C Function to Validate ISO 8601 Date Formats Using ‘strptime’

Posted by Derek@TheDailyLinux in Programming » Add Comment » 

Here’s a demonstration of how to use strptime and a list of format strings to validate, for example, a supplied ISO 8601 date in C or C++. You can play with the code below over at https://ideone.com/4Em3v1. It’s not an extensive list of all ISO 8601 dates, but these are the ones that work within a MySQL query. One improvement that could be made is to handle timezones in datetime strings like ’2010-01-01T01:01:01-7:00' and potentially micro seconds (if possible).

This is also a good demonstration for how to easily loop through all elements in an array of undefined size in C.

#define _GNU_SOURCE#include #include #include static intis_valid_iso8601_date_value(char *in){ struct tm result; char **f; char *ret; char *formats[] = { "%Y", "%Y-%m", "%y-%m", "%Y-%m-%d", "%y-%m-%d", "%Y%m%d", "%y%m%d", "%Y-%m-%d %T", "%y-%m-%d %T", "%Y%m%d%H%M%S", "%y%m%d%H%M%S", "%Y-%m-%dT%T", "%y-%m-%dT%T", "%Y-%m-%dT%TZ", "%y-%m-%dT%TZ", "%Y-%m-%d %TZ", "%y-%m-%d %TZ", "%Y%m%dT%TZ", "%y%m%dT%TZ", "%Y%m%d %TZ", "%y%m%d %TZ", NULL }; memset(&result, 0, sizeof(result)); for (f = formats; f && *f; f++) { ret = strptime(in, *f, &result); if (ret && *ret == '\0') return 1; } return 0;}int main(void) {char date_str[] = "2010-01-01T01:01:01Z"; if (is_valid_iso8601_date_value(date_str)) { printf("%s is a valid iso8601 date!", date_str); return 0; } else { printf("%s is not a valid iso8601 date!", date_str);return 1; }}

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