asprintf.c

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/*!
 * \file lib/gis/asprintf.c
 *
 * \brief GIS Library - GRASS implementation of asprintf().
 *
 * Eric G. Miller - Thu, 2 May 2002 17:51:54 -0700
 *
 * Rewritten by Glynn Clements, Sat, 6 Feb 2010
 * Assumes that vsnprintf() is available
 *
 * (C) 2002-2014 by the GRASS Development Team
 * (C) 2010 by Glynn Clements
 *
 * This program is free software under the GNU General Public License
 * (>=v2). Read the file COPYING that comes with GRASS for details.
 */

#define _GNU_SOURCE             /* enable asprintf */
#include <stdio.h>
#include <stdarg.h>
#include <string.h>
#include <grass/gis.h>

#ifndef G_asprintf

/**
 * \brief Safe replacement for <i>asprintf()</i>.
 *
 * Allocate a string large enough to hold the new output, including the 
 * terminating NULL, and return the number of characters printed. The 
 * pointer out is set to the output string and should be passed to 
 * <i>G_free()</i> to release the allocated storage when it is no longer 
 * needed.
 *
 * \param[out] out
 * \param[in] fmt
 * \param ap
 * \return number of bytes written
 */

int G_vasprintf(char **out, const char *fmt, va_list ap)
{
#ifdef HAVE_ASPRINTF
    return vasprintf(out, fmt, ap);
#else
    size_t size = strlen(fmt) + 50;
    char *buf = G_malloc(size);
    int count;

    for (;;) {
        /* BUG: according to man vsnprintf,
         * va_start() should be called immediately before vsnprintf(),
         * and va_end() immediately after vsnprintf()
         * otherwise there will be memory corruption */
        count = vsnprintf(buf, size, fmt, ap);
        if (count >= 0 && count < size)
            break;
        size *= 2;
        buf = G_realloc(buf, size);
    }

    buf = G_realloc(buf, count + 1);
    *out = buf;

    return count;
#endif /* HAVE_ASPRINTF */
}

int G_asprintf(char **out, const char *fmt, ...)
{
    va_list ap;
    int count;

    va_start(ap, fmt);
    count = G_vasprintf(out, fmt, ap);
    va_end(ap);

    return count;
}

#endif /* G_asprintf */

/**
 * \brief Reallocating version of <i>asprintf()</i>.
 *
 * Reallocate a string large enough to hold the output, including the 
 * terminating NULL, and return the number of characters printed.  
 * Contrary to <i>G_asprintf()</i>, any existing buffer pointed to by 
 * out of size osize is used to hold the output and enlarged if 
 * necessary. This is useful when <i>G_rasprintf</i> is called many 
 * times in a loop.
 *
 * \param[out] out
 * \param[out] osize
 * \param[in] fmt
 * \param ap
 * \return number of bytes written
 */

int G_rasprintf(char **out, size_t *size, const char *fmt, ...)
{
    va_list ap;
    int count;
    char *buf = *out;
    size_t osize = *size;

    if (osize < strlen(fmt) + 50) {
        osize = strlen(fmt) + 50;
        buf = G_realloc(buf, osize);
    }

    for (;;) {
        va_start(ap, fmt);
        count = vsnprintf(buf, osize, fmt, ap);
        va_end(ap);
        if (count >= 0 && count < osize)
            break;
        if (count > -1)
            osize = count + 1;
        else
            osize *= 2;
        
        buf = G_realloc(buf, osize);
    }

    *out = buf;
    *size = osize;

    return count;
}