Is there any function from time.h that sets internal buffer

Question

This is my code:

    int main() 
{
    time_t time1, time2;
    struct tm *timeinfo1, *timeinfo2;
    char *time1str, *time2str;


    time1 = 3600;
    time2 = 3720;

    // here i must insert function from time.h

    ///////////////////////////
    timeinfo1 = localtime(&time1);// here
    localtime(&time2);

    time1str = new char [strlen(asctime(timeinfo1)) + 2];
    strcpy(time1str, asctime(timeinfo1));
    timeinfo2 = localtime(&time2);
    time2str = asctime(timeinfo2);
    puts(time1str);
    puts(time2str);
    getchar();
    return 0;
}

Is there any function that i can insert between slash comments to set internal buffer.? This buffer erase my previous value.

Answer 1

Yes, there is. What you're looking for is the reentrant version of localtime() : localtime_r() . It works exactly like localtime() , except it writes its results into a buffer you supply as an argument instead of to a static buffer. The prototype is:

 struct tm *
 localtime_r(const time_t *clock, struct tm *result);

Usage in your application would look like:

struct tm timeinfo1, timeinfo2;
...
localtime_r(&time1, &timeinfo1);
localtime_r(&time2, &timeinfo2);

Answer 2

Since you tagged your question with C only. In C including C99 there was no such function. C11 now has a function localtime_s that is part of the optional bounds checking extension:

struct tm *localtime_s(const time_t * restrict timer, struct tm * restrict result);

Unfortunately, there are not many platforms that implement that extension yet.

POSIX has a localtime_r function with exactly the same interface and similar semantics. To capture this kind of system and remain portable you could do something like

#ifdef _XOPEN_SOURCE
# define localtime_s localtime_r
#endif

or if you want to have it closer to the additional guarantees that localtime_s is supposed to give

#ifdef _XOPEN_SOURCE
struct tm *localtime_s(const time_t * restrict timer, struct tm * restrict result) {
   return (timer && result ? localtime_r(timer, result) : 0);
}
#endif