source: mainline/common/stdc/vsnprintf.c

/*
 * Copyright (c) 2006 Josef Cejka
 * Copyright (c) 2025 Jiří Zárevúcky
 * All rights reserved.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 *
 * - Redistributions of source code must retain the above copyright
 *   notice, this list of conditions and the following disclaimer.
 * - Redistributions in binary form must reproduce the above copyright
 *   notice, this list of conditions and the following disclaimer in the
 *   documentation and/or other materials provided with the distribution.
 * - The name of the author may not be used to endorse or promote products
 *   derived from this software without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
 * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 */

/** @addtogroup libc
 * @{
 */
/** @file
 */

#include <errno.h>
#include <macros.h>
#include <printf_core.h>
#include <stdarg.h>
#include <stdio.h>
#include <str.h>

typedef struct {
        char *dst;      /* Destination */
        size_t left;
} vsnprintf_data_t;

static int vsnprintf_str_write(const char *str, size_t size, void *data)
{
        vsnprintf_data_t *d = data;
        size_t left = min(size, d->left);
        if (left > 0) {
                memcpy(d->dst, str, left);
                d->dst += left;
                d->left -= left;
        }
        return EOK;
}

int vsnprintf(char *str, size_t size, const char *fmt, va_list ap)
{
        vsnprintf_data_t data = {
                .dst = str,
                .left = size ? size - 1 : 0,
        };

        printf_spec_t ps = {
                vsnprintf_str_write,
                &data
        };

        int written = printf_core(fmt, &ps, ap);
        if (written < 0)
                return written;

        /* Write the terminating NUL character. */
        if (size > 0)
                data.dst[0] = 0;

        return written;
}

/** @}
 */