How to Measure Elapsed Time in C++?

Accuracy is implementation defined on Widows/MSVC it measures in nanoseconds but minimal step could be 100ns or more. If you need high accuracy you’ll need to buy hardware that can supply it and use its libraries. On my x86-64 Linux Ubuntu 18.04 system with the gcc compiler, clock_getres() returns a resolution of 1 ns. “Realtime” does NOT mean that it is a good clock to use for “realtime” operating systems, or precise timing. Rather, it means it is a clock which will be adjusted to the “real time”, or actual “world time”, periodically, if the clock drifts. Again, do NOT use this clock for precise timing usages, as it can be adjusted forwards or backwards at any time by the system, outside of your control.

c++ measure time

Dozens of companies have come up with “metrics” to measure performance – and none of them truly encapsulate the “value” of a programmer to the company. The term “load time” describes the stage at which all the programs are loaded into memory with the aid of a loader and is typically followed by. The sleep() function enables users to wait for a running thread for a specified amount of time. While the sleep() function will put the current executable to sleep for the amount of time specified by the thread, other CPU operations will continue to run smoothly. There are many methods available in calculating the time taken by a function. Even if you could meassure time that accurately, the meassure would still be flawed, because your pc does a lot more than execute a single function.

How to measure time taken by a function in C?

If you don’t care about being tied to Windows, you can try the high resolution timer. It’s is a lot more precise than time(), which only has a precision of a single second because it the uses UNIX format. Because of the precision over time provided by chrono and removing the possiblities of error involving due difference in time and date and it is fast. Also, it’s important to know various types of times which have to be considered, while measuring the time if a program/function. Finally, instead of printing the difference you can store it in a signed long.

It includes the header which provides access to the current time using system_clock(). The system_clock is designed to represent the real-time and used by all processes running on the system. After which the difference between the end and the beg variable is obtained, and the result is cast into milliseconds precision in the statement duration_cast(end – beg). This gives us the time taken between the first time the clock function is called, and the last time is was called. In the end, the elapsed time is displayed using the count function.

In the main loop of your program call ticktimer_tick and it will decide whether the appropriate amount of time has passed to invoke the callback. For Unix or Linux based system, you can use gettimeofday(). Following is a sample C program where we measure time taken by fun(). The function fun() waits for enter key press to terminate. Clock estimates the CPU time used by your program; that’s the time the CPU has been busy executing instructions belonging to your program.

c++ measure time

Use QueryPerformanceFrequency() as described in Orwells answer or use the GetSystemTimeAsFileTime() function. The latter has 100 ns granularity but does not increment at that rate. Its increment depends on underlaying hardware and Logistics Software Management, ERP Logistics System the setting of multimedia timer resolution. Keep in mind that the frequency returned by QueryPerformanceFrequency() is treated as a constant. However, since it is generated by hardware it has an offset and a drift in time too.

With this article at OpenGenus IQ, you have the basic knowledge of measuring time in C++ and you can use it effectively in production code now. Syntax and semantic analysis are a couple common tasks carried out at compile time. The assignment of specific computer program instructions to certain physical memory locations is another feature of compile time.

time() function

Time is one of the most valuable resources known to humans. Time management is crucial because it enables you to accomplish more in less time hence increasing your efficiency. It’s a specific stage at which the commands in computer programs or code are carried out is referred to as execution time. Reading programs instructions to perform tasks or complete activities is one of the fundamental operations that take place at execution time. In simple words, measuring time of a function or a program is a measure of how long an algorithm takes to run in relation to the size of the input.

The process of converting computer programs and code into a form that the CPU can understand, or machine-readable code, is known as compile-time. Code in the source language is converted to a particular target language at build time. Therefore, it’s highly important to know measuring time of a function or a program which ultimately results in improving the efficiency of thast particular function or program. Inversely, CPU Time describes the period of time when the CPU was working to process the program’s instructions.

  • Thus, if you use this code, only rely on differences between times, not the absolute time itself.
  • Again, do NOT use this clock for precise timing usages, as it can be adjusted forwards or backwards at any time by the system, outside of your control.
  • To get the elapsed time, we can get the time using clock() at the beginning, and at the end of the tasks, then subtract the values to get the differences.
  • Measuring periods in time by using QueryPerformanceCounter() will typically be accompanied by errors of many microseconds per second.

Works in C on Linux or POSIX systems, and allows you to choose the clock to use! I choose the CLOCK_MONOTONIC_RAW clock, which is best for obtaining timestamps used to time things on your system. I demonstrate this in the get_estimated_resolution() function of my timinglib.c timing library intended for Linux. (or a PC for that matter, or you need to time your timer interrupts themselves?) Here’s a solution that uses the x86 CPU timestamp counter directly… Not because this is good practice, or should be done, ever, when running under an OS… To initialize and start a timer, call ticktimer_init.

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The CPU time does not account for the time spent waiting for other processes, such as I/O activities, to finish. No clock on a consumer grade computer is going to measure with picosecond accuracy. The call to get the current time alone is going to take at least tens of nanoseconds. Struct timeval contains two components, the second and the microsecond. A timestamp with microsecond precision is represented as seconds since the epoch stored in the tv_sec field and the fractional microseconds in tv_usec.

This can be considered the rough “practical resolution” of these functions. See that test code in timinglib_get_resolution.c, and see the definition for my get_estimated_resolution() and get_specified_resolution() functions in timinglib.c. Below program to demonstrate how to measure execution time using time() function. The standard C library provides the time function and it is useful if you only need to compare seconds. If you need millisecond precision, though, the most portable way is to call timespec_get. It can tell time up to nanosecond precision, if the system supports.

Software Engineering

For measuring elapsed time, two timestamps would be collected. One at the beginning of the code and the other at the end. Then we would subtract the two timestamps, and the time difference between the two would provide us with the elapsed time. The following code calculates elapsed time using a system-wide real-time clock, identified by CLOCK_REALTIME, whose time represents seconds and nanoseconds since the Epoch. You might be wondering how we measure time in C++ and most important is what kind of time we measure in C++?

I just need a microsecond timestamp to calculate scrolling inertia. Standard C++ does not have a time function with subsecond precision. Marks a previously allocated ticktimer struct as free.

Thus you cannot just ignore tv_sec and expect sensible results. Note that the time returned by the Windows branch is milliseconds since the system started, while the time returned by the Unix branch is milliseconds since 1970. Thus, if you use this code, only rely on differences between times, not the absolute time itself. A complete C++ program demonstrating the procedure is given below. We fill up a vector with some random numbers and measure the time taken by sort() function to sort this vector.