errno头文件

以前做IO操作时，常常会得到一个errno_t，其实就是整数 typedef int errno_t;

以下是VC的errno头文件，可以看出Error Code定义为一些整数值

/***
*errno.h - system wide error numbers (set by system calls)
*
*       Copyright (c) Microsoft Corporation. All rights reserved.
*
*Purpose:
*       This file defines the system-wide error numbers (set by
*       system calls).  Conforms to the XENIX standard.  Extended
*       for compatibility with Uniforum standard.
*       [System V]
*
*       [Public]
*
****/

#pragma once

#ifndef _INC_ERRNO
#define _INC_ERRNO

#include 

#ifdef __cplusplus
extern "C" {
#endif  /* __cplusplus */

/* Declare reference to errno */

#ifndef _CRT_ERRNO_DEFINED
#define _CRT_ERRNO_DEFINED
_CRTIMP extern int * __cdecl _errno(void);
#define errno   (*_errno())

errno_t __cdecl _set_errno(_In_ int _Value);
errno_t __cdecl _get_errno(_Out_ int * _Value);
#endif  /* _CRT_ERRNO_DEFINED */

/* Error Codes */

#define EPERM           1
#define ENOENT          2
#define ESRCH           3
#define EINTR           4
#define EIO             5
#define ENXIO           6
#define E2BIG           7
#define ENOEXEC         8
#define EBADF           9
#define ECHILD          10
#define EAGAIN          11
#define ENOMEM          12
#define EACCES          13
#define EFAULT          14
#define EBUSY           16
#define EEXIST          17
#define EXDEV           18
#define ENODEV          19
#define ENOTDIR         20
#define EISDIR          21
#define ENFILE          23
#define EMFILE          24
#define ENOTTY          25
#define EFBIG           27
#define ENOSPC          28
#define ESPIPE          29
#define EROFS           30
#define EMLINK          31
#define EPIPE           32
#define EDOM            33
#define EDEADLK         36
#define ENAMETOOLONG    38
#define ENOLCK          39
#define ENOSYS          40
#define ENOTEMPTY       41

/* Error codes used in the Secure CRT functions */

#ifndef RC_INVOKED
#if !defined (_SECURECRT_ERRCODE_VALUES_DEFINED)
#define _SECURECRT_ERRCODE_VALUES_DEFINED
#define EINVAL          22
#define ERANGE          34
#define EILSEQ          42
#define STRUNCATE       80
#endif  /* !defined (_SECURECRT_ERRCODE_VALUES_DEFINED) */
#endif  /* RC_INVOKED */

/* Support EDEADLOCK for compatibility with older MS-C versions */
#define EDEADLOCK       EDEADLK

/* POSIX SUPPLEMENT */
#define EADDRINUSE      100
#define EADDRNOTAVAIL   101
#define EAFNOSUPPORT    102
#define EALREADY        103
#define EBADMSG         104
#define ECANCELED       105
#define ECONNABORTED    106
#define ECONNREFUSED    107
#define ECONNRESET      108
#define EDESTADDRREQ    109
#define EHOSTUNREACH    110
#define EIDRM           111
#define EINPROGRESS     112
#define EISCONN         113
#define ELOOP           114
#define EMSGSIZE        115
#define ENETDOWN        116
#define ENETRESET       117
#define ENETUNREACH     118
#define ENOBUFS         119
#define ENODATA         120
#define ENOLINK         121
#define ENOMSG          122
#define ENOPROTOOPT     123
#define ENOSR           124
#define ENOSTR          125
#define ENOTCONN        126
#define ENOTRECOVERABLE 127
#define ENOTSOCK        128
#define ENOTSUP         129
#define EOPNOTSUPP      130
#define EOTHER          131
#define EOVERFLOW       132
#define EOWNERDEAD      133
#define EPROTO          134
#define EPROTONOSUPPORT 135
#define EPROTOTYPE      136
#define ETIME           137
#define ETIMEDOUT       138
#define ETXTBSY         139
#define EWOULDBLOCK     140

#ifdef __cplusplus
}
#endif  /* __cplusplus */

#endif  /* _INC_ERRNO */

贴在这方便以后查看

但每次对表岂不麻烦，还好好在string.h中已经定义好了通过错误码得到说明的函数 strerror

试试

#include 
#include 

int main(int argc, char* argv[])
{
    
    for (int i = 1; i < 141; i++)
    {
        char* msg = strerror(i);
        printf("%d : %s\n", i, msg);
    }
    
    getchar();
    
	return 0;
}

发现42号之后全是 Unknown error，原因是 errno 中定义之后的是兼容 Older version C的，或者是别的什么，还不清楚。？