason for wanting one. I would move the logic of GetClock() into a public constructor, and allow client code to create and destroy clock objects as it sees fit.