Writing a function in C that times an operation

This is a discussion on Writing a function in C that times an operation within the C Programming forums, part of the General Programming Boards category; So fat I have done this... Code: time_t t0, t1; Code: t1 = time(NULL); printf ("Operation took %f seconds\n",(c1 - ...

  1. #1
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    Writing a function in C that times an operation

    So fat I have done this...


    Code:
    time_t  t0, t1;
    Code:
    t1 = time(NULL);
    printf ("Operation took %f seconds\n",(c1 - c0)/CLOCKS_PER_SEC);
    The problem is that more often that not, it will just return 0.00000, even though the operation has obviously taken much longer, am I doing something wrong?

  2. #2
    Frequently Quite Prolix dwks's Avatar
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    You need to use difftime instead of subtracting time_ts, because subtraction isn't guarenteed to work.
    Code:
    #include <stdio.h>
    #include <time.h>  /* required */
    
    int main(void) {
        time_t s = time(0);
    
        long_task();
    
        printf("That took %f seconds.\n", (double)difftime(s, time(0))/CLOCKS_PER_SEC);
    
        return 0;
    }
    The args to difftime might be reversed.
    dwk

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    Thanks for that, but its still outputting 0.000 seconds.

  4. #4
    The Richness... Richie T's Avatar
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    ya that doesnt work for me, shouldn't use time (0), - i'm not getting zero but im getting a much smaller number than i should. the faq has a better solution which i've used myself before -

    http://faq.cprogramming.com/cgi-bin/...&id=1043284392

    if you are getting 0.000, it might have something to do with not having any actual work done from when you start the timer to when you calculate the difference. the problem with the dwks solution is that time (0) is only changing every second... the faq uses processor ticks.
    No No's:
    fflush (stdin); gets (); void main ();


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  5. #5
    and the hat of wrongness Salem's Avatar
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    difftime() returns a double, so there is no need for the cast
    difftime() returns the answer in seconds, so there is no need for the division.

  6. #6
    Frequently Quite Prolix dwks's Avatar
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    the problem with the dwks solution is that time (0) is only changing every second... the faq uses processor ticks.
    Well, not once a second, but it doesn't make for very accurate timing.
    Dev-Cpp/MS VS C++ 6.0, Windows XP
    I got a Win32 function that counts milliseconds to work under Dev-C++ . . . I don't remember the functions' names (there are two of them), but if you're interested I'll tell you next time I'm online.
    dwk

    Seek and ye shall find. quaere et invenies.

    "Simplicity does not precede complexity, but follows it." -- Alan Perlis
    "Testing can only prove the presence of bugs, not their absence." -- Edsger Dijkstra
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    and the hat of wrongness Salem's Avatar
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    Strange, using the example, I ALWAYS get 2293.672000 seconds no matter what operation I do.

  9. #9
    The Richness... Richie T's Avatar
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    using the faq or dwks?
    No No's:
    fflush (stdin); gets (); void main ();


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    The FAQ.

  11. #11
    The Richness... Richie T's Avatar
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    that is more than unusual, its standard code to the best of my knowledge. what compiler are you using, it would be very strange that its the cause of the problem...
    No No's:
    fflush (stdin); gets (); void main ();


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    Example of fgets (); The FAQ, C/C++ Reference


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    I'm using Dev-C++

  13. #13
    and the hat of wrongness Salem's Avatar
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    You'd better post your code then - you can stub out the work if you want, but at least show us how you're calculating time.

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    Code:
    #include <stdio.h>
    #include <stdlib.h>
    #include <ctype.h>
    #include <string.h>
    #include <time.h>
    
    
    typedef struct N {
        char      x[20];
        struct N *next;
    } List;
    
    List *insertlist(char word[15], List * b)
    {
        List *c = calloc(1, sizeof(List));
        strcpy( c->x, word ); 
        c->next = b;
        return c;
    }
    
    
    
    int search(char *query,char *query1, List * z)
    {
        int x=0;
     
      printf( "\nSearching through List for query...\n");
      while (z != NULL) {
        
        if ( strcmp(z->x,query) == 0 ) {
          x++;
        }
        z = z->next;
      }
      if(x==0) {
              printf("\nSorry! Your word was not found in the document\n");
              }
              else
              {
      printf("\nThe word %s was found %d times.\n", query1,x);
      return 0;
    }
    }
    
    lowercase(char *word) {
    
    int n = strlen(word) + 1;
    int i;
    for(i=0;i<n;i++){
    word[i] = tolower(word[i]);
    }  
    }
    
    int main(int argc, char *argv[])
    {
      
        clock_t start, end;
        long count;
        char word[15];
        char query[15];
        char query1[15];
        int   x;  
        int   y; 
        int   c;     
        List *z = NULL; 
        
        FILE *fp;
        
       
      
     
         
        fp = fopen(argv[1], "r");
      
        c = 0;
        while ( (x = fgetc(fp)) != EOF) {
            if (isspace(x) || ispunct(x)) {
                word[c] = '\0';
               
              
               
                c = 0;
                lowercase(word);
                z = insertlist(word, z);
            } else {
                word[c] = x;
              
                c = c + 1;
            }
            
        }
       
    
        
        
        end = clock();
        printf ( "The interval was: %f seconds\n",
        (double)( start - end ) / (double)CLOCKS_PER_SEC );
    
    
        fclose(fp);
      
        printf("\nPlease enter a search query:");
        scanf("%s",query);
        strcpy(query1,query);
        lowercase(query);
        search(query,query1, z);
         
        
    
    
            
        return 0;   
    }
    Last edited by Wiretron; 01-28-2006 at 12:00 PM.

  15. #15
    and the hat of wrongness Salem's Avatar
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    So basically, you didn't initialise start at all, and you printed the answer BEFORE setting end?

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