I am using clock function for my c program to print execution time of current program.I am getting wrong time in output.I want to display time in seconds,milliseconds and microseconds.
#include <stdio.h>
#include <unistd.h>
#include <time.h>
int main()
{
clock_t start = clock();
sleep(3);
clock_t end = clock();
double time_taken = (double)(end - start)/CLOCKS_PER_SEC; // in seconds
printf("time program took %f seconds to execute \n", time_taken);
return 0;
}
time ./time
time program took 0.081000 seconds to execute
real 0m3.002s
user 0m0.000s
sys 0m0.002s
I expect output around 3 seconds however it display wrong.
As you see if I run this program using Linux command time I am getting correct time,I want to display same time using my c program.
Contrary to popular belief, the clock() function retrieves CPU time, not elapsed clock time as the name confusingly may induce people to believe.
Here is the language from the C Standard:
7.27.2.1 The clock function
Synopsis
#include <time.h>
clock_t clock(void);
Description
The clock function determines the processor time used.
Returns
The clock function returns the implementation’s best approximation to the processor time used by the program since the beginning of an implementation-defined era related only to the program invocation. To determine the time in seconds, the value returned by the clock function should be divided by the value of the macro CLOCKS_PER_SEC. If the processor time used is not available, the function returns the value (clock_t)(−1). If the value cannot be represented, the function returns an unspecified value.
To retrieve the elapsed time, you should use one of the following:
the time() function with a resolution of 1 second
the timespec_get() function which may be more precise, but might not be available on all systems
the gettimeofday() system call available on linux systems
the clock_gettime() function.
See What specifically are wall-clock-time, user-cpu-time, and system-cpu-time in UNIX? for more information on this subject.
Here is a modified version using gettimeoday():
#include <stdio.h>
#include <unistd.h>
#include <sys/time.h>
int main() {
struct timeval start, end;
gettimeofday(&start, NULL);
sleep(3);
gettimeofday(&end, NULL);
double time_taken = end.tv_sec + end.tv_usec / 1e6 -
start.tv_sec - start.tv_usec / 1e6; // in seconds
printf("time program took %f seconds to execute\n", time_taken);
return 0;
}
Output:
time program took 3.005133 seconds to execute
I have read several forums with the same title, although what I am after is NOT a way to find out how long it takes my computer to execute the program.
I am interested in finding out how long the program is in use by the user. I have looked at several functions inside #include <time.h>, however, it seems as though these functions (like clock_t) give the time it takes for my computer to execute my code which is not what I am after.
Thank you for your time.
EDIT:
I have done:
clock_t start, stop;
long int x;
double duration;
start = clock();
//code
stop = clock(); // get number of ticks after loop
// calculate time taken for loop
duration = ( double ) ( stop - start ) / CLOCKS_PER_SEC;
printf( "\nThe number of seconds for loop to run was %.2lf\n", duration );
I receive 0.16 from the program, however, when i timed it I got 1 minute and 14 seconds. how does this possibly add up?
The clock function counts CPU time used, not elapsed time. For a program that's 100% CPU-intensive, the time reported by clock will be close to wall time, but otherwise it's likely to be less -- often much less.
One easy way of measuring elapsed or "wall clock" time is with the time function:
time_t start, stop;
start = time(NULL);
// code
stop = time(NULL);
printf("The number of seconds for loop to run was %ld\n", stop - start);
This is a POSIX function, though -- it's not part of the core C standards, and it may not exist on, say, embedded versions of C.
I think you're looking for getrusage() function. It doesn't give you time consumed like how you use a stop-watch to time a function.
The function gives overall resource usage of the current program and splits it per-user. This is what the time command gives.
I'm trying to measure execution time in C using clock() under linux using the following:
#include <time.h>
#include <stdio.h>
#include <unistd.h>
int main(int argc, char const* argv[])
{
clock_t begin, end;
begin = clock();
sleep(2);
end = clock();
double spent = ((double)(end-begin)) / CLOCKS_PER_SEC;
printf("%ld %ld, spent: %f\n", begin, end, spent);
return 0;
}
The output is:
1254 1296, spent: 0.000042
The documentation says to divide the clock time by CLOCKS_PER_SEC to get the execution time in sec, but this seems pretty incorrect for a 2sec sleep.
What's the problem?
Sleeping takes almost no execution time. The program just has to schedule its wakeup and then put itself to sleep. While it's asleep, it is not executing. When it's woken up, it doesn't have to do anything at all. That all takes a very tiny fraction of a second.
It doesn't take more execution time to sleep longer. So the fact that there's a 2 second period when the program is not executing has no effect.
clock measures CPU time (in Linux at least). A sleeping process consumes no CPU time.
