当linux中的C api函数发生异常时,一般会将errno变量(需include
errno.h)赋一个整数值,不同的值表示不同的含义,可以通过查看该值推测出错的原因，在实际编程中用这一招解决了不少原本看来莫名其妙的问题。但是errno是一个数字，代表的具体含义还要到errno.h中去阅读宏定义，而每次查阅是一件很繁琐的事情。有下面几种方法可以方便的得到错误信息
(1)void perror(const char *s)
函数说明
perror ( )用来将上一个函数发生错误的原因输出到标准错误(stderr),参数s
所指的字符串会先打印出,后面再加上错误原因 字符串。此错误原因依照全局变量
errno 的值来决定要输出的字符串。
(2) char *strerror(int errno)
将错误代码转换为字符串错误信息,可以将该字符串和其它的信息组合输出到用户界面例如
fprintf(stderr,"error in CreateProcess %s, Process ID %d
",strerror(errno),processID)
注：假设processID是一个已经获取了的整形ID
(3)printf("%m", errno);
另外不是所有的地方发生错误的时候都可以通过error获取错误代码，例如下面的代码段
#include"stdio.h"
#include "stdlib.h"
#include "errno.h"
#include "netdb.h"
#include "sys/types.h"
#include "netinet/in.h"
int main (int argc, char *argv[])
{
struct hostent *h;
if (argc != 2)
{
fprintf (stderr ,"usage: getip address\n");
exit(1);
}
if((h=gethostbyname(argv[1])) == NULL)
{
herror("gethostbyname");
exit(1);
}
printf("Host name : %s\n", h->h_name);
printf("IP Address : %s\n", inet_ntoa (*((struct in_addr *)h->h_addr))）;
return 0;
}
通过上面的代码可以看到：使用gethostbyname()函数，你不能使用perror()来输出错误信息（因为错误代码存储在
h_errno 中而不是errno 中。所以，你需要调用herror()函数。
你简单的传给gethostbyname()
一个机器名（"bbs.tsinghua.edu.cn"），然后就从返回的结构struct hostent
中得到了IP 等其他信息．程序中输出IP 地址的程序需要解释一下：h->h_addr
是一个char*，但是inet_ntoa()函数需要传递的是一个struct in_addr
结构。所以上面将h->h_addr 强制转换为struct
in_addr*，然后通过它得到了所有数据。
linux 的errno定义，头文件#include
124 EMEDIUMTYPE Wrong medium type
123 ENOMEDIUM No medium found
122 EDQUOT Disk quota exceeded
121 EREMOTEIO Remote I/O error
120 EISNAM Is a named type file
119 ENAVAIL No XENIX semaphores available
118 ENOTNAM Not a XENIX named type file
117 EUCLEAN Structure needs cleaning
116 ESTALE Stale NFS file handle
115 EINPROGRESS +Operation now in progress
114 EALREADY Operation already in progress
113 EHOSTUNREACH No route to host
112 EHOSTDOWN Host is down
111 ECONNREFUSED Connection refused
110 ETIMEDOUT +Connection timed out
109 ETOOMANYREFS Too many references: cannot splice
108 ESHUTDOWN Cannot send after transport endpoint shutdown
107 ENOTCONN Transport endpoint is not connected
106 EISCONN Transport endpoint is already connected
105 ENOBUFS No buffer space available
104 ECONNRESET Connection reset by peer
103 ECONNABORTED Software caused connection abort
102 ENETRESET Network dropped connection on reset
101 ENETUNREACH Network is unreachable
100 ENETDOWN Network is down
99 EADDRNOTAVAIL Cannot assign requested address
98 EADDRINUSE Address already in use
97 EAFNOSUPPORT Address family not supported by protocol
96 EPFNOSUPPORT Protocol family not supported
95 EOPNOTSUPP Operation not supported
94 ESOCKTNOSUPPORT Socket type not supported
93 EPROTONOSUPPORT Protocol not supported
92 ENOPROTOOPT Protocol not available
91 