C语言中头文件errno.h是什么含义？包含些什么内容？

errno.h 是C语言C标准函式库里的标头档，定义了通过错误码来回报错误信息的宏。

errno本身是一个整型的全局变量，当使用errno的库函数，在执行出错时，只通过函数返回指基值返回一个表示出错的标识，如-1或NULL等，具体的出错原因李缺会被赋值到errno中。通过查询errno可以确定具体的出错原因。

在errno.h中定义了一系列常见的宏，其形式为
#define EPERM 1 /* Operation not permitted */
可以划分为
1 定义一个宏名，以E开头；
2 定义其值，为一个正整数；
3 一个注释区域，说明该错误号出现时的具体错误内容。

errno.h中的条目因不同编译器的实现而有所区别，一般在100~128条哪逗辩范围内，具体内容可以在编译器的系统标准头文件夹下查看对应文件。

查看错误代码errno是调试程序的一个重要搜差知方庆搜法。当linuc C api函数发生异常时,一般会将errno变量(需include errno.h)赋一个整数值,不同的值表示世消不同的含义,可以通过查看该值推测出错的原因。

定义了对errno()的参照，以及由系统调用设定的各种出错代号的define常数.

此定义符合XENIX标准和SYSTEM V标准。
在LINUX和Windows中世梁都可李返含以使哪笑用。

给你看看linux下的error.h
/* errno is not a global variable, because that would make using it
non-reentrant. Instead, its address is returned by the function
__errno. */

#ifndef _SYS_ERRNO_H_
#ifdef __cplusplus
extern "C" {
#endif
#define _SYS_ERRNO_H_

#include

#ifndef _REENT_ONLY
#define errno (*__errno())
extern int *__errno _PARAMS ((void));
#endif

/* Please don't use these variables directly.
Use strerror instead. */
extern __IMPORT _CONST char * _CONST _sys_errlist[];
extern __IMPORT int _sys_nerr;
#ifdef __CYGWIN__
extern __IMPORT const char * const sys_errlist[];
extern __IMPORT int sys_nerr;
#endif

#define __errno_r(ptr) ((ptr)->_errno)

#define EPERM 1 /哗拍* Not super-user */
#define ENOENT 2 /* No such file or directory */咐辩
#define ESRCH 3 /* No such process */
#define EINTR 4 /* Interrupted system call */
#define EIO 5 /* I/O error */
#define ENXIO 6 /乱简羡* No such device or address */
#define E2BIG 7 /* Arg list too long */
#define ENOEXEC 8 /* Exec format error */
#define EBADF 9 /* Bad file number */
#define ECHILD 10 /* No children */
#define EAGAIN 11 /* No more processes */
#define ENOMEM 12 /* Not enough core */
#define EACCES 13 /* Permission denied */
#define EFAULT 14 /* Bad address */
#define ENOTBLK 15 /* Block device required */
#define EBUSY 16 /* Mount device busy */
#define EEXIST 17 /* File exists */
#define EXDEV 18 /* Cross-device link */
#define ENODEV 19 /* No such device */
#define ENOTDIR 20 /* Not a directory */
#define EISDIR 21 /* Is a directory */
#define EINVAL 22 /* Invalid argument */
#define ENFILE 23 /* Too many open files in system */
#define EMFILE 24 /* Too many open files */
#define ENOTTY 25 /* Not a typewriter */
#define ETXTBSY 26 /* Text file busy */
#define EFBIG 27 /* File too large */
#define ENOSPC 28 /* No space left on device */
#define ESPIPE 29 /* Illegal seek */
#define EROFS 30 /* Read only file system */
#define EMLINK 31 /* Too many links */
#define EPIPE 32 /* Broken pipe */
#define EDOM 33 /* Math arg out of domain of func */
#define ERANGE 34 /* Math result not representable */
#define ENOMSG 35 /* No message of desired type */
#define EIDRM 36 /* Identifier removed */
#define ECHRNG 37 /* Channel number out of range */
#define EL2NSYNC 38 /* Level 2 not synchronized */
#define EL3HLT 39 /* Level 3 halted */
#define EL3RST 40 /* Level 3 reset */
#define ELNRNG 41 /* Link number out of range */
#define EUNATCH 42 /* Protocol driver not attached */
#define ENOCSI 43 /* No CSI structure available */
#define EL2HLT 44 /* Level 2 halted */
#define EDEADLK 45 /* Deadlock condition */
#define ENOLCK 46 /* No record locks available */
#define EBADE 50 /* Invalid exchange */
#define EBADR 51 /* Invalid request descriptor */
#define EXFULL 52 /* Exchange full */
#define ENOANO 53 /* No anode */
#define EBADRQC 54 /* Invalid request code */
#define EBADSLT 55 /* Invalid slot */
#define EDEADLOCK 56 /* File locking deadlock error */
#define EBFONT 57 /* Bad font file fmt */
#define ENOSTR 60 /* Device not a stream */
#define ENODATA 61 /* No data (for no delay io) */
#define ETIME 62 /* Timer expired */
#define ENOSR 63 /* Out of streams resources */
#define ENONET 64 /* Machine is not on the network */
#define ENOPKG 65 /* Package not installed */
#define EREMOTE 66 /* The object is remote */
#define ENOLINK 67 /* The link has been severed */
#define EADV 68 /* Advertise error */
#define ESRMNT 69 /* Srmount error */
#define ECOMM 70 /* Communication error on send */
#define EPROTO 71 /* Protocol error */
#define EMULTIHOP 74 /* Multihop attempted */
#define ELBIN 75 /* Inode is remote (not really error) */
#define EDOTDOT 76 /* Cross mount point (not really error) */
#define EBADMSG 77 /* Trying to read unreadable message */
#define EFTYPE 79 /* Inappropriate file type or format */
#define ENOTUNIQ 80 /* Given log. name not unique */
#define EBADFD 81 /* f.d. invalid for this operation */
#define EREMCHG 82 /* Remote address changed */
#define ELIBACC 83 /* Can't access a needed shared lib */
#define ELIBBAD 84 /* Accessing a corrupted shared lib */
#define ELIBSCN 85 /* .lib section in a.out corrupted */
#define ELIBMAX 86 /* Attempting to link in too many libs */
#define ELIBEXEC 87 /* Attempting to exec a shared library */
#define ENOSYS 88 /* Function not implemented */
#define ENMFILE 89 /* No more files */
#define ENOTEMPTY 90 /* Directory not empty */
#define ENAMETOOLONG 91 /* File or path name too long */
#define ELOOP 92 /* Too many symbolic links */
#define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */
#define EPFNOSUPPORT 96 /* Protocol family not supported */
#define ECONNRESET 104 /* Connection reset by peer */
#define ENOBUFS 105 /* No buffer space available */
#define EAFNOSUPPORT 106 /* Address family not supported by protocol family */
#define EPROTOTYPE 107 /* Protocol wrong type for socket */
#define ENOTSOCK 108 /* Socket operation on non-socket */
#define ENOPROTOOPT 109 /* Protocol not available */
#define ESHUTDOWN 110 /* Can't send after socket shutdown */
#define ECONNREFUSED 111 /* Connection refused */
#define EADDRINUSE 112 /* Address already in use */
#define ECONNABORTED 113 /* Connection aborted */
#define ENETUNREACH 114 /* Network is unreachable */
#define ENETDOWN 115 /* Network interface is not configured */
#define ETIMEDOUT 116 /* Connection timed out */
#define EHOSTDOWN 117 /* Host is down */
#define EHOSTUNREACH 118 /* Host is unreachable */
#define EINPROGRESS 119 /* Connection already in progress */
#define EALREADY 120 /* Socket already connected */
#define EDESTADDRREQ 121 /* Destination address required */
#define EMSGSIZE 122 /* Message too long */
#define EPROTONOSUPPORT 123 /* Unknown protocol */
#define ESOCKTNOSUPPORT 124 /* Socket type not supported */
#define EADDRNOTAVAIL 125 /* Address not available */
#define ENETRESET 126
#define EISCONN 127 /* Socket is already connected */
#define ENOTCONN 128 /* Socket is not connected */
#define ETOOMANYREFS 129
#define EPROCLIM 130
#define EUSERS 131
#define EDQUOT 132
#define ESTALE 133
#define ENOTSUP 134 /* Not supported */
#define ENOMEDIUM 135 /* No medium (in tape drive) */
#define ENOSHARE 136 /* No such host or network path */
#define ECASECLASH 137 /* Filename exists with different case */
#define EILSEQ 138
#define EOVERFLOW 139 /* Value too large for defined data type */

/* From cygwin32. */
#define EWOULDBLOCK EAGAIN /* Operation would block */

#define __ELASTERROR 2000 /* Users can add values starting here */

#ifdef __cplusplus
}
#endif
#endif /* _SYS_ERRNO_H */

查看错误代码errno是调试程序的一个重要方法