This is lib/get_num.c (Listing 3-6, page 59), an example from the book, The Linux Programming Interface.

The source code file is copyright 2024, Michael Kerrisk, and is licensed under the GNU Lesser General Public License, version 3.

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Function list (Bold in this list means a function is not static)

/* get_num.c

   Functions to process numeric command-line arguments.
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <limits.h>
#include <errno.h>
#include "get_num.h"
/* Print a diagnostic message that contains a function name ('fname'),
   the value of a command-line argument ('arg'), the name of that
   command-line argument ('name'), and a diagnostic error message ('msg'). */
static void
gnFail(const char *fname, const char *msg, const char *arg, const char *name)
    fprintf(stderr, "%s error", fname);
    if (name != NULL)
        fprintf(stderr, " (in %s)", name);
    fprintf(stderr, ": %s\n", msg);
    if (arg != NULL && *arg != '\0')
        fprintf(stderr, "        offending text: %s\n", arg);

/* Convert a numeric command-line argument ('arg') into a long integer,
   returned as the function result. 'flags' is a bit mask of flags controlling
   how the conversion is done and what diagnostic checks are performed on the
   numeric result; see get_num.h for details.

   'fname' is the name of our caller, and 'name' is the name associated with
   the command-line argument 'arg'. 'fname' and 'name' are used to print a
   diagnostic message in case an error is detected when processing 'arg'. */

static long
getNum(const char *fname, const char *arg, int flags, const char *name)
    long res;
    char *endptr;
    int base;

    if (arg == NULL || *arg == '\0')
        gnFail(fname, "null or empty string", arg, name);

    base = (flags & GN_ANY_BASE) ? 0 : (flags & GN_BASE_8) ? 8 :
                        (flags & GN_BASE_16) ? 16 : 10;

    errno = 0;
    res = strtol(arg, &endptr, base);
    if (errno != 0)
        gnFail(fname, "strtol() failed", arg, name);

    if (*endptr != '\0')
        gnFail(fname, "nonnumeric characters", arg, name);

    if ((flags & GN_NONNEG) && res < 0)
        gnFail(fname, "negative value not allowed", arg, name);

    if ((flags & GN_GT_0) && res <= 0)
        gnFail(fname, "value must be > 0", arg, name);

    return res;
/* Convert a numeric command-line argument string to a long integer. See the
   comments for getNum() for a description of the arguments to this function. */

getLong(const char *arg, int flags, const char *name)
    return getNum("getLong", arg, flags, name);
/* Convert a numeric command-line argument string to an integer. See the
   comments for getNum() for a description of the arguments to this function. */

getInt(const char *arg, int flags, const char *name)
    long res;

    res = getNum("getInt", arg, flags, name);

    if (res > INT_MAX || res < INT_MIN)
        gnFail("getInt", "integer out of range", arg, name);

    return res;


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