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

// crappy example
char *new_ctime_r(const time_t * timep, char *buf, int buflen)
{
    if (buflen < 26)
        return NULL;
    return ctime_r(timep, buf);
}


// function called in a multi-threaded application
void printtime()
{
    int buflen = 0;
    char *ptr, *output;
    time_t t;

    t = time(NULL);

    // ctime converts a time_t value to string
    // ctime_r is the re-entrant version of ctime

    do {
        buflen = buflen * 2 + 1;
        output = alloca(buflen);
    }
    while ((ptr = new_ctime_r(&t, output, buflen)) == NULL);

    printf("%d bytes was allocated at %p\n", buflen, output);
    printf("The datetime is %s", ptr);
}

int main()
{
    printtime();
    return 0;
}