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Addressing Keyboard Buffer Limitations in C Programming

This technical overview examines keyboard buffer handling in C programming, particularly in light of unexpected situations like a cat on the keyboard. It discusses initial code examples with fixed buffer sizes and suggests modifications to ensure robust buffer management. We explore options for increasing buffer capacity, highlight potential pitfalls in buffer indexing, and recommend best practices for managing screen dimensions in relation to hardware updates. This guide is essential for developers looking to enhance their code resilience against unforeseen input scenarios.

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Addressing Keyboard Buffer Limitations in C Programming

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  1. #defineJan. 30, 2004 15-410“Don't make me stop the car...” • Dave Eckhardt • Bruce Maggs L09a_define

  2. Outline • What's wrong with this picture?

  3. Example 1 int scanbuf[64]; int getchar(void) { ... if (++bufindex == 64) bufindex = 0; ... }

  4. Example 1 – Change Requirement From: Dave Eckhardt Subject: keyboard buffer size Keyboard buffers must handle somebody placing a cat on the keyboard (the 101-key keyboard).

  5. Option 1 int scanbuf[256]; int getchar(void) { ... if (++bufindex == 64) bufindex = 0; ... }

  6. Option 2 int scanbuf[64]; int getchar(void) { ... if (++bufindex == 256) bufindex = 0; ... }

  7. Option 3 – Try This At Home!!! #define KSB_SIZE 256 int scanbuf[KSB_SIZE]; int getchar(void) { ... if (++bufindex == KSB_SIZE) bufindex = 0; ... }

  8. Example 2 int scanbuf[64]; int getchar(void) { ... if (bufindex == 63) bufindex = 0; ... }

  9. Example 2 – Truly Pernicious • How to fix half of the problem % grep 64 *.c • Wrong two ways • Won't find 63 • Will find other 64's

  10. Example 3 #define CENTER_X 49 #define CENTER_Y 12 ... set_cursor_pos(CENTER_Y, CENTER_X); ...

  11. Example 3 – Change Requirement From: Dave Eckhardt Subject: new screen size We have updated the VGA hardware initialization sequence. The new screen size will be: #define CONSOLE_WIDTH 120 #define CONSOLE_HEIGHT 30

  12. Example 4 ... p->regsave[-18] |= 0x402; ... • Don't make me stop the car......

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