c_cpp C中带有读指针的动态缓冲区示例

Posted 2021-05-14

#include <stdio.h>
#include <stdlib.h>


// C dynamic buffer with reader pointer.


// Macro to expand buffer.
#define Buf_EXPAND(buf, amount) \
        buf->cap += amount; \
        buf = realloc(buf, sizeof(Buf) + buf->cap)


typedef struct
{
  size_t len;
  size_t cap;
  unsigned char* reader;
  unsigned char data[0];
} Buf;

Buf* Buf_new(size_t reserve)
{
  Buf* newbuf = malloc(sizeof(Buf) + reserve);
  newbuf->len = 0;
  newbuf->cap = reserve;
  newbuf->reader = newbuf->data;
  return newbuf;
}

void Buf_print(Buf* b, int amount)
{
  while(amount--)
  {
    printf("%u\n", *(b->reader));
    b->reader++;
  }
}

// Checks if reader is at end
int Buf_reader_end(Buf* b)
{
  return b->reader == (b->data + b->cap);
}


int main(void) {
  Buf* c = Buf_new(10);
  printf("Reader @ = %p\n", c->reader);
  c->data[0] = 55;
  Buf_print(c, 2);
  printf("Reader moved = %lu\n", c->reader - c->data);
  printf("Reader is at end %d\n", Buf_reader_end(c));
  free(c);
  return 0;
}