github.com/afumu/libc@v0.0.6/musl/src/stdio/vswprintf.c (about)

     1  #include "stdio_impl.h"
     2  #include <limits.h>
     3  #include <errno.h>
     4  #include <stdint.h>
     5  #include <stdlib.h>
     6  #include <wchar.h>
     7  
     8  struct cookie {
     9  	wchar_t *ws;
    10  	size_t l;
    11  };
    12  
    13  static size_t sw_write(FILE *f, const unsigned char *s, size_t l)
    14  {
    15  	size_t l0 = l;
    16  	int i = 0;
    17  	struct cookie *c = f->cookie;
    18  	if (s!=f->wbase && sw_write(f, f->wbase, f->wpos-f->wbase)==-1)
    19  		return -1;
    20  	while (c->l && l && (i=mbtowc(c->ws, (void *)s, l))>=0) {
    21  		s+=i;
    22  		l-=i;
    23  		c->l--;
    24  		c->ws++;
    25  	}
    26  	*c->ws = 0;
    27  	if (i < 0) {
    28  		f->wpos = f->wbase = f->wend = 0;
    29  		f->flags |= F_ERR;
    30  		return i;
    31  	}
    32  	f->wend = f->buf + f->buf_size;
    33  	f->wpos = f->wbase = f->buf;
    34  	return l0;
    35  }
    36  
    37  int vswprintf(wchar_t *restrict s, size_t n, const wchar_t *restrict fmt, va_list ap)
    38  {
    39  	int r;
    40  	unsigned char buf[256];
    41  	struct cookie c = { s, n-1 };
    42  	FILE f = {
    43  		.lbf = EOF,
    44  		.write = sw_write,
    45  		.lock = -1,
    46  		.buf = buf,
    47  		.buf_size = sizeof buf,
    48  		.cookie = &c,
    49  	};
    50  
    51  	if (!n) {
    52  		return -1;
    53  	} else if (n > INT_MAX) {
    54  		errno = EOVERFLOW;
    55  		return -1;
    56  	}
    57  	r = vfwprintf(&f, fmt, ap);
    58  	sw_write(&f, 0, 0);
    59  	return r>=n ? -1 : r;
    60  }