source: mainline/libc/generic/io/vsnprintf.c@ 6180b57

/*
 * 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);

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

        if (i > 0) {
                if (i <= j) { 
                        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;
                        } else {
                                /* 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;
                        }
                } else {
                        /* Buffer is big enought to print whole string */
                        memcpy((void *)(data->string + data->len), (void *)str, j);
                        data->len += j;
                        /* 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)
{
        size_t retval;
        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);
}