Thread: Displaying Function Run Time

The trouble is that standard C functions like time() and clock() do not have very good precision, as you have discovered. Sometimes 1/18.2 of a second accuracy; sometimes only 1 second accuracy.

To get higher granularity, try Windows functions like QueryPerformaceCounter(). (I think that's the one.) http://support.microsoft.com/kb/q172338/

[edit] Example:

Code:

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

LARGE_INTEGER stime;

void start_time(void);
long end_time(void);

int main(int argc, char *argv[]) {
    char *call = 0, *p;
    size_t lcall = 0, len;
    int x;

    if(argc <= 1) {
        printf("\nusage: timeit command_to_time [args]\n");
        return 1;
    }

    for(x = 1; x < argc; x ++) {
        len = strlen(argv[x]);

        p = realloc(call, lcall+len+1 + (x+1 < argc ? 1 : 0));
        if(!p) {
            fprintf(stderr, "Out of memory\n");
            free(call);
            return 1;
        }
        call = p;

        strcpy(call+lcall, argv[x]);
        if(x+1 < argc) {
            call[lcall+len] = ' ';
            call[lcall+len+1] = 0;
            lcall ++;
        }

        lcall += len;
    }

    start_time();
    system(call);
    printf("&#37;li\n", end_time());

    free(call);

    return 0;
}

void start_time(void) {
    QueryPerformanceCounter(&stime);
}

long end_time(void) {
    LARGE_INTEGER diff;
    LARGE_INTEGER freq;

    QueryPerformanceCounter(&diff);
    diff.QuadPart -= stime.QuadPart;
    diff.QuadPart *= 1000;  /* Adjust to milliseconds, shouldn't overflow */
    QueryPerformanceFrequency(&freq);

    return (long)(diff.QuadPart / freq.QuadPart);
}

That's a Windows program I wrote a long time ago to time how long any arbitrary command takes to execute. It's not very well coded. (Note the missing <string.h>.) The times also do not take into account how slow system() is, but it's an okay example. Just ignore everything in main(). [/edit]