text: #include "stdio_impl.h"
  #include <wchar.h>
  #include <errno.h>
  #include <limits.h>
  #include <string.h>
  
  struct cookie {
  	wchar_t **bufp;
  	size_t *sizep;
  	size_t pos;
  	wchar_t *buf;
  	size_t len;
  	size_t space;
  	mbstate_t mbs;
  };
  
  static off_t wms_seek(FILE *f, off_t off, int whence)
  {
  	ssize_t base;
  	struct cookie *c = f->cookie;
  	if (whence>2U) {
  fail:
  		errno = EINVAL;
  		return -1;
  	}
  	base = (size_t [3]){0, c->pos, c->len}[whence];
  	if (off < -base || off > SSIZE_MAX/4-base) goto fail;
  	memset(&c->mbs, 0, sizeof c->mbs);
  	return c->pos = base+off;
  }
  
  static size_t wms_write(FILE *f, const unsigned char *buf, size_t len)
  {
  	struct cookie *c = f->cookie;
  	size_t len2;
  	wchar_t *newbuf;
  	if (len + c->pos >= c->space) {
  		len2 = 2*c->space+1 | c->pos+len+1;
  		if (len2 > SSIZE_MAX/4) return 0;
  		newbuf = realloc(c->buf, len2*4);
  		if (!newbuf) return 0;
  		*c->bufp = c->buf = newbuf;
  		memset(c->buf + c->space, 0, 4*(len2 - c->space));
  		c->space = len2;
  	}
  	
  	len2 = mbsnrtowcs(c->buf+c->pos, (void *)&buf, len, c->space-c->pos, &c->mbs);
  	if (len2 == -1) return 0;
  	c->pos += len2;
  	if (c->pos >= c->len) c->len = c->pos;
  	*c->sizep = c->pos;
  	return len;
  }
  
  static int wms_close(FILE *f)
  {
  	return 0;
  }
  
  FILE *open_wmemstream(wchar_t **bufp, size_t *sizep)
  {
  	FILE *f;
  	struct cookie *c;
  	if (!(f=malloc(sizeof *f + sizeof *c))) return 0;
  	memset(f, 0, sizeof *f + sizeof *c);
  	f->cookie = c = (void *)(f+1);
  
  	c->bufp = bufp;
  	c->sizep = sizep;
  	c->pos = c->len = c->space = 0;
  	c->buf = 0;
  
  	f->flags = F_NORD;
  	f->fd = -1;
  	f->buf = (void *)(c+1);
  	f->buf_size = 0;
  	f->lbf = EOF;
  	f->write = wms_write;
  	f->seek = wms_seek;
  	f->close = wms_close;
  
  	if (!libc.threaded) f->lock = -1;
  
  	OFLLOCK();
  	f->next = libc.ofl_head;
  	if (libc.ofl_head) libc.ofl_head->prev = f;
  	libc.ofl_head = f;
  	OFLUNLOCK();
  
  	return f;
  }
  