If you want to measure a time interval as if with a stopwatch, regardless of what your process is doing, use clock_gettime with CLOCK_MONOTONIC.
man clock() has the answer:
The clock() function returns an approximation of processor time used by the program.
Which clearly tells that clock() returns the processor time used by the program, not what you were expecting the total run time of the program which is typically done using gettimeofday.
I am learning C at the moment but I cannot see any existing examples of how I could run a command every X minutes.
I can see examples concerning how to time a command but that isn't what I want.
How can I run a command every X minutes in C?
You cannot do that in standard C99 (that is, using only the functions defined by the language standard).
You can do that on POSIX systems.
Assuming you focus a Linux system, read time(7) carefully. Then read about sleep(3), nanosleep(2), clock_gettime(2), getrusage(2) and some other syscalls(2)... etc...
The issue is to define what should happen if a command is running for more than X minutes.
Read some book about Advanced Linux Programming or Posix programming.
BTW, Linux has crontab(5) and all the related utilities are free software, so you could study their source code.
You could ask your calling thread to sleep for specified seconds.
#include <unistd.h>
unsigned int sleep(unsigned int seconds);
This conform to POSIX.1-2001.
sleep is a non-standard function. As mentioned here:
On UNIX, you shall include <unistd.h>.
On MS-Windows, Sleep is rather from <windows.h>
To do this, and allow other things to happen between calls, suggests using a thread.
This is untested pseudo code, but if you are using Linux, it could look something like this: (launch a thread and make it sleep for 60 seconds in the worker function loop between calls to your periodic function call)
void *OneMinuteCall(void *param);
pthread_t thread0;
int gRunning == 1;
OneMinuteCall( void * param )
{
int delay = (int)param;
while(gRunning)
{
some_func();//periodic function
sleep(delay);//sleep for 1 minute
}
}
void some_func(void)
{
//some stuff
}
int main(void)
{
int delay = 60; //(s)
pthread_create(&thread0, NULL, OneMinuteCall, delay);
//do some other stuff
//at some point you must set gRunning == 0 to exit loop;
//then terminate the thread
return 0;
}
As user3386109 suggested, using some form of clock for the delay and sleep to reduce cpu overhead would work. Example code to provide the basic concept. Note that the delay is based on an original reading of the time, (lasttime is updated based on desired delay, not the last reading of the clock). numsec should be set to 60*X to trigger every X minutes.
/* numsec = number of seconds per instance */
#define numsec 3
time_t lasttime, thistime;
int i;
lasttime = time(NULL);
for(i = 0; i < 5; i++){ /* any loop here */
while(1){
thistime = time(NULL);
if(thistime - lasttime >= numsec)
break;
if(thistime - lasttime >= 2)
sleep(thistime - lasttime - 1);
}
/* run periodic code here */
/* ... */
lasttime += numsec; /* update lasttime */
}
I don't know exactly how to word a search for this.. so I haven't had any luck finding anything.. :S
I need to implement a time delay in C.
for example I want to do some stuff, then wait say 1 minute, then continue on doing stuff.
Did that make sense? Can anyone help me out?
In standard C (C99), you can use time() to do this, something like:
#include <time.h>
:
void waitFor (unsigned int secs) {
unsigned int retTime = time(0) + secs; // Get finishing time.
while (time(0) < retTime); // Loop until it arrives.
}
By the way, this assumes time() returns a 1-second resolution value. I don't think that's mandated by the standard so you may have to adjust for it.
In order to clarify, this is the only way I'm aware of to do this with ISO C99 (and the question is tagged with nothing more than "C" which usually means portable solutions are desirable although, of course, vendor-specific solutions may still be given).
By all means, if you're on a platform that provides a more efficient way, use it. As several comments have indicated, there may be specific problems with a tight loop like this, with regard to CPU usage and battery life.
Any decent time-slicing OS would be able to drop the dynamic priority of a task that continuously uses its full time slice but the battery power may be more problematic.
However C specifies nothing about the OS details in a hosted environment, and this answer is for ISO C and ISO C alone (so no use of sleep, select, Win32 API calls or anything like that).
And keep in mind that POSIX sleep can be interrupted by signals. If you are going to go down that path, you need to do something like:
int finishing = 0; // set finishing in signal handler
// if you want to really stop.
void sleepWrapper (unsigned int secs) {
unsigned int left = secs;
while ((left > 0) && (!finishing)) // Don't continue if signal has
left = sleep (left); // indicated exit needed.
