clock using fflush is not clearing screen - c

Question

I am trying to make a clock in C, but the screen is not properly clearing, it just keeps printing to a new line. How am I improperly using fflush?
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
int main()
{
while (1) {
time_t rawtime;
struct tm * timeinfo;
time ( &rawtime );
timeinfo = localtime ( &rawtime );
printf ("%s", asctime (timeinfo));
fflush(stdout);
}
return 0;
}

Answer 1

This strips out the newline from the asctime string and then uses a return to push the cursor back to the start of line
#include <string.h>
int main()
{
while (1) {
time_t rawtime;
char st[30];
struct tm * timeinfo;
time ( &rawtime );
timeinfo = localtime ( &rawtime );
sprintf (st,"%s", asctime (timeinfo));
*(index(st,'\n'))='\0';
printf("\r%s",st);
flush(stdout);
sleep(1);
}
return 0;
}

Answer 2

This one has the advantage that it will work from the current location on the screen, no matter what that is. I added a label to print "The time is: " in order to show this. It does this by back spacing from the end of the time string rather than going to an absolute screen position or column. Caveat: The hack to get sleep() under Visual C has not been tried.
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#include <string.h>
#ifdef _MSC_VER
#include <windows.h>
#define sleep(T) Sleep((T) * 1000)
#else
#include <unistd.h>
#endif
int main(void)
{
char buf[42];
time_t the_time[1];
int i, len;
printf("The time is: ");
for (;;) {
time(the_time);
len = strlen(strcpy(buf, asctime(localtime(the_time)))) - 1;
printf("%.*s", len, buf);
for (i = 0; i < len; i++) putchar('\b');
fflush(stdout);
sleep(1);
}
return 0;
}

Answer 3

This will do it... (uses an evil windows call SetConsoleCursorPosition(), but does the trick)
#include <windows.h>
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
void gotoxy(int x, int y);
int main()
{
while (1) {
time_t rawtime;
struct tm * timeinfo;
gotoxy(0,0);//set to the upper left hand corner
time ( &rawtime );
timeinfo = localtime ( &rawtime );
printf ("%s", asctime (timeinfo));
fflush(stdout);
}
return 0;
}
void gotoxy(int x, int y)
{
COORD pos = {x, y};
HANDLE output = GetStdHandle(STD_OUTPUT_HANDLE);
SetConsoleCursorPosition(output, pos);
}
Try this for POSIX:
#!/usr/bin/tcc -run
#include <stdio.h>
#include <termios.h>
int main ()
{
struct termios ts0, ts1;
char cls [FILENAME_MAX];
FILE *f;
f = popen ("tput clear", "r");
fgets (cls, FILENAME_MAX, f);
pclose (f);
tcgetattr (0, &ts0);
ts1 = ts0;
ts1.c_lflag &= ~ECHO;
ts1.c_lflag &= ~ICANON;
tcsetattr (0, TCSAFLUSH, &ts1);
fputs (cls, stdout);
while (1) putchar (getchar ());
tcsetattr (0, TCSAFLUSH, &ts0);
return 0;
}