Displaying Function Run Time

This is a discussion on Displaying Function Run Time within the C Programming forums, part of the General Programming Boards category; Hi, I'm a beginner C programming student, and I need to display a function's run time on the display console. ...

  1. #1
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    Displaying Function Run Time

    Hi, I'm a beginner C programming student, and I need to display a function's run time on the display console.

    I know my time-calculating algorithm works (because if I change the location for the start-end times, I get a good, realistic number).

    However, for my function, I keep on getting a display time of 0. How can I extend my precision to show how long my function takes?

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    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]
    Last edited by dwks; 03-21-2008 at 01:39 PM.
    dwk

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