sg_pr2serr.c

/*
 * Copyright (c) 2022-2023 Douglas Gilbert.
 * All rights reserved.
 * Use of this source code is governed by a BSD-style
 * license that can be found in the BSD_LICENSE file.
 *
 * SPDX-License-Identifier: BSD-2-Clause
 */

#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
#include <stdarg.h>
#include <stdbool.h>
#include <string.h>
#include <ctype.h>

#include "sg_pr2serr.h"

FILE * sg_warnings_strm = NULL;        /* would like to default to stderr */


int
pr2serr(const char * fmt, ...)
{
    va_list args;
    int n;

    va_start(args, fmt);
    n = vfprintf(stderr, fmt, args);
    va_end(args);
    return n;
}

int
pr2ws(const char * fmt, ...)
{
    va_list args;
    int n;

    va_start(args, fmt);
    n = vfprintf(sg_warnings_strm ? sg_warnings_strm : stderr, fmt, args);
    va_end(args);
    return n;
}

/* Want safe, 'n += snprintf(b + n, blen - n, ...);' pattern that can
 * be called repeatedly. However snprintf() takes an unsigned second argument
 * (size_t) that explodes if 'blen - n' goes negative. This function instead
 * uses signed integers (second argument and return value) and is safe if the
 * second argument is negative. It returns number of chars actually
 * placed in cp excluding the trailing null char. So for cp_max_len > 0 the
 * return value is always < cp_max_len; for cp_max_len <= 1 the return value
 * is 0 and no chars are written to cp. Note this means that when
 * cp_max_len = 1, this function assumes that cp[0] is the null character
 * and does nothing (and returns 0). Linux kernel has a similar function
 * called  scnprintf().  */
int
sg_scnpr(char * cp, int cp_max_len, const char * fmt, ...)
{
    va_list args;
    int n;

#ifdef DEBUG
    if (cp_max_len < 2) {
        /* stack backtrace would be good here ... */
        pr2ws("%s: buffer would overrun, 'fmt' string: %s\n", __func__, fmt);
        return 0;
    }
#else
    if (cp_max_len < 2)
        return 0;
#endif
    va_start(args, fmt);
    n = vsnprintf(cp, cp_max_len, fmt, args);
    va_end(args);
    return (n < cp_max_len) ? n : (cp_max_len - 1);
}

/* This function is similar to sg_scnpr() but takes the "n" in that pattern
 * as an extra, third argument where it is renamed 'off'. This function will
 * start writing chars at 'fcp + off' for no more than 'fcp_len - off - 1'
 * characters. The return value is the same as sg_scnpr(). */
int
sg_scn3pr(char * fcp, int fcp_len, int off, const char * fmt, ...)
{
    va_list args;
    const int cp_max_len = fcp_len - off;
    int n;

#ifdef DEBUG
    if (cp_max_len < 2) {
        /* stack backtrace would be good here ... */
        pr2ws("%s: buffer would overrun, 'fmt' string: %s\n", __func__, fmt);
        return 0;
    }
#else
    if (cp_max_len < 2)
        return 0;
#endif
    va_start(args, fmt);
    n = vsnprintf(fcp + off, fcp_len - off, fmt, args);
    va_end(args);
#ifdef DEBUG
    if (n >= cp_max_len)        /* make noise when truncation */
        pr2ws("%s: truncated [n=%d]: %s; 'fmt' string: %s\n", __func__, n,
              fcp, fmt);
#endif
    return (n < cp_max_len) ? n : (cp_max_len - 1);
}