clock

The C++ Programming Language 4th edition, page 225 reads: A compiler may reorder code to improve performance as long as the result is identical to that of the simple order of execution . Some compilers, e.g. Visual C++ in release mode, will reorder this code: #include <time.h> ... auto t0 = clock(); auto r = veryLongComputation(); auto t1 = clock(); std::cout << r << " time: " << t1-t0 << endl; into this form: auto t0 = clock(); auto t1 = clock(); auto r = veryLongComputation(); std::cout << r << " time: " << t1-t0 << endl; which guarantees different result than original code (zero vs. greater

At the top and end of my program I use clock() to figure out how long my program takes to finish. Unfortunately, it appears to take half as long as it's reporting. I double checked this with the "time" command. My program reports: Completed in 45.86s Time command reports: real 0m22.837s user 0m45.735s sys 0m0.152s Using my cellphone to time it, it completed in 23s (aka: the "real" time). "User" time is the sum of all threads, which would make sense since I'm using OpenMP. (You can read about it here: What do 'real', 'user' and 'sys' mean in the output of time(1)? ) So, why is clock() reporting

There is a really interesting note here: http://en.cppreference.com/w/cpp/chrono/c/clock "Only the difference between two values returned by different calls to std::clock is meaningful, as the beginning of the std::clock era does not have to coincide with the start of the program. std::clock time may advance faster or slower than the wall clock, depending on the execution resources given to the program by the operating system. For example, if the CPU is shared by other processes, std::clock time may advance slower than wall clock. On the other hand, if the current process is multithreaded and

I'm trying to measure execution time of some commands in c++ by using the physical clock, but I have run into a problem that the process of reading off the measurement from the physical clock on the computer can take a long time. Here is the code: #include <string> #include <cstdlib> #include <iostream> #include <math.h> #include <time.h> int main() { int64_t mtime, mtime2, m_TSsum, m_TSssum, m_TSnum, m_TSmax; struct timespec t0; struct timespec t1; int i,j; for(j=0;j<10;j++){ m_TSnum=0;m_TSsum=0; m_TSssum=0; m_TSmax=0; for( i=0; i<10000000; i++) { clock_gettime(CLOCK_REALTIME,&t0); clock

We want to run a task every 1000 seconds (say). So we have timer.scheduleAtFixedRate(task, delay, interval); Mostly, this works fine. However, this is an embedded system and the user can change the real time clock. If they set it to a time in the past after we set up the timer, it seems the timer doesn't execute until the original real-time date/time. So if they set it back 3 days, the timer doesn't execute for 3 days :( Is this permissible behaviour, or a defect in the Java library? The Oracle javadocs don't seem to mention anything about the dependency or not on the underlying value of the

How can i generate an event at a specific time? For example, say I want to generate an alert at 8:00 AM that informs me its 8:00 AM (or an event that informs me of the current time at any given time). dtb Use the System.Threading.Timer class: var dt = ... // next 8:00 AM from now var timer = new Timer(callback, null, dt - DateTime.Now, TimeSpan.FromHours(24)); The callback delegate will be called the next time it's 8:00 AM and every 24 hours thereafter. See this SO question how to calculate the next 8:00 AM occurrence. Thunder Elaborating on dtb's answer this is how I implemented it. private

Hi I wanted to use the clock_gettime() function for measuring the performance of my code. I am unable to understand the difference between the different kinds of clocks used in the function from the man page descriptions. esp CLOCK_REALTIME, CLOCK_PROCESS_CPUTIME_ID CLOCK_THREAD_CPUTIME_ID Can someone explaing what each of these clocks do? R.. CLOCK_REALTIME reports the actual wall clock time. CLOCK_MONOTONIC is for measuring relative real time. It advances at the same rate as the actual flow of time but it's not subject to discontinuities from manual or automatic (NTP) adjustments to the

THis is not really a question, Sorry. I just wanted help on getting the package and class names of alarm and clocks of different android makers' clock and alarm. I have a listing here of HTC, Samsung, and stock android class names. But you can guess the package names. // HTC "com.htc.android.worldclock.TimerAlert",// "com.htc.android.worldclock.AlarmAlert",// // Samsung "com.sec.android.app.clockpackage.ClockPackage",// "com.sec.android.app.clockpackage.alarm.AlarmAlert",// // Motorola "com.motorola.blur.alarmclock.AlarmAlert",// "com.motorola.blur.alarmclock.AlarmClock",// "com.motorola.blur