u_truncate_printf.h

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// Copyright 2023, Collabora, Ltd.
// SPDX-License-Identifier: BSL-1.0
/*!
 * @file
 * @brief  Truncating versions of string printing functions.
 * @author Jakob Bornecrantz <jakob@collabora.com>
 * @ingroup aux_util
 */
 
#pragma once
 
#include "xrt/xrt_compiler.h"
 
#include <stdio.h>
#include <stdarg.h>
#include <limits.h>
 
 
#ifdef __cplusplus
extern "C" {
#endif
 
 
/*!
 * We want to truncate the value, not get the possible written.
 *
 * There are no version of the *many* Windows versions of this functions that
 * truncates and returns the number of bytes written (not including null). Also
 * need to have the same behaviour on Linux.
 *
 * @ingroup @aux_util
 */
static inline int
u_truncate_vsnprintf(char *chars, size_t char_count, const char *fmt, va_list args)
{
        /*
         * We always want to be able to write null terminator, and
         * something probably went wrong if char_count larger then INT_MAX.
         */
        if (char_count == 0 || char_count > INT_MAX) {
                return -1;
        }
 
        // Will always be able to write null terminator.
        int ret = vsnprintf(chars, char_count, fmt, args);
        if (ret < 0) {
                return ret;
        }
 
        // Safe, ret is checked for negative above.
        if ((size_t)ret > char_count - 1) {
                return (int)char_count - 1;
        }
 
        return ret;
}
 
/*!
 * We want to truncate the value, not get the possible written, and error when
 * we can not write out anything.
 *
 * See @ref u_truncate_vsnprintf for more info.
 *
 * @ingroup @aux_util
 */
static inline int
u_truncate_snprintf(char *chars, size_t char_count, const char *fmt, ...)
{
        /*
         * We always want to be able to write null terminator, and
         * something probably went wrong if char_count larger then INT_MAX.
         */
        if (char_count == 0 || char_count > INT_MAX) {
                return -1;
        }
 
        va_list args;
        va_start(args, fmt);
        int ret = u_truncate_vsnprintf(chars, char_count, fmt, args);
        va_end(args);
 
        return ret;
}
 
 
#ifdef __cplusplus
}
#endif