linux下的错误捕获errno和strerror()

经常在调用linux 系统api 的时候会出现一些错误，比方说使用open() write() creat()之类的函数有些时候会返回-1，也就是调用失败，这个时候往往需要知道失败的原因。这个时候使用errno这个全局变量就相当有用了。

1 errno和strerror()函数

1.1 errno

在程序代码中包含 #include <errno.h>，然后每次程序调用失败的时候，系统会自动用用错误代码填充errno这个全局变量，这样你只需要读errno这个全局变量就可以获得失败原因了。

1.2 strerror()函数

头文件：<string.h>
函数原型：char * strerror(int errnum);
将error编码errnum转换成错误消息，通过字符串返回。

1.3 perror()函数

头文件：<stdio.h>
函数原型：void perror(const char * msg);
将错误消息输出到错误输出（stderr），并换行。如果msg为空指针或者指向字符串为空，则向错误输出打印errno对应的错误消息；如果msg不为空，则向错误输出打印msg的内容后再打印冒号、空格和errno对应的错误消息。

2 errno含义

#define ESUC 0 /* Success */

#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 /* Arg 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 */

#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 NFS 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 */

3 在本机打印errno对应错误消息

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

int main(int argc, char * argv[])
{
for(int i = 0; i < 256; ++i)
{
fprintf(stdout, "%s\n", strerror(i));
}
return 0;
}

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 NFS 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 Unknown error 126