/* SPDX-License-Identifier: GPL-3.0
 * The Language Trail
 *
 * errno.c
 *
 * https://en.cppreference.com/w/c/header/errno.html
 *
 * COPYRIGHT NOTICE
 * Copyright (C) 2025-2026 0x4248 and contributors
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the license is not changed.
 *
 * This software is free and open source. Licensed under the GNU general
 * public license version 3.0 as published by the Free Software Foundation.
*/

// Here is a rundown of some error codes:
// Note: this can differ from compiler, compiler version and system
// 0	Success
// 1	Operation not permitted
// 2	No such file or directory
// 3	No such process
// 4	Interrupted system call
// 5	Input/output error
// 6	No such device or address
// 7	Argument list too long
// 8	Exec format error
// 9	Bad file descriptor
// 10	No child processes
// 11	Resource temporarily unavailable
// 12	Cannot allocate memory
// 13	Permission denied
// 14	Bad address
// 15	Block device required
// 16	Device or resource busy
// 17	File exists
// 18	Invalid cross-device link
// 19	No such device
// 20	Not a directory
// 21	Is a directory
// 22	Invalid argument
// 23	Too many open files in system
// 24	Too many open files
// 25	Inappropriate ioctl for device
// 26	Text file busy
// 27	File too large
// 28	No space left on device
// 29	Illegal seek
// 30	Read-only file system
// 31	Too many links
// 32	Broken pipe
// 33	Numerical argument out of domain
// 34	Numerical result out of range
// 35	Resource deadlock avoided
// 36	File name too long
// 37	No locks available
// 38	Function not implemented
// 39	Directory not empty
// 40	Too many levels of symbolic links
// 41	Unknown error 41
// 42	No message of desired type
// 43	Identifier removed
// 44	Channel number out of range
// 45	Level 2 not synchronized
// 46	Level 3 halted
// 47	Level 3 reset
// 48	Link number out of range
// 49	Protocol driver not attached
// 50	No CSI structure available
// 51	Level 2 halted
// 52	Invalid exchange
// 53	Invalid request descriptor
// 54	Exchange full
// 55	No anode
// 56	Invalid request code
// 57	Invalid slot
// 58	Unknown error 58
// 59	Bad font file format
// 60	Device not a stream
// 61	No data available
// 62	Timer expired
// 63	Out of streams resources
// 64	Machine is not on the network
// 65	Package not installed
// 66	Object is remote
// 67	Link has been severed
// 68	Advertise error
// 69	Srmount error
// 70	Communication error on send
// 71	Protocol error
// 72	Multihop attempted
// 73	RFS specific error
// 74	Bad message
// 75	Value too large for defined data type
// 76	Name not unique on network
// 77	File descriptor in bad state
// 78	Remote address changed
// 79	Can not access a needed shared library
// 80	Accessing a corrupted shared library
// 81	.lib section in a.out corrupted
// 82	Attempting to link in too many shared libraries
// 83	Cannot exec a shared library directly
// 84	Invalid or incomplete multibyte or wide character
// 85	Interrupted system call should be restarted
// 86	Streams pipe error
// 87	Too many users
// 88	Socket operation on non-socket
// 89	Destination address required
// 90	Message too long
// 91	Protocol wrong type for socket
// 92	Protocol not available
// 93	Protocol not supported
// 94	Socket type not supported
// 95	Operation not supported
// 96	Protocol family not supported
// 97	Address family not supported by protocol
// 98	Address already in use
// 99	Cannot assign requested address
// 100	Network is down
// 101	Network is unreachable
// 102	Network dropped connection on reset
// 103	Software caused connection abort
// 104	Connection reset by peer
// 105	No buffer space available
// 106	Transport endpoint is already connected
// 107	Transport endpoint is not connected
// 108	Cannot send after transport endpoint shutdown
// 109	Too many references: cannot splice
// 110	Connection timed out
// 111	Connection refused
// 112	Host is down
// 113	No route to host
// 114	Operation already in progress
// 115	Operation now in progress
// 116	Stale file handle
// 117	Structure needs cleaning
// 118	Not a XENIX named type file
// 119	No XENIX semaphores available
// 120	Is a named type file
// 121	Remote I/O error
// 122	Disk quota exceeded
// 123	No medium found
// 124	Wrong medium type
// 125	Operation canceled
// 126	Required key not available
// 127	Key has expired
// 128	Key has been revoked
// 129	Key was rejected by service
// 130	Owner died
// 131	State not recoverable
// 132	Operation not possible due to RF-kill
// 133	Memory page has hardware error

/**
 * Errno maps these values to constants which can make it much easier to write
 */

#include <stdio.h>
#include <errno.h>
#include <string.h>

int foo_1(){
    return -1;
}

void foo_2(){
    /* Rather than returning an error code we can just set errno to the error */
    errno = ENOENT;
}

void test_notUsingErrno(){
    int ret;
    ret = foo_1();
    if(ret){
        printf("ERROR\n");
    } else {
        printf("OK\n");
    }
    return;
}


void test_usingErrno(){
    foo_2();
    /* We can read errno and then use strerror to tell the user what
     * went wrong
    */
    if(errno){
        /* ERROR: 2, No such file or directory */
        printf("ERROR: %d, %s\n",errno, strerror(errno));
    } else {
        printf("OK\n");
    }
    return;
}

void test_stderr(){
    /* In this demo we can het the name of an error number using stderr()
     */
    for (int i=0 ; i < 150; i++) {
        printf("%d\t%s\n", i,strerror(i));
    }
}

int main() {
    test_notUsingErrno();
    test_usingErrno();

    return 0;
}