ssfrr/oop-in-c

author: Spencer Russell comments: true title: A Gentle Introduction to Object-Oriented C Status: draft

Let's say we are creating a simple module for UART communication. The exact semantics of the hardware aren't important, but let's assume we have the registers:

• TXD will send a byte out when you write to it
• RXD which contains the last byte received
• STATUS has bit flags for TXDFULL (0x01)
• RXDFULL (0x02) which indicated whether there's new (unsent or unread) data in the respective registers.

Let's start with a first pass

UART.h

void writeByte(unsigned char outByte);
unsigned char readByte(void);

UART.c

#include "UART.h"
#include "registers.h" // assume this has our register definitions

#define TXDFULL 0x01
#define RXDFULL 0x02

void writeByte(unsigned char outByte) {
    // block until we're ready to send another byte
    while(STATUS & TXDFULL) {
    }
    TXD = outByte;
}

unsigned char readByte(void) {
    // block until there's new data received
    while(!(STATUS & RXDFULL) {
    }
    return RXD;
}

main.c

#include "UART.h"

int main(void) {
    const unsigned char outData[] = "Hello, World!\n";
    const unsigned char *idx = outData;

    while(idx) {
          writeByte(*idx++);
    }
    return 0;
}