{"id":5805,"date":"2023-03-25T00:01:12","date_gmt":"2023-03-25T07:01:12","guid":{"rendered":"https:\/\/c-for-dummies.com\/blog\/?p=5805"},"modified":"2023-03-18T09:55:20","modified_gmt":"2023-03-18T16:55:20","slug":"hang-on-a-sec-part-ii","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=5805","title":{"rendered":"Hang On a Sec, Part II"},"content":{"rendered":"

The old days are gone, and with them the practice of using a for<\/em> loop as a timing delay. Loops still do pause program execution, with the question being how long does it take a computer to wait for a loop?
\n
\nPicking up from last week’s Lesson<\/a>, I need to know how many steps a loop needs to emulate those old days and pause program execution for about one second. I could just guess, starting with one million or so, but last Lesson I chose to use the computer’s clock to help me.<\/p>\n

The final code presented last week used the epoch value returned from the time()<\/em> function to monitor a flip from one second to the next. As the epoch value represents seconds, this approach seems good enough to present a situation where the computer can count away during the loop and report the count value. Here is the update to last week’s code:<\/p>\n

2023_03_25-Lesson-a.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n#include <time.h>\r\n\r\nint main()\r\n{\r\n    time_t now,then;\r\n    long count;\r\n\r\n    \/* obtain clock tick Epoch value *\/<\/span>\r\n    time(&now);\r\n\r\n    \/* pause one second *\/<\/span>\r\n    then = now;\r\n    while(then==now)\r\n        time(&now);\r\n    \/* now a new second has begun\r\n       start the next \"full second\" loop *\/<\/span>\r\n    then = now;\r\n    count = 0;\r\n    while(then==now)\r\n    {\r\n        count++;\r\n        time(&now);\r\n    }\r\n    printf(\"Cycles: %ld\\n\",count);\r\n\r\n    return(0);\r\n}<\/pre>\n
New to this version of the code is the declaration of long<\/em> variable count<\/code>. It’s initialized to zero at Line 19. Within the second while<\/em> loop, count<\/code> is incremented.<\/p>\n
Gone are the two printf()<\/em> statements that output the clock tick values. A single printf()<\/em> statement at Line 25 outputs the number of cycles (the value of variable count<\/code>) processed during the one-second loop. On my computer, I see this result:<\/p>\n
Cycles: 377291420<\/code><\/p>\n
The next step is to write a program that uses this value in a for<\/em> loop to attempt to pause execution for one second. Here is the code I wrote:<\/p>\n
2023_03_25-Lesson-b.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n\r\nint main()\r\n{\r\n    long delay;\r\n\r\n    \/* pause one second *\/<\/span>\r\n    for( delay=0; delay<377291420; delay ++ )\r\n        ;\r\n\r\n    return(0);\r\n}<\/pre>\n
I could have used a while<\/em> loop, but for<\/em> loops are how I wrote code way back when. No output is needed. Instead, I use the command line time<\/em> utility to see how long the program (a.out<\/code>) takes to run:<\/p>\n
$ time .\/a.out<\/p>\n
real    0m0.640s
\nuser    0m0.633s
\nsys     0m0.000s<\/code><\/p>\n
Rather than a full second, the code took 0.64 seconds to run — far less than what I hoped. Bummer.<\/p>\n
Then I remembered something important: The original program that counted the loop’s iterations also called the time()<\/em> function. Adding that call adds to the delay. To more accurately pause a second, the for<\/em> loop should also call the time()<\/em> function, as shown in this update:<\/p>\n
2023_03_25-Lesson-c.c<\/a><\/h3>\n
\r\n#include <stdio.h>\r\n#include <time.h>\r\n\r\nint main()\r\n{\r\n    long delay;\r\n\r\n    \/* pause one second *\/<\/span>\r\n    for( delay=0; delay<377291420; delay ++ )\r\n        time(NULL);\r\n\r\n    return(0);\r\n}<\/pre>\n
The time()<\/em> function requires an argument, which is set as NULL<\/code>. Also, the time.h<\/code> header is required. Duh.<\/p>\n
Here is the result when the program is run from the time<\/em> utility:<\/p>\n
$ time .\/a.out<\/p>\n
real    0m0.944s
\nuser    0m0.937s
\nsys     0m0.001s<\/code><\/p>\n
The value 0.944 is much closer to one second, which I’m flagging as a success.<\/p>\n
Then again, it’s not really a success. Running these delay programs on an older PC yielded a cycles value of 6,686,683 — far less than 377,291,420 on my main, fast computer. So the final program, the one that supposedly takes one second to run, takes nearly a minute to run on that older PC! Hopefully you can see why using a delay loop on a modern computer shouldn’t be a thing any more.<\/p>\n","protected":false},"excerpt":{"rendered":"
Writing a loop that pauses exactly one second – on my computer. Continue reading →<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"open","ping_status":"closed","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[2],"tags":[],"class_list":["post-5805","post","type-post","status-publish","format-standard","hentry","category-main"],"_links":{"self":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5805","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=5805"}],"version-history":[{"count":4,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5805\/revisions"}],"predecessor-version":[{"id":5823,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/5805\/revisions\/5823"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=5805"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=5805"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=5805"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}