}
Here is how you can do it on most desktop systems:
#ifdef _WIN32
#include <windows.h>
#else
#include <unistd.h>
#endif
void wait( int seconds )
{ // Pretty crossplatform, both ALL POSIX compliant systems AND Windows
#ifdef _WIN32
Sleep( 1000 * seconds );
#else
sleep( seconds );
#endif
}
int
main( int argc, char **argv)
{
int running = 3;
while( running )
{ // do something
--running;
wait( 3 );
}
return 0; // OK
}
Here is how you can do it on a microcomputer / processor w/o timer:
int wait_loop0 = 10000;
int wait_loop1 = 6000;
// for microprocessor without timer, if it has a timer refer to vendor documentation and use it instead.
void
wait( int seconds )
{ // this function needs to be finetuned for the specific microprocessor
int i, j, k;
for(i = 0; i < seconds; i++)
{
for(j = 0; j < wait_loop0; j++)
{
for(k = 0; k < wait_loop1; k++)
{ // waste function, volatile makes sure it is not being optimized out by compiler
int volatile t = 120 * j * i + k;
t = t + 5;
}
}
}
}
int
main( int argc, char **argv)
{
int running = 3;
while( running )
{ // do something
--running;
wait( 3 );
}
return 0; // OK
}
The waitloop variables must be fine tuned, those did work pretty close for my computer, but the frequency scale thing makes it very imprecise for a modern desktop system; So don't use there unless you're bare to the metal and not doing such stuff.
Check sleep(3) man page or MSDN for Sleep
Although many implementations have the time function return the current time in seconds, there is no guarantee that every implementation will do so (e.g. some may return milliseconds rather than seconds). As such, a more portable solution is to use the difftime function.
difftime is guaranteed by the C standard to return the difference in time in seconds between two time_t values. As such we can write a portable time delay function which will run on all compliant implementations of the C standard.
#include <time.h>
void delay(double dly){
/* save start time */
const time_t start = time(NULL);
time_t current;
do{
/* get current time */
time(¤t);
/* break loop when the requested number of seconds have elapsed */
}while(difftime(current, start) < dly);
}
One caveat with the time and difftime functions is that the C standard never specifies a granularity. Most implementations have a granularity of one second. While this is all right for delays lasting several seconds, our delay function may wait too long for delays lasting under one second.
There is a portable standard C alternative: the clock function.
The clock function returns the implementation’s best approximation to the processor time used by the program since the beginning of an implementation-defined era related only to the program invocation. To determine the time in seconds, the value returned by the clock function should be divided by the value of the macro CLOCKS_PER_SEC.
The clock function solution is quite similar to our time function solution:
#include <time.h>
void delay(double dly){
/* save start clock tick */
const clock_t start = clock();
clock_t current;
do{
/* get current clock tick */
current = clock();
/* break loop when the requested number of seconds have elapsed */
}while((double)(current-start)/CLOCKS_PER_SEC < dly);
}
There is a caveat in this case similar to that of time and difftime: the granularity of the clock function is left to the implementation. For example, machines with 32-bit values for clock_t with a resolution in microseconds may end up wrapping the value returned by clock after 2147 seconds (about 36 minutes).
As such, consider using the time and difftime implementation of the delay function for delays lasting at least one second, and the clock implementation for delays lasting under one second.
A final word of caution: clock returns processor time rather than calendar time; clock may not correspond with the actual elapsed time (e.g. if the process sleeps).
For delays as large as one minute, sleep() is a nice choice.
If someday, you want to pause on delays smaller than one second, you may want to consider poll() with a timeout.
Both are POSIX.
There are no sleep() functions in the pre-C11 C Standard Library, but POSIX does provide a few options.
The POSIX function sleep() (unistd.h) takes an unsigned int argument for the number of seconds desired to sleep. Although this is not a Standard Library function, it is widely available, and glibc appears to support it even when compiling with stricter settings like --std=c11.
The POSIX function nanosleep() (time.h) takes two pointers to timespec structures as arguments, and provides finer control over the sleep duration. The first argument specifies the delay duration. If the second argument is not a null pointer, it holds the time remaining if the call is interrupted by a signal handler.
Programs that use the nanosleep() function may need to include a feature test macro in order to compile. The following code sample will not compile on my linux system without a feature test macro when I use a typical compiler invocation of gcc -std=c11 -Wall -Wextra -Wpedantic.
POSIX once had a usleep() function (unistd.h) that took a useconds_t argument to specify sleep duration in microseconds. This function also required a feature test macro when used with strict compiler settings. Alas, usleep() was made obsolete with POSIX.1-2001 and should no longer be used. It is recommended that nanosleep() be used now instead of usleep().
