#include <stdio.h>
#include <time.h>
 
int main(void)
{
    time_t     now;
    struct tm  *ts;
    char       buf[80];
 
    /* Some distant moment in the past */
    now = -10000000000;
 
    /* Format and print the time, "ddd yyyy-mm-dd hh:mm:ss zzz" */
    ts = localtime(&now);
    strftime(buf, sizeof(buf), "%a %Y-%m-%d %H:%M:%S %Z", ts);
    printf("%s\n", buf);
 
    /* Try to get the timestamp moment back */
 
    time_t now2 = mktime(ts);
 
    printf("%i\n", now2);
 
    return 0;
 
}
 
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Mon 1653-02-10 06:32:52 AMT
-1