This is threads/strerror.c (Listing 31-1, page 664), an example from the book, The Linux Programming Interface.

The source code file is copyright 2022, Michael Kerrisk, and is licensed under the GNU General Public License, version 3.

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

/* strerror.c

   An implementation of strerror() that is not thread-safe.
#define _GNU_SOURCE                 /* Get '_sys_nerr' and '_sys_errlist'
                                       declarations from <stdio.h> */
#include <stdio.h>
#include <string.h>                 /* Get declaration of strerror() */

#define MAX_ERROR_LEN 256           /* Maximum length of string
                                       returned by strerror() */

static char buf[MAX_ERROR_LEN];     /* Statically allocated return buffer */
char *
strerror(int err)
    if (err < 0 || err >= _sys_nerr || _sys_errlist[err] == NULL) {
        snprintf(buf, MAX_ERROR_LEN, "Unknown error %d", err);
    } else {
        strncpy(buf, _sys_errlist[err], MAX_ERROR_LEN - 1);
        buf[MAX_ERROR_LEN - 1] = '\0';          /* Ensure null termination */

    return buf;


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