#define _POSIX_C_SOURCE 199309L // feature test macro for nanosleep()
#include <stdio.h>
#include <unistd.h> // for sleep()
#include <time.h> // for nanosleep()
int main(void)
{
// use unsigned sleep(unsigned seconds)
puts("Wait 5 sec...");
sleep(5);
// use int nanosleep(const struct timespec *req, struct timespec *rem);
puts("Wait 2.5 sec...");
struct timespec ts = { .tv_sec = 2, // seconds to wait
.tv_nsec = 5e8 }; // additional nanoseconds
nanosleep(&ts, NULL);
puts("Bye");
return 0;
}
Addendum:
C11 does have the header threads.h providing thrd_sleep(), which works identically to nanosleep(). GCC did not support threads.h until 2018, with the release of glibc 2.28. It has been difficult in general to find implementations with support for threads.h (Clang did not support it for a long time, but I'm not sure about the current state of affairs there). You will have to use this option with care.
Try sleep(int number_of_seconds)
sleep(int) works as a good delay. For a minute:
//Doing some stuff...
sleep(60); //Freeze for A minute
//Continue doing stuff...
Is it timer?
For WIN32 try http://msdn.microsoft.com/en-us/library/ms687012%28VS.85%29.aspx
you can simply call delay() function. So if you want to delay the process in 3 seconds, call delay(3000)...
If you are certain you want to wait and never get interrupted then use sleep in POSIX or Sleep in Windows. In POSIX sleep takes time in seconds so if you want the time to be shorter there are varieties like usleep() which uses microseconds. Sleep in Windows takes milliseconds, it is rare you need finer granularity than that.
It may be that you wish to wait a period of time but want to allow interrupts, maybe in the case of an emergency. sleep can be interrupted by signals but there is a better way of doing it in this case.
Therefore I actually found in practice what you do is wait for an event or a condition variable with a timeout.
In Windows your call is WaitForSingleObject. In POSIX it is pthread_cond_timedwait.
In Windows you can also use WaitForSingleObjectEx and then you can actually "interrupt" your thread with any queued task by calling QueueUserAPC. WaitForSingleObject(Ex) will return a code determining why it exited, so you will know when it returns a "TIMEDOUT" status that it did indeed timeout. You set the Event it is waiting for when you want it to terminate.
With pthread_cond_timedwait you can signal broadcast the condition variable. (If several threads are waiting on the same one, you will need to broadcast to wake them all up). Each time it loops it should check the condition. Your thread can get the current time and see if it has passed or it can look to see if some condition has been met to determine what to do. If you have some kind of queue you can check it. (Your thread will automatically have a mutex locked that it used to wait on the condition variable, so when it checks the condition it has sole access to it).
// Provides ANSI C method of delaying x milliseconds
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
void delayMillis(unsigned long ms) {
clock_t start_ticks = clock();
unsigned long millis_ticks = CLOCKS_PER_SEC/1000;
while (clock()-start_ticks < ms*millis_ticks) {
}
}
/*
* Example output:
*
* CLOCKS_PER_SEC:[1000000]
*
* Test Delay of 800 ms....
*
* start[2054], end[802058],
* elapsedSec:[0.802058]
*/
int testDelayMillis() {
printf("CLOCKS_PER_SEC:[%lu]\n\n", CLOCKS_PER_SEC);
clock_t start_t, end_t;
start_t = clock();
printf("Test Delay of 800 ms....\n", CLOCKS_PER_SEC);
delayMillis(800);
end_t = clock();
double elapsedSec = end_t/(double)CLOCKS_PER_SEC;
printf("\nstart[%lu], end[%lu], \nelapsedSec:[%f]\n", start_t, end_t, elapsedSec);
}
int main() {
testDelayMillis();
}
C11 has a function specifically for this:
#include <threads.h>
#include <time.h>
#include <stdio.h>
void sleep(time_t seconds) {
struct timespec time;
time.tv_sec = seconds;
time.tv_nsec = 0;
while (thrd_sleep(&time, &time)) {}
}
int main() {
puts("Sleeping for 5 seconds...");
sleep(5);
puts("Done!");
return 0;
}
Note that this is only available starting in glibc 2.28.
for C use in gcc.
#include <windows.h>
then use Sleep(); /// Sleep() with capital S. not sleep() with s .
//Sleep(1000) is 1 sec /// maybe.
clang supports sleep(), sleep(1) is for 1 sec time delay/wait.
For short delays (say, some microseconds) on Linux OS, you can use "usleep":
// C Program to perform short delays
#include <unistd.h>
#include <stdio.h>
int main(){
printf("Hello!\n");
usleep(1000000); // For a 1-second delay
printf("Bye!\n);
return 0;
system("timeout /t 60"); // waits 60s. this is only for windows vista,7,8
system("ping -n 60 127.0.0.1 >nul"); // waits 60s. for all windows
Write this code :
void delay(int x)
{ int i=0,j=0;
for(i=0;i<x;i++){for(j=0;j<200000;j++){}}
}
int main()
{
int i,num;
while(1) {
delay(500);
printf("Host name");
printf("\n");}
}