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.
Measure wall clock time in c.
Using clock gettime function in c c.
For example if the cpu is shared by other processes std clock time may advance slower than wall clock.
The gettimeofday function returns the wall clock time elapsed since the epoch and store it in the timevalstructure expressed as seconds and microseconds.
Tp parameter points to a structure containing atleast the following members.
The function fun waits for enter key press to terminate.
The system s notion of the current greenwich time and the current time zone.
Do the work.
Note that this function does not strictly conform to iso c which specifies net cpu time as the return value.
In all multivalue basic languages you can use the time function to return the number of seconds from midnight.
Calculating the elapsed wall clock time of a program is helpful to determine how much time it actually takes for a program to complete.
Prototype syntax.
Wtime a c function which returns a reading of the wall clock time.
The clock function tells how much wall clock time has passed since the crt initialization during process start.
Fortunately all mpi implementations provide you with such a clock.
End clock.
Include sys time h int gettimeofday struct timeval restrict tp void restrict tzp.
The openmp system provides a function used as follows.
Following is a sample c program where we measure time taken by fun.
As it turns out c has many functions available to get the current time.
The clock gettime function gets the current time of the clock specified by clock id and puts it into the buffer pointed to by tp.
For that you will have to use chronometers.
It is defined in sys time h header file and takes two arguments the first arugment is reference to the timevalstructure and the second argument is a null pointer.
The obvious one is gettimeofday.
For parallel programming the important thing to measure is the elapsed wallclock time.
Cpu time used double end start clocks per sec.
There are a lot of ways to measure time in computer science but as a general rule of thumb you should always use a clock that measures the elapsed real time or wall time.
To obtain cpu times use the win32 getprocesstimes function.