I’m a new bike in C language, after some simple examples and best practices of how to use regular expressions in ANSI C.
I have simple test, want to get date in an description string bellow
“{d(02/01/2019)}-call Ms.ha check this case”. I mean want to get “02/01/2019”
this is my code

#include <stdint.h>
#include <stdio.h>
#include <stdlib.h>
#include <regex.h>

#define ARRAY_SIZE(arr) (sizeof((arr)) / sizeof((arr)[0]))
// initialize target string and regular expression string

int main(int argc, char **argv)
{
     regex_t preg;

        char *string = "{d(02/01/2019)}-call Ms.ha check this case";
        char *pattern="?[0-9]+(\/[0-9]+)+(\/[0-9]+)?"; // I'm stupid pattern in here.
        size_t nmatch = 2;
        regmatch_t pmatch[2];


        regcomp(&preg, pattern, REG_EXTENDED);
        regexec(&preg, string, nmatch, pmatch, 0);

        printf("a matched substring "%.*s" is found at position %d to %d.n",
         pmatch[1].rm_eo - pmatch[1].rm_so, &string[pmatch[1].rm_so],
         pmatch[1].rm_so, pmatch[1].rm_eo - 1);

        regfree(&preg);


        return EXIT_SUCCESS;
}

How to create pattern in this case,

Thanks Advice.