{"id":3139,"date":"2018-06-09T00:01:07","date_gmt":"2018-06-09T07:01:07","guid":{"rendered":"http:\/\/c-for-dummies.com\/blog\/?p=3139"},"modified":"2018-06-02T12:37:21","modified_gmt":"2018-06-02T19:37:21","slug":"time-after-time","status":"publish","type":"post","link":"https:\/\/c-for-dummies.com\/blog\/?p=3139","title":{"rendered":"Time After Time"},"content":{"rendered":"

While writing some code recently, it became necessary to translate timestamp strings into time_t<\/em> or epoch time values. This value is the number of seconds that have ticked since midnight, January 1, 1970. time_t<\/em> values are stored long integers (generally), but I needed a utility to translate them into time strings. It turned out, such a tool wasn’t that difficult to create.
\n
\nHere is the code I wrote for a utility I call epoch<\/em>. It takes a command line time_t<\/em> value or, if not present, it prompts for one. The value is output as a time string.<\/p>\n

\r\n#include <stdio.h>\r\n#include <stdlib.h>\r\n#include <time.h>\r\n\r\nint main(int argc, char *argv[])\r\n{\r\n    time_t now;\r\n\r\n    \/* gather input *\/<\/span>\r\n    if(argc > 1)\r\n    {\r\n        now = atoi(argv[1]);\r\n    }\r\n    else\r\n    {\r\n        printf(\"Unix epoch time: \");\r\n        scanf(\"%ld\",&now);\r\n    }\r\n\r\n    printf(\"%s\",ctime(&now));\r\n\r\n    return(0);\r\n}<\/pre>\n
The code turned out to be much simpler than I thought: time_t<\/em> variable now<\/code> is declared at Line 7. If argv[1]<\/code> is present, it’s translated from a string into an int<\/em> value by the atoi()<\/em> function at Line 12. Otherwise, input is fetched at Line 17.<\/p>\n
Yes, I used scanf()<\/em> because it’s easy. And though a bogus value could be read, no potential for damage is made to the system by entering a bogus time_t<\/em> value; you just get bad output.<\/p>\n
The workhorse of the utility is the ctime()<\/em> function in the printf()<\/em> statement at Line 20, which outputs a time string.<\/p>\n
Here’s a sample run:<\/p>\n
.\/epoch 1528527600\r\nSat Jun  9 00:00:00 2018<\/code><\/pre>\n
The problem with the epoch <\/em>utility is that it doesn’t do you any good unless you know a time_t<\/em> value. You can guess at values, which is an interesting diversion, but instead of guessing, I wrote the now<\/em> utility. It generates the time_t<\/em> value for “right now.”<\/p>\n
\r\n#include <stdio.h>\r\n#include <time.h>\r\n\r\nint main()\r\n{\r\n        time_t now;\r\n\r\n        time(&now);\r\n        printf(\"%ld\\n\",now);\r\n\r\n        return(0);\r\n}<\/pre>\n
This code declares the time_t<\/em> variable now<\/code> at Line 6, then fills that value by using the time()<\/em> function at Line 8. The value, a long int<\/em>, is printed at Line 9. Simple enough, as is the output:<\/p>\n
.\/now\r\n1528527600<\/code><\/pre>\n
And, if you’re using a Unix shell, you can combine the two commands to output the current time:<\/p>\n
.\/epoch `.\/now`\r\nSat Jun  9 00:00:00 2018<\/code><\/pre>\n
Indeed, this code is silly stuff. Many utilities are silly, but their purpose greatly makes sense when you need them. In my case, I was working with time_t<\/em> values and needed a quick way to translate them. These two utilities, epoch<\/em> and now<\/em>, proved most helpful.<\/p>\n","protected":false},"excerpt":{"rendered":"
Here are some handy utilities that deal with Unix epoch time. 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-3139","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\/3139","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=3139"}],"version-history":[{"count":4,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/3139\/revisions"}],"predecessor-version":[{"id":3152,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=\/wp\/v2\/posts\/3139\/revisions\/3152"}],"wp:attachment":[{"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=3139"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=3139"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/c-for-dummies.com\/blog\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=3139"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}