前言
当UNIX函数出现错误时，常常返回一个负值，而且整型变量errno通常被设置为含有附加信息的一个值。例如，open函数如果成功执行则返回一个非负文件描述符，如出错则返回-1.在open出错时，有大约15种不同的errno值（文件不存在、权限问题等）。某些函数并不返回负值而是使用另一种约定。例如，返回一个指向对象指针的大多数函数，在出错时，将返回一个NULL指针。
文件====中定义了符号errno以及可以赋予的各个常量，这些常量都以字符E开头。例如，若errno等于常量EACESS，这表示产生了权限问题（例如，没有打开所要求文件的足够权限）。
POSIX和ISO C将errno定义为这一一个符号，它扩展成为一个可以修改的整型左值。这可以是包含出错编号的一个整数，或是一个返回出错编号指针的函数。以前使用的定义是：
extern int errno;
但是在支持线程的环境中，多个线程共享进程地址空间，
每个线程都有属于自己的局部errno以避免一个线程干扰另一个线程。
对于errno应当知道两条规则。第一条规则：如果没有出错，则其值不会被一个例程清除。因此，仅当函数返回指明出错时，才检验其值。第二条：任何一个函数都不会将errno值设置为0，在中定义的所有常量都不为0。
C标准定义了两个函数，它们帮助打印出错信息。
#include char *strerror(int errnum);
1
2
此函数将errnum（它通常就是errno值）映射到一个出错信息字符串，并且返回此字符串的指针。
perror函数基于errno的当前值，在标准错误上产生一条出错信息，
#include void perror(const char *msg);
1
2
3
它首先输出由msg指向的字符串，然后是一个冒号，一个空格，接着是对应于errno值的出错信息，最后是一个换行符。
出错恢复
可与将中定义的各种出错分出
致命性的
和
非致命性的
两类。对于致命性的错误，无法执行恢复动作，最多只能在用户屏幕上打印一条出错信息，或者将一条出错信息写到日志文件中，然后终止。关于这点可以看我的：段错误？打的就是段错误！
而对于非致命性错误，有课可以较为妥善的处理。大多数非致命性错误在本质上是暂时的，例如资源短缺，当系统中活动较少时，这种出错很可能就不会发生。
与资源相关的非致命性出错包括EAGAIN. ENFILE、ENOBUFS、ENOLCK、ENOSPC、ENOSR、EWOULDBLOCK, 有时ENOMEM也是非致命性出错。当EBUSY指明共享资源正在使用时，也可将它作为非致命性出错处理。当EINTR中断- -慢速系统调用时，可将它作为非致命性出错处理。
对于资源相关的非致命性出错，一般恢复动作是延迟一些时间， 然后再试。这种技术可应用于其他情况。例如，假设-个 出错表明一个 网络连接不再起作用， 那么应用程序可以在短时间延迟后重建该连接。某些应用使用指数补偿算法，在每次重复中等待更长时间。
最后，取决于应用程序的开发者，他可以决定那些出错是可恢复的。如若使用一种从错误中恢复的合理策略，那么由于避免了应用程序的异常终止，就能改善应用程序的健壮性。
栗子
对于中断的read、write系 统调用，POSIX.I的语 义在该标准的2001版有所改变。对于如何处理已read、write部分数据量的相应系统调用，早期版本允许实现进行选择。如若read系统调用已接收并传送数据至应用程序缓冲区，但尚未接收到应用程序请求的全部数据，此时被中断、操作系统可以认为该系统调用失败、并将errno设置为EINTR;另一种处理方式是允许该系统调用成功返回，返回已接收到的部分数据量。与此类似，如若write巳传输了应用程序缓冲区中的部分数据，然后被中断，操作系统可以认为该系统调用失败，并将ermo设置为EINTR;另一种处理方式是允许该系统调用成功返回，返回已写的部分数据量。历史上，从系统V派生的实现，将这种系统调用视为失败，而BSD派生的实现则处理为部分成功返回。POSIX.1 标准的2001版采用BSD风格的语义。
假定一个读操作，它被中断，我们要恢复它：
again: if(n= read(fd, buf, BUFSIZE)) < 0) if (errno == EINTR) goto again;/* just an interrupted system call * / /* handle other errors */
1
2
3
4
5
6
errno表
其实看不看这个表意义不大，但是有的人他就是想看，那我就贴一份吧。
查看系统中所有的errno所代表的含义，可以采用如下的代码： /* Function: obtain the errno string * char *strerror(int errno) */ #include #include //for strerror() //#include int main() { int tmp = 0; for(tmp = 0; tmp <=256; tmp++) { printf("errno: %2d\t%s\n",tmp,strerror(tmp)); } return 0; } 输出信息如下： errno: 0 Success errno: 1 Operation not permitted errno: 2 No such file or directory errno: 3 No such process errno: 4 Interrupted system call errno: 5 Input/output error errno: 6 No such device or address errno: 7 Argument list too long errno: 8 Exec format error errno: 9 Bad file descriptor errno: 10 No child processes errno: 11 Resource temporarily unavailable errno: 12 Cannot allocate memory errno: 13 Permission denied errno: 14 Bad address errno: 15 Block device required errno: 16 Device or resource busy errno: 17 File exists errno: 18 Invalid cross-device link errno: 19 No such device errno: 20 Not a directory errno: 21 Is a directory errno: 22 Invalid argument errno: 23 Too many open files in system errno: 24 Too many open files errno: 25 Inappropriate ioctl for device errno: 26 Text file busy errno: 27 File too large errno: 28 No space left on device errno: 29 Illegal seek errno: 30 Read-only file system errno: 31 Too many links errno: 32 Broken pipe errno: 33 Numerical argument out of domain errno: 34 Numerical result out of range errno: 35 Resource deadlock avoided errno: 36 File name too long errno: 37 No locks available errno: 38 Function not implemented errno: 39 Directory not empty errno: 40 Too many levels of symbolic links errno: 41 Unknown error 41 errno: 42 No message of desired type errno: 43 Identifier removed errno: 44 Channel number out of range errno: 45 Level 2 not synchronized errno: 46 Level 3 halted errno: 47 Level 3 reset errno: 48 Link number out of range errno: 49 Protocol driver not attached errno: 50 No CSI structure available errno: 51 Level 2 halted errno: 52 Invalid exchange errno: 53 Invalid request descriptor errno: 54 Exchange full errno: 55 No anode errno: 56 Invalid request code errno: 57 Invalid slot errno: 58 Unknown error 58 errno: 59 Bad font file format errno: 60 Device not a stream errno: 61 No data available errno: 62 Timer expired errno: 63 Out of streams resources errno: 64 Machine is not on the network errno: 65 Package not installed errno: 66 Object is remote errno: 67 Link has been severed errno: 68 Advertise error errno: 69 Srmount error errno: 70 Communication error on send errno: 71 Protocol error errno: 72 Multihop attempted errno: 73 RFS specific error errno: 74 Bad message errno: 75 Value too large for defined data type errno: 76 Name not unique on network errno: 77 File descriptor in bad state errno: 78 Remote address changed errno: 79 Can not access a needed shared library errno: 80 Accessing a corrupted shared library errno: 81 .lib section in a.out corrupted errno: 82 Attempting to link in too many shared libraries errno: 83 Cannot exec a shared library directly errno: 84 Invalid or incomplete multibyte or wide character errno: 85 Interrupted system call should be restarted errno: 86 Streams pipe error errno: 87 Too many users errno: 88 Socket operation on non-socket errno: 89 Destination address required errno: 90 Message too long errno: 91 Protocol wrong type for socket errno: 92 Protocol not available errno: 93 Protocol not supported errno: 94 Socket type not supported errno: 95 Operation not supported errno: 96 Protocol family not supported errno: 97 Address family not supported by protocol errno: 98 Address already in use errno: 99 Cannot assign requested address errno: 100 Network is down errno: 101 Network is unreachable errno: 102 Network dropped connection on reset errno: 103 Software caused connection abort errno: 104 Connection reset by peer errno: 105 No buffer space available errno: 106 Transport endpoint is already connected errno: 107 Transport endpoint is not connected errno: 108 Cannot send after transport endpoint shutdown errno: 109 Too many references: cannot splice errno: 110 Connection timed out errno: 111 Connection refused errno: 112 Host is down errno: 113 No route to host errno: 114 Operation already in progress errno: 115 Operation now in progress errno: 116 Stale file handle errno: 117 Structure needs cleaning errno: 118 Not a XENIX named type file errno: 119 No XENIX semaphores available errno: 120 Is a named type file errno: 121 Remote I/O error errno: 122 Disk quota exceeded errno: 123 No medium found errno: 124 Wrong medium type errno: 125 Operation canceled errno: 126 Required key not available errno: 127 Key has expired errno: 128 Key has been revoked errno: 129 Key was rejected by service errno: 130 Owner died errno: 131 State not recoverable errno: 132 Operation not possible due to RF-kill errno: 133 Memory page has hardware error errno: 134~255 unknown error! Linux中，在头文件 /usr/include/asm-generic/errno-base.h 对基础常用errno进行了宏定义： #ifndef _ASM_GENERIC_ERRNO_BASE_H #define _ASM_GENERIC_ERRNO_BASE_H #define EPERM 1 /* Operation not permitted */ #define ENOENT 2 /* No such file or directory */ #define ESRCH 3 /* No such process */ #define EINTR 4 /* Interrupted system call */ #define EIO 5 /* I/O error */ #define ENXIO 6 /* No such device or address */ #define E2BIG 7 /* Argument list too long */ #define ENOEXEC 8 /* Exec format error */ #define EBADF 9 /* Bad file number */ #define ECHILD 10 /* No child processes */ #define EAGAIN 11 /* Try again */ #define ENOMEM 12 /* Out of memory */ #define EACCES 13 /* Permission denied */ #define EFAULT 14 /* Bad address */ #define ENOTBLK 15 /* Block device required */ #define EBUSY 16 /* Device or resource 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 /* File table overflow */ #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 argument out of domain of func */ #define ERANGE 34 /* Math result not representable */ #endif 在 /usr/include/asm-asm-generic/errno.h 中，对剩余的errno做了宏定义： #ifndef _ASM_GENERIC_ERRNO_H #define _ASM_GENERIC_ERRNO_H #include #define EDEADLK 35 /* Resource deadlock would occur */ #define ENAMETOOLONG 36 /* File name too long */ #define ENOLCK 37 /* No record locks available */ #define ENOSYS 38 /* Function not implemented */ #define ENOTEMPTY 39 /* Directory not empty */ #define ELOOP 40 /* Too many symbolic links encountered */ #define EWOULDBLOCK EAGAIN /* Operation would block */ #define ENOMSG 42 /* No message of desired type */ #define EIDRM 43 /* Identifier removed */ #define ECHRNG 44 /* Channel number out of range */ #define EL2NSYNC 45 /* Level 2 not synchronized */ #define EL3HLT 46 /* Level 3 halted */ #define EL3RST 47 /* Level 3 reset */ #define ELNRNG 48 /* Link number out of range */ #define EUNATCH 49 /* Protocol driver not attached */ #define ENOCSI 50 /* No CSI structure available */ #define EL2HLT 51 /* Level 2 halted */ #define EBADE 52 /* Invalid exchange */ #define EBADR 53 /* Invalid request descriptor */ #define EXFULL 54 /* Exchange full */ #define ENOANO 55 /* No anode */ #define EBADRQC 56 /* Invalid request code */ #define EBADSLT 57 /* Invalid slot */ #define EDEADLOCK EDEADLK #define EBFONT 59 /* Bad font file format */ #define ENOSTR 60 /* Device not a stream */ #define ENODATA 61 /* No data available */ #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 /* Object is remote */ #define ENOLINK 67 /* 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 72 /* Multihop attempted */ #define EDOTDOT 73 /* RFS specific error */ #define EBADMSG 74 /* Not a data message */ #define EOVERFLOW 75 /* Value too large for defined data type */ #define ENOTUNIQ 76 /* Name not unique on network */ #define EBADFD 77 /* File descriptor in bad state */ #define EREMCHG 78 /* Remote address changed */ #define ELIBACC 79 /* Can not access a needed shared library */ #define ELIBBAD 80 /* Accessing a corrupted shared library */ #define ELIBSCN 81 /* .lib section in a.out corrupted */ #define ELIBMAX 82 /* Attempting to link in too many shared libraries */ #define ELIBEXEC 83 /* Cannot exec a shared library directly */ #define EILSEQ 84 /* Illegal byte sequence */ #define ERESTART 85 /* Interrupted system call should be restarted */ #define ESTRPIPE 86 /* Streams pipe error */ #define EUSERS 87 /* Too many users */ #define ENOTSOCK 88 /* Socket operation on non-socket */ #define EDESTADDRREQ 89 /* Destination address required */ #define EMSGSIZE 90 /* Message too long */ #define EPROTOTYPE 91 /* Protocol wrong type for socket */ #define ENOPROTOOPT 92 /* Protocol not available */ #define EPROTONOSUPPORT 93 /* Protocol not supported */ #define ESOCKTNOSUPPORT 94 /* Socket type not supported */ #define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */ #define EPFNOSUPPORT 96 /* Protocol family not supported */ #define EAFNOSUPPORT 97 /* Address family not supported by protocol */ #define EADDRINUSE 98 /* Address already in use */ #define EADDRNOTAVAIL 99 /* Cannot assign requested address */ #define ENETDOWN 100 /* Network is down */ #define ENETUNREACH 101 /* Network is unreachable */ #define ENETRESET 102 /* Network dropped connection because of reset */ #define ECONNABORTED 103 /* Software caused connection abort */ #define ECONNRESET 104 /* Connection reset by peer */ #define ENOBUFS 105 /* No buffer space available */ #define EISCONN 106 /* Transport endpoint is already connected */ #define ENOTCONN 107 /* Transport endpoint is not connected */ #define ESHUTDOWN 108 /* Cannot send after transport endpoint shutdown */ #define ETOOMANYREFS 109 /* Too many references: cannot splice */ #define ETIMEDOUT 110 /* Connection timed out */ #define ECONNREFUSED 111 /* Connection refused */ #define EHOSTDOWN 112 /* Host is down */ #define EHOSTUNREACH 113 /* No route to host */ #define EALREADY 114 /* Operation already in progress */ #define EINPROGRESS 115 /* Operation now in progress */ #define ESTALE 116 /* Stale file handle */ #define EUCLEAN 117 /* Structure needs cleaning */ #define ENOTNAM 118 /* Not a XENIX named type file */ #define ENAVAIL 119 /* No XENIX semaphores available */ #define EISNAM 120 /* Is a named type file */ #define EREMOTEIO 121 /* Remote I/O error */ #define EDQUOT 122 /* Quota exceeded */ #define ENOMEDIUM 123 /* No medium found */ #define EMEDIUMTYPE 124 /* Wrong medium type */ #define ECANCELED 125 /* Operation Canceled */ #define ENOKEY 126 /* Required key not available */ #define EKEYEXPIRED 127 /* Key has expired */ #define EKEYREVOKED 128 /* Key has been revoked */ #define EKEYREJECTED 129 /* Key was rejected by service */ /* for robust mutexes */ #define EOWNERDEAD 130 /* Owner died */ #define ENOTRECOVERABLE 131 /* State not recoverable */ #define ERFKILL 132 /* Operation not possible due to RF-kill */ #define EHWPOISON 133 /* Memory page has hardware error */ #endif
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
任务调度
版权声明：本文内容由网络用户投稿，版权归原作者所有，本站不拥有其著作权，亦不承担相应法律责任。如果您发现本站中有涉嫌抄袭或描述失实的内容，请联系我们jiasou666@gmail.com 处理，核实后本网站将在24小时内删除侵权内容。
