Elapsed time of running a C program

I would like to know what lines of C code to add to a program so that it tells me the total time that the program takes to run. I guess there should be counter initialization near the beginning of main and one after the main function ends. Is the right header clock.h?

Thanks a lot...

Update I have a Win Xp machine. Is it just adding clock() at the beginning and another clock() at the end of the program? Then I can estimate the time difference. Yes, you're right it's time.h.

Here's my code:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <share.h>
#include <time.h>


void f(long double fb[], long double fA, long double fB);

int main() {

clock_t start, end;
start = clock();


const int ARRAY_SIZE = 11;

long double* z = (long double*) malloc(sizeof (long double) * ARRAY_SIZE);

int i;
long double A, B;

if (z == NULL) {
    printf("Out of memory\n");
    exit(-1);
}

A = 0.5;
B = 2;


for (i = 0; i < ARRAY_SIZE; i++) {
    z[i] = 0;
}

z[1] = 5;

f(z, A, B);

for (i = 0; i < ARRAY_SIZE; i++)
    printf("z is %.16Le\n", z[i]);



free(z);
z = NULL;

end = clock();
printf("Took %ld ticks\n", end-start);
printf("Took %f seconds\n", (double)(end-start)/CLOCKS_PER_SEC);



return 0;  
}  

void f(long double fb[], long double fA, long double fB) {
    fb[0] = fb[1]* fA;
    fb[1] = fb[1] - 1;
    return;
 }

Some errors with MVS2008:

testim.c(16) : error C2143: syntax error : missing ';' before 'const'  
testim.c(18) :error C2143: syntax error : missing ';' before 'type'  
testim.c(20) :error C2143: syntax error : missing ';' before 'type'   
testim.c(21) :error C2143: syntax error : missing ';' before 'type'    
testim.c(23) :error C2065: 'z' : undeclared identifier   
testim.c(23) :warning C4047: '==' : 'int' differs in levels of indirection from 'void *'  
testim.c(28) : error C2065: 'A' : undeclared identifier
testim.c(28) : warning C4244: '=' : conversion from 'double' to 'int', possible loss of data

and it goes to 28 errors. Note that I don't have any errors/warnings without your clock codes.

LATEST NEWS: I unfortunately didn't get a good reply here. But after a search on Google, the code is working. Here it is:

#include <stdio.h>
#include <stdlib.h>
#include <math.h>
#include <time.h>


void f(long double fb[], long double fA);

int main() {

clock_t start = clock();


const int ARRAY_SIZE = 11;

long double* z = (long double*) malloc(sizeof (long double) * ARRAY_SIZE);

int i;
long double A;

if (z == NULL) {
printf("Out of memory\n");
exit(-1);
}

A = 0.5;


for (i = 0; i < ARRAY_SIZE; i++) {
z[i] = 0;
}

z[1] = 5;

f(z, A);

for (i = 0; i < ARRAY_SIZE; i++)
printf("z is %.16Le\n", z[i]);



free(z);
z = NULL;

printf("Took %f seconds\n", ((double)clock()-start)/CLOCKS_PER_SEC);



return 0;
}

void f(long double fb[], long double fA) {
fb[0] = fb[1]* fA;
fb[1] = fb[1] - 1;
return;
}

Cheers

Update on April 10: Here's a better solution thanks to "JustJeff"

#include <windows.h>
#include <stdio.h>
#include <stdlib.h>

void f(long double fb[], long double fA);

const int ARRAY_SIZE = 11;

int main(void)
{

   long double* z = (long double*) malloc(sizeof (long double) * ARRAY_SIZE);
   int i;
   long double A;

   LARGE_INTEGER freq;
   LARGE_INTEGER t0, tF, tDiff;
   double elapsedTime;
   double resolution;

   if (z == NULL) {
   printf("Out of memory\n");
   exit(-1);
   }
   QueryPerformanceFrequency(&freq);
   QueryPerformanceCounter(&t0);
   // code to be timed goes HERE
   {
    A = 0.5;


    for (i = 0; i < ARRAY_SIZE; i++) {
    z[i] = 0;
    }

    z[1] = 5;
    f(z, A);


    for (i = 0; i < ARRAY_SIZE; i++)
    printf("z is %.16Le\n", z[i]);

    free(z);
    z = NULL;

   }
QueryPerformanceCounter(&tF);
tDiff.QuadPart = tF.QuadPart - t0.QuadPart;
elapsedTime = tDiff.QuadPart / (double) freq.QuadPart;
resolution = 1.0 / (double) freq.QuadPart;
printf("Your performance counter ticks %I64u times per second\n", freq.QuadPart);
printf("Resolution is %lf nanoseconds\n", resolution*1e9);
printf("Code under test took %lf sec\n", elapsedTime);
return 0;
}


void f(long double fb[], long double fA) {
fb[0] = fb[1]* fA;
fb[1] = fb[1] - 1;
return;
}

It works both with MVS2008 and with Borland C++ builderX from 2003.

Solution

If you're on windows and you want to measure stuff down in the microseconds, investigate QueryPerformanceCounter() and QueryPerformanceFrequency(). On many systems these can resolve full processor clock periods, third of a nanosecond stuff, and I don't believe I've ever seen it any more coarse than 3.5795MHz, still well under a microsecond.

You call QueryPerformanceFrequency() to determine how many counts per second the counter counts. Then call QueryPerformanceCounter() before your code under test, and then again after. Delta the two readings of QPC and divide by the period from QPF and you get the elapsed time between the two QPC calls. Like so ...

LARGE_INTEGER freq;
LARGE_INTEGER t0, tF, tDiff;
double elapsedTime;
QueryPerformanceFrequency(&freq);
QueryPerformanceCounter(&t0);
// code to be timed goes HERE
QueryPerformanceCounter(&tF);
tDiff.QuadPart = tF.QuadPart - t0.QuadPart;
elapsedTime = tDiff.QuadPart / (double) freq.QuadPart;
// elapsedTime now has your measurement, w/resolution given by freq

Evidently these access a hardware counting device that is tied to some system oscillator on the main board, in which case they shouldn't suffer jitter from software load. The resolution you get depends on your system.

FOLLOW UP

Here's a very simple complete program that demonstrates the interface:

#include <windows.h>
int main(void)
{
    LARGE_INTEGER freq;
    LARGE_INTEGER t0, tF, tDiff;
    double elapsedTime;
    double resolution;
    QueryPerformanceFrequency(&freq);
    QueryPerformanceCounter(&t0);
    // code to be timed goes HERE
    {
        Sleep(10);
    }
    QueryPerformanceCounter(&tF);
    tDiff.QuadPart = tF.QuadPart - t0.QuadPart;
    elapsedTime = tDiff.QuadPart / (double) freq.QuadPart;
    resolution = 1.0 / (double) freq.QuadPart;
    printf("Your performance counter ticks %I64u times per second\n", freq.QuadPart);
    printf("Resolution is %lf nanoseconds\n", resolution*1e9);
    printf("Code under test took %lf sec\n", elapsedTime);
    return 0;
}

For something as simple as this, it's quicker to skip the IDE, just save it in a foo.c file and (assuming MS VS 2008) use the command line

cl foo.c

to build it. Here's the output on my system:

Your performance counter ticks 3579545 times per second
Resolution is 279.365115 nanoseconds
Code under test took 0.012519 sec