source: mainline/uspace/lib/libc/generic/io/vsnprintf.c@ 2e4bd1f

/*
 * 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.
 */

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

#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 */
};

/** Write string to given buffer.
 * Write at most data->size characters including trailing zero. According to C99
 * has snprintf to return number of characters that would have been written if
 * enough space had been available. Hence the return value is not number of
 * really printed characters but size of input string. Number of really used
 * characters is stored in data->len.
 *
 * @param str           Source string to print.
 * @param count         Size of the source string.
 * @param data          Structure with destination string, counter of used space
 *                      and total string size.
 * @return              Number of characters to print (not characters really
 *                      printed!)
 */
static 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;   
}

/** Print formatted to the given buffer with limited size.
 * @param str           Buffer.
 * @param size          Bffer size.
 * @param fmt           Format string.
 * \see For more details about format string see printf_core.
 */
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);
}

/** @}
 */