errno

errno

errno 是記錄系統的最後一次錯誤代碼。代碼是一個int型的值,在errno.h中定義。查看錯誤代碼errno是調試程序的一個重要方法。當linux C api函數發生異常時,一般會將errno變數(需include errno.h)賦一個整數值,不同的值表示不同的含義,可以通過查看該值推測出錯的原因。在實際編程中用這一招解決了不少原本看來莫名其妙的問題。

NAME


errno - number of last error
if (somecall() == -1) {
printf("somecall() failed\n");
if (errno == ...) { ... }
}
這樣的例子並不能得到somecall這個函數的運行所產生的錯誤代碼,因為很可能是printf這個函數產生的。
if (somecall() == -1) {
int errsv = errno;
printf("somecall() failed\n");
if (errsv == ...) { ... }
這樣才能真正得到運行somecall函數所帶來的錯誤代碼。
}
注意:只有當一個庫函數失敗時,errno才會被設置。當函數成功運行時,errno的值不會被修改。這意味著我們不能通過測試errno的值來判斷是否有錯誤存在。反之,只有當被調用的函數提示有錯誤發生時檢查errno的值才有意義。

errno的一些錯誤定義


以下主要來自2.6.32的內核代碼中的/usr/include/asm-generic/errno.h及errno-base.h,輸出錯誤原因定義歸納整理如下:
#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 ENOTBLK 15
#define EBUSY 16
#define EEXIST 17
#define EXDEV 18
#define ENODEV 19
#define ENOTDIR 20
#define EISDIR 21
#define EINVAL 22
#define ENFILE 23
#define EMFILE 24
#define ENOTTY 25
#define ETXTBSY 26
#define EFBIG 27
#define ENOSPC 28
#define ESPIPE 29
#define EROFS 30
#define EMLINK 31
#define EPIPE 32
#define EDOM 33
#define ERANGE 34
#define EDEADLK 35
#define ENAMETOOLONG 36
#define ENOLCK 37
#define ENOSYS 38
#define ENOTEMPTY 39
#define ELOOP 40
#define EWOULDBLOCK EAGAIN
#define ENOMSG 42
#define EIDRM 43
#define ECHRNG 44
#define EL2NSYNC 45
#define EL3HLT 46
#define EL3RST 47
#define ELNRNG 48
#define EUNATCH 49
#define ENOCSI 50
#define EL2HLT 51
#define EBADE 52
#define EBADR 53
#define EXFULL 54
#define ENOANO 55
#define EBADRQC 56
#define EBADSLT 57
#define EDEADLOCK EDEADLK
#define EBFONT 59
#define ENOSTR 60
#define ENODATA 61
#define ETIME 62
#define ENOSR 63
#define ENONET 64
#define ENOPKG 65
#define EREMOTE 66
#define ENOLINK 67
#define EADV 68
#define ESRMNT 69
#define ECOMM 70
#define EPROTO 71
#define EMULTIHOP 72
#define EDOTDOT 73
#define EBADMSG 74
#define EOVERFLOW 75
#define ENOTUNIQ 76
#define EBADFD 77
#define EREMCHG 78
#define ELIBACC 79
#define ELIBBAD 80
#define ELIBSCN 81
#define ELIBMAX 82
#define ELIBEXEC 83
#define EILSEQ 84
#define ERESTART 85
#define ESTRPIPE 86
#define EUSERS 87
#define ENOTSOCK 88
#define EDESTADDRREQ 89
#define EMSGSIZE 90
#define EPROTOTYPE 91
#define ENOPROTOOPT 92
#define EPROTONOSUPPORT 93
#define ESOCKTNOSUPPORT 94
#define EOPNOTSUPP 95
#define EPFNOSUPPORT 96
#define EAFNOSUPPORT 97
#define EADDRINUSE 98
#define EADDRNOTAVAIL 99
#define ENETDOWN 100
#define ENETUNREACH 101
#define ENETRESET 102
#define ECONNABORTED 103
#define ECONNRESET 104
#define ENOBUFS 105
#define EISCONN 106
#define ENOTCONN 107
#define ESHUTDOWN 108
#define ETOOMANYREFS 109
#define ETIMEDOUT 110
#define ECONNREFUSED 111
#define EHOSTDOWN 112
#define EHOSTUNREACH 113
#define EALREADY 114
#define EINPROGRESS 115
#define ESTALE 116
#define EUCLEAN 117
#define ENOTNAM 118
#define ENAVAIL 119
#define EISNAM 120
#define EREMOTEIO 121
#define EDQUOT 122
#define ENOMEDIUM 123
#define EMEDIUMTYEP 124
#define ECANCELED 125
#define ENOKEY 126
#define EKEYEXPIRED 127
#define EKEYREVOKED 128
#define EKEYREJECTED 129
#define EOWNERDEAD 130
#define ENOTRECOVERABLE 131
#define ERFKILL 132
#define EHWPOISON 133