Thread: Please Help with C code regarding time.h functions and FILE readings

Hi everyone,

What I am trying to do is to read in a file, line by line, and write to a new file until the EOF. I also want to find out the time it takes for the program to run, one for CPU and one for real world time. My code is kind of a mess right now so I can use some help. Much appreciated.

Code:

#include <stdio.h>
#include <time.h>
#include <string.h>




int main(void)
{
    clock_t begin, finish;
    double time_spent;
    
    
    
    time_t start, end;
    double duration = 0;
    
    begin = clock();
    
    time(&start);
    
    FILE *fpr, *fpw;
    
    char file_name_r[]="";
    char file_name_w[]="";
    char string[BUFSIZ];
 
    
    printf( "\nEnter the name of the file to write to: " );
    scanf("%s", &file_name_w);
    
    printf( "Enter the name of the file to open: " );
    scanf("%s", &file_name_r);
    
    
    fpr = fopen(file_name_r, "r");
    
    if(fpr == NULL)
    {
        printf( "\n%s\ File NOT FOUND!",file_name_r);
    }
    
    while (fgets(string, sizeof string, fpr) != NULL){
        
        fpw = fopen(file_name_w, "w");
        fprintf(fpw, "%s", string);
        
    }
    
        
    fclose(fpr);
    fclose(fpw);
    
    return 0;
    
    end = clock();
    
    time_spent = (double)(finish - begin) / CLOCKS_PER_SEC;
    printf("Time elapsed in CPU milli-seconds : %f milli-seconds/n", time_spent);
    
    
    
    time(&end);
    
    duration = difftime(end, start);
    duration = duration/1000;
    printf("Time elapsed in Wall-clock : %f milli-seconds\n", duration);
    
    
}

Thanks for the reply whiteflags,

I updated my code based on your comments.

My concerns would be:

Is my file reading code correct and does what I intended?

Is the placement of the start time and end time functions in the right place. One to calculate the time the program uses the CPU and one from the start of program to the end of program.

Also, I am not sure where to put the txt files, or should I include the path to the file somewhere in the code?

Thanks a whole bunch guys!

Code:

#include <stdio.h>
#include <time.h>
#include <string.h>




int main(void)
{
    clock_t begin, finish;
    double time_spent;
    
    
    
    time_t start, end;
    double duration = 0;
    
    begin = clock();
    
    time(&start);
    
    FILE *fpr, *fpw;
    
    char file_name_r[100]="";
    char file_name_w[100]="";
    char string[BUFSIZ];
 
    
    printf( "\nEnter the name of the file to write to: " );
    scanf("%s", file_name_w);
    
    printf( "Enter the name of the file to open: " );
    scanf("%s", file_name_r);
    
    
    fpr = fopen(file_name_r, "r");
    
    if(fpr == NULL)
    {
        printf( "\n%s File NOT FOUND!",file_name_r);
    }
    
    fpw = fopen(file_name_w, "w");

    while (fgets(string, sizeof string, fpr) != NULL){
        
        fprintf(fpw, "%s", string);
        
    }
    
        
    fclose(fpr);
    fclose(fpw);
    
    return 0;
    
    end = clock();
    
    time_spent = (double)(finish - begin) / CLOCKS_PER_SEC;
    printf("Time elapsed in CPU milli-seconds : %f milli-seconds/n", time_spent);
    
    
    
    time(&end);
    
    duration = difftime(end, start);
    duration = duration/1000;
    printf("Time elapsed in Wall-clock : %f milli-seconds\n", duration);
    
    
}

I appreciate all the help on this. I updated the start time to right before the read file opened and the end right after both files closed. Also placed return 0; as the last line in the code.

I will try to test this with the files in place.

Thanks a lot guys

I'm not sure that what you test will actually give you two different times at all, either (or, at least, they will always return two times which - to within their accuracy - always differ by exactly the same amount, irrespective of the time taken or the size of the files copied).

What makes you think that you're measuring "CPU time" versus "real-world time"? clock() returns the number of clock ticks elapsed, and time() the number of seconds elapsed and as you can see they will be very closely correlated by the CLOCK_PER_SEC fixed ratio anyway. I don't think you're measuring what you think you are, and if you're after total CPU time used rather than clock time (i.e. trying to get an impression of I/O time, etc.) then you're really out of luck with standard C unless you use a machine-specific library or function to do that job for you. "clock" is representative of little in modern machines because they don't run at constant ticks per seconds, and even when they used to, that number was never representative anyway (i.e. some things take more ticks to execute than others anyway).

All you've done is made two time measurements of different accuracy of slightly different portions of your program whose answers will hardly, if ever, vary from each other.