Testing Waiting Characters in Java

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At first, in line 11, getch() carries on its normal blocking function. The program waits for a key to be pressed on the keyboard. (The key s value is unimportant, so it s not saved.) The nodelay() function in line 13 turns off getch() s blocking. Therefore, the while loop continues as long as getch() returns the value ERR, which is what it generates when no key has been pressed. During the while loop, values are displayed on the screen so that you re aware of the program continuing. Note that there is no need to restore getch() s function with another nodelay() function, at least not in this example.
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With getch() s waiting ability turned off, you can use getch() to filter through keys pressed on the keyboard and scan for only those you need, discarding the rest. For example, suppose you need to modify the KEYWAIT1.C program so that instead of any key stopping the insane loop, only the spacebar works to stop it. Try it! Modify the KEYWAIT1.C source code on your own. Change the code so that only the spacebar key stops the insane loop. There are many ways to do this, so be creative! If you ve done things properly, the program stops the loop only when the spacebar has been pressed. You can press other keys on the keyboard, and the program continues to loop; only the spacebar stops it. Listing 7-2 shows my solution, though it is only one of many.
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Listing 7-2: keywait2.c
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 #include <ncurses.h> int main(void) { int value = 0; initscr(); addstr( Press any key to begin:\n ); refresh(); getch(); nodelay(stdscr,TRUE); /* turn off getch() wait */ addstr( Press the Spacebar to stop the insane loop!\n ); while(1) { printw( %d\r ,value++);
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Listing 7-2 (continued)
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18 19 20 21 22 23 24 refresh(); if(getch() == ) break; } endwin(); return 0; }
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How to Implement kbhit()
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If you re an ancient DOS programmer or just familiar with the C language on the PC, you might remember (and reminisce about) the old kbhit() function. It was used to determine whether or not characters were waiting to be read from the keyboard buffer. kbhit() returned TRUE if characters were waiting, FALSE otherwise. You can use nodelay() and getch() in NCurses to emulate this behavior somewhat but not exactly. The problem is that getch() still fetches a key. So what you need is a way to take that key and stuff it back to the keyboard input queue. The function that handles that is called, logically, ungetch(). Here s the format:
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ungetch(ch)
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The ungetch() function places the character ch back into the input buffer. You can do this to pre-stuff characters if you like or to toss back characters when creating a kbhit()-like function, as shown in Listing 7-3.
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Listing 7-3: kbhit.c
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1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 #include <ncurses.h> int kbhit(void) { int ch,r; /* turn off getch() blocking and echo */ nodelay(stdscr,TRUE); noecho(); /* check for input */ ch = getch(); if( ch == ERR) r = FALSE; else { r = TRUE; ungetch(ch);
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/* no input */ /* input */
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Listing 7-3 (continued)
19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 } /* restore block and echo */ echo(); nodelay(stdscr,FALSE); return(r); } int main(void) { initscr();
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addstr( Press any key to end this program: ); while(!kbhit()) ; endwin(); return 0; }
And when you press a key, the program ends. Vo l , there is your kbhit() function equivalent. Of course, this function does assume that echo() is set and nodelay() is FALSE for the standard screen. It also assumes that the standard screen is the input screen. Adjust these items as needed for your own use, or just assume that kbhit() makes these assumptions and live with it.
N OT E See the section Silence, please! later in this chapter for more information on the echo() function.