OMG, ringbuffer in C macros :)

ringbuffer.h

#include <stdlib.h>
#include <memory.h>
#include <malloc.h>

#ifndef _ringbuffer_h
#define _ringbuffer_h

// semantics: buffer goes from start to end-1, start == end -> empty or full, see 'full' flag
#define ringBuffer_typedef(T, NAME) \
  typedef struct { \
    int count; \
    int size; \
    int start; \
    int end; \
    bool full; \
    T* elems; \
  } NAME

#define ringBufferInit(BUF_PTR, BUF_LENGTH, BUF_ENTRY_TYPE, BUF_TYPE) \
  assert(BUF_LENGTH > 0); \
  BUF_TYPE t; \
  BUF_PTR = &t; \
  BUF_PTR->size = BUF_LENGTH; \
  BUF_PTR->count = 0; \
  BUF_PTR->start = 0; \
  BUF_PTR->end = 0; \
  BUF_PTR->full = false; \
  BUF_PTR->elems = (BUF_ENTRY_TYPE*)malloc(BUF_PTR->size * sizeof(BUF_ENTRY_TYPE)); \
  memset(BUF_PTR->elems, 0, BUF_PTR->size * sizeof(BUF_ENTRY_TYPE))


#define ringBufferDestroy(BUF) free(BUF->elems)
#define ringBufferNextStartIndex(BUF) ((BUF->start + 1) % BUF->size)
#define ringBufferNextEndIndex(BUF) ((BUF->end + 1) % BUF->size)
#define ringBufferIsEmpty(BUF) (BUF->end == BUF->start && !BUF->full)
#define ringBufferIsFull(BUF) (BUF->full)

#define ringBufferReset(BUF, ELEM) \
  BUF->count = 0; \
  BUF->start = 0; \
  BUF->end = 0; \
  BUF->full = false

#define ringBufferWrite(BUF, ELEM) \
  BUF->elems[BUF->end] = ELEM; \
  BUF->end = ringBufferNextEndIndex(BUF); \
  if (!BUF->full) { \
    BUF->count++; \
    if (BUF->end == BUF->start) { \
      BUF->full = true; \
    } \
  } else { \
    BUF->start = ringBufferNextStartIndex(BUF); \
  }

#define ringBufferRead(BUF, I, ELEM) \
  assert(I < BUF->count); \
  ELEM = BUF->elems[(BUF->start + I) % BUF->size]

#define ringBufferForEach(BUF, item) \
    for(int keep = 1, \
            count = 0, \
            i = BUF->start;\
        keep && ((BUF->full) ? (count==0 || i != BUF->end) : i != BUF->end); \
        keep = !keep, i = (i + 1) % BUF->size, count++) \
      for(item = BUF->elems[i]; keep; keep = !keep)

#define ringBufferForEachRaw(BUF, item) \
    for(int keep = 1, \
            i = 0;\
        keep && i < BUF->size; \
        keep = !keep, i++) \
      for(item = BUF->elems[i]; keep; keep = !keep)

#endif

ringbufferTest.cpp

#include <SDKDDKVer.h>
#include <stdio.h>
#include <tchar.h>
#include <assert.h>

#include "lib/c-generic-ring-buffer/ringbuffer.h"

ringBuffer_typedef(int, IntBuffer);

void printIntBufferRaw(IntBuffer* buffer, char* message) {
  int item;
  printf("%s: (raw)[", message);
  ringBufferForEachRaw(buffer, item) {
    printf("%d ", item);
  }
  printf("]\n");
}

void printIntBufferNice(IntBuffer* buffer, char* message) {
  int item;
  printf("%s: [", message);
  ringBufferForEach(buffer, item) {
    printf("%d ", item);
  }
  printf("]\n");
}

void printIntBuffer(IntBuffer* buffer, char* message) {
  printIntBufferNice(buffer, message);
  printIntBufferRaw(buffer, message);
}

int _tmain(int argc, _TCHAR* argv[])
{
  // Declare vars.
  IntBuffer* myBuffer;

  ringBufferInit(myBuffer, 4, int, IntBuffer);

  printIntBuffer(myBuffer, "after init");
  ringBufferWrite(myBuffer, 1);
  printIntBuffer(myBuffer, "after 1 item");
  ringBufferWrite(myBuffer, 2);
  printIntBuffer(myBuffer, "after 2 items");
  ringBufferWrite(myBuffer, 3);
  printIntBuffer(myBuffer, "after 3 items");
  ringBufferWrite(myBuffer, 4);
  printIntBuffer(myBuffer, "after 4 items");

  int item;
  ringBufferRead(myBuffer, 0, item);
  printf("1st: %d\n", item);
  assert(item == 1);

  ringBufferRead(myBuffer, 1, item);
  printf("2nd: %d\n", item);
  assert(item == 2);

  ringBufferRead(myBuffer, 2, item);
  printf("3rd: %d\n", item);
  assert(item == 3);

  ringBufferRead(myBuffer, 3, item);
  printf("4th: %d\n", item);
  assert(item == 4);

  ringBufferWrite(myBuffer, 5);
  printIntBuffer(myBuffer, "after 5 items:");
  ringBufferWrite(myBuffer, 6);
  printIntBuffer(myBuffer, "after 6 items:");

  ringBufferRead(myBuffer, 2, item);
  assert(item == 5);
  ringBufferRead(myBuffer, 3, item);
  assert(item == 6);

  ringBufferDestroy(myBuffer);

  printf("All tests passed.\n");
  return 0;


	return 0;
}