wall clock time in milliseconds to time c code sections

[pedro.ballester]

Hi everyone,

I am struggling with the following problem. I would like to measure the
wall clock time required to run a section of the code with a precision
of milliseconds. The attached code does the job on Windows Xp. However,
the code is not portable, as it fails to compile on Linux Red Hat. This
is the command and the errors:

# gcc -c time_loop.c
time_loop.c: In function 'main':
time_loop.c:34: error: storage size of 'tstruct1' isn't known
time_loop.c:34: error: storage size of 'tstruct2' isn't known
time_loop.c:26: warning: return type of 'main' is not 'int'

I will be grateful if anyone could tell know how to fix this problem so
that I can use the same code both on WinXp and Linux. In case it is not
possible, it will be very helpful to have alternative, preferably
concise, code that works on Linux.

Thanks in advance,

Pedro

Ps: and this is time_loop.c

#include <math.h>
#include <stdio.h>
#include <stdlib.h>
#include <sys/types.h>
#include <sys/timeb.h>

/* GLOBAL PARAMETERS DECLARATION */

#define NM 25000000

/* MAIN ROUTINE */

void main(void)
{
int i;
long idb; /* with "register", it seems to take longer! */
/* register long idb; */
double tms1, tms2, telapsed;
float diff[12];
float vec_a[12]={6., 3., 4., 3., 7., 2., 1., 3., 8., 4., 9., 3.};
float vec_b[12]={3., 7., 2., 1., 3., 8., 4., 9., 6., 3., 4., 3.};
struct __timeb64 tstruct1, tstruct2;


/* Starting time */
_ftime64( &tstruct1 );
tms1=(double)tstruct1.time+((double)tstruct1.millitm/1000.0);


for(idb=0; idb < NM; idb++)
{
for(i=0; i < 12; i++) diff=vec_a-vec_a;
}


/* Finishing time */
_ftime64( &tstruct2 );
tms2=(double)tstruct2.time+((double)tstruct2.millitm/1000.0);
telapsed=tms2-tms1;


printf("It took:\t%lf seconds to calculate diff %d times\n",
telapsed, NM );

}

 

[Spiros Bousbouras]

Hi everyone,

I am struggling with the following problem. I would like to measure the
wall clock time required to run a section of the code with a precision
of milliseconds. The attached code does the job on Windows Xp. However,
the code is not portable, as it fails to compile on Linux Red Hat. This
is the command and the errors:

# gcc -c time_loop.c
time_loop.c: In function 'main':
time_loop.c:34: error: storage size of 'tstruct1' isn't known
time_loop.c:34: error: storage size of 'tstruct2' isn't known
time_loop.c:26: warning: return type of 'main' is not 'int'

I will be grateful if anyone could tell know how to fix this problem so
that I can use the same code both on WinXp and Linux. In case it is not
possible, it will be very helpful to have alternative, preferably
concise, code that works on Linux.

Standard C does not offer a way to measure milliseconds
therefore I don't think there is a way to have such code
which works both on Linux and Windows. For Linux specific
advice you should ask at comp.os.linux.development.apps

But there is a way to fix the following warning on both systems
time_loop.c:26: warning: return type of 'main' is not 'int'
I'll leave it as an exercise to find how.

 

[Spiros Bousbouras]

If this is the warning your compiler gave you it's
either broken or the people who wrote it have a
very strange sense of humor. But I suspect that
you simply didn't copy the warning correctly. Cut
and paste is the only reliable method for programmes
and compiler messages.

 

[Keith Thompson]

If this is the warning your compiler gave you it's
either broken or the people who wrote it have a
very strange sense of humor. But I suspect that
you simply didn't copy the warning correctly. Cut
and paste is the only reliable method for programmes
and compiler messages.

What do you mean? The OP's program had:

void main(void)
{
...
}

The warning seems perfectly correct; he defined a function called
"main" whose return type is not int.

And yes, that's the exact warning message I get from gcc for
"void main(void)".

The line number doesn't match the code he posted, but that indicates a
copy-and-paste error for the code, not for the warning.

 

[Spiros Bousbouras]

What do you mean?

My mind worked strangely. I understood
"return type of 'main' is not 'int'"
not as referring to main as appears in the
programme but as saying that the return
value of main should not be int.

The warning is indeed correct.

 

[Ben Bacarisse]

Hi everyone,

I am struggling with the following problem. I would like to measure the
wall clock time required to run a section of the code with a precision
of milliseconds.

I will be grateful if anyone could tell know how to fix this problem so
that I can use the same code both on WinXp and Linux. In case it is not
possible, it will be very helpful to have alternative, preferably
concise, code that works on Linux.

This can't be done in standard (and hence portable) C. In such cases
it is often best to go the Unix(ish) route and use a function
specified in the POSIX standard since there are POSIX C libraries for
a lot of systems (including MS ones).

<offtopic>The POSIX function you want is gettimeofday. More
information and code examples would probably follow if you post on
comp.unix.programmer.</offtopic>