typedef struct lts_LoadState
{
  const unsigned char * pos;
  size_t unread;
} lts_LoadState;

使用this simple API访问缓冲区：

/* Initialize buffer */
void ltsLS_init(lts_LoadState * ls,const unsigned char * data,size_t len);

/* Do we have something to read? (Actually a macro.) */
BOOL ltsLS_good(ls);

/* How much do we have to read? (Actually a macro.) */
size_t ltsLS_unread(ls);

/* Eat given number of characters,return pointer to beginning of eaten data */
const unsigned char * ltsLS_eat(lts_LoadState * ls,size_t len);

注意：ltsLS_unread可以替换为return(ltsLS_good(ls))？ SIZE_MAX：0而不会破坏当前的实现.

此代码用于load some data in a custom format from a string buffer.(This可能是一个更好的例子.)

现在我需要不是从字符串缓冲区加载数据,而是从FILE指针加载数据.

我不想复制粘贴实现,而是希望重用现有代码. (当然,我可以重构/改编它.)

这是C语言中的教科书,但是如何在普通的C中做到这一点而不会产生运行时开销？

下面是一个使用lts_LoadState API并且不能进行复制粘贴的示例函数(当然,可以更改为支持字符串缓冲区和FILE *)：

static int ltsLS_readline(
    lts_LoadState * ls,const unsigned char ** dest,size_t * len
  )
{
  const unsigned char * origin = ls->pos;
  unsigned char last = 0;
  size_t read = 0;

  while (ltsLS_good(ls))
  {
    if (ltsLS_unread(ls) > 0)
    {
      unsigned char b = *ls->pos; /* OK,this should be ltsLS_eat_char macro. */
      ++ls->pos;
      --ls->unread;

      if (b == '\n')
      {
        *dest = origin;
        *len = (last == '\r') ? read - 1 : read;

        return LUATEXTS_ESUCCESS;
      }

      last = b;
      ++read;
    }
    else
    {
      ls->unread = 0;
      ls->pos = NULL;
    }
  }

  return LUATEXTS_ECLIPPED;
}