vsnprintf.c

Go to the documentation of this file.

/*
 * Copyright (C) 2006 Josef Cejka
 * 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.
 */

#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <io/printf_core.h>


struct vsnprintf_data {
        size_t size; /* total space for string */
        size_t len; /* count of currently used characters */
        char *string; /* destination string */
};

int vsnprintf_write(const char *str, size_t count, struct vsnprintf_data *data);

int vsnprintf_write(const char *str, size_t count, struct vsnprintf_data *data)
{
        size_t i;
        i = data->size - data->len;

        if (i == 0) {
                return count;
        }
        
        if (i == 1) {
                /* We have only one free byte left in buffer => write there trailing zero */
                data->string[data->size - 1] = 0;
                data->len = data->size;
                return count;
        }
        
        if (i <= count) {
                /* We have not enought space for whole string with the trailing zero => print only a part of string */
                        memcpy((void *)(data->string + data->len), (void *)str, i - 1);
                        data->string[data->size - 1] = 0;
                        data->len = data->size;
                        return count;
        }
        
        /* Buffer is big enought to print whole string */
        memcpy((void *)(data->string + data->len), (void *)str, count);
        data->len += count;
        /* Put trailing zero at end, but not count it into data->len so it could be rewritten next time */
        data->string[data->len] = 0;

        return count;   
}

int vsnprintf(char *str, size_t size, const char *fmt, va_list ap)
{
        struct vsnprintf_data data = {size, 0, str};
        struct printf_spec ps = {(int(*)(void *, size_t, void *))vsnprintf_write, &data};

        /* Print 0 at end of string - fix the case that nothing will be printed */
        if (size > 0)
                str[0] = 0;
        
        /* vsnprintf_write ensures that str will be terminated by zero. */
        return printf_core(fmt, &ps, ap);
}

---