Ubuntu下errno值
每当一个Unix函数(如socket函数）中错误发生时，全局变量errno将被设置成一个指示错误类型的正整数，假设函数不返回错误，errno的值就未定义，值为0不表示不论什么错误.且具有以E开头的全大写字母名字。而且通常在/usr/include/sys/errno.h中定义，在Ubuntu中存放在/usr/include/asm-generic/errno.h,
为了方便查找，我们先给出errno.h在Ubuntu里面的内容
#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 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
在实际操作中，怎么在系统中实时查询errno.h的值呢？举一个用TCP协议获取server时间的样例。
注意socket函数的第一參数已经由AF_INET改为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 "); 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);} 执行 make daytimetcpcli./daytimetcpcli 127.0.0.1
要找出有关这个错误的具体信息，我们首先在errno.h头文件里使用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 */这就是由socket返回的errno.h值,我们然后查看手冊页面.
man socket大多数手冊在最以下的Errors标题给出额外的信息，只是一般都非常简洁
意思就是不支持指定的地址家族，就是说AF_INET那个地方改成了9999，不支持这个地址家族。应该改成AF_INET或者AF_INET6等等.