Ubuntu下errno值
每當一個Unix函數(如socket函數）中發生錯誤時，全局變量errno將被設置成一個指示錯誤類型的正整數，如果函數不返回錯誤，errno的值就沒有定義，值爲0不表示任何錯誤.且具有以E開頭的全大寫字母名字，並且通常在/usr/include/sys/errno.h中定義，在Ubuntu中存放在/usr/include/asm-generic/errno.h,
爲了方便查找，我們先給出errno.h在Ubuntu裏面的內容
#ifndef _ASM_GENERIC_ERRNO_H
#define _ASM_GENERIC_ERRNO_H
#include <asm-generic/errno-base.h>
#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 */
#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 */
#endif
在實際操作中，怎麼在系統中實時查詢errno.h的值呢？舉一個用TCP協議獲取服務器時間的例子。注意socket函數的第一參數已經由AF_INET改爲9999.
#include "unp.h"
int main(int argc, char **argv)
{
int sockfd, n;
char recvline[MAXLINE + 1];
struct sockaddr_in servaddr;
if (argc != 2)
err_quit("usage: a.out <IPaddress>");
if ( (sockfd = socket(9999, SOCK_STREAM, 0)) < 0)
err_sys("socket error");
bzero(&servaddr, sizeof(servaddr));
servaddr.sin_family = AF_INET;
servaddr.sin_port = htons(13); /* daytime server */
if (inet_pton(AF_INET, argv[1], &servaddr.sin_addr) <= 0)
err_quit("inet_pton error for %s", argv[1]);
if (connect(sockfd, (SA *) &servaddr, sizeof(servaddr)) < 0)
err_sys("connect error");
while ( (n = read(sockfd, recvline, MAXLINE)) > 0) {
recvline[n] = 0; /* null terminate */
if (fputs(recvline, stdout) == EOF)
err_sys("fputs error");
}
if (n < 0)
err_sys("read error");
exit(0);
}運行
make daytimetcpcli
./daytimetcpcli 127.0.0.1
要找出有關這個錯誤的詳細信息，我們首先在errno.h頭文件中使用grep查找字符串Address family not supported by protocol
grep 'Address family not supported by protocol' /usr/include/asm-generic/errno.h
#define EAFNOSUPPORT 97 /* Address family not supported by protocol */這就是由socket返回的errno.h值,我們然後查看手冊頁面.
man socket大多數手冊在最下面的Errors標題給出額外的信息，不過一般都很簡潔
意思就是不支持指定的地址家族，就是說AF_INET那個地方改成了9999，不支持這個地址家族。應該改成AF_INET或者AF_INET6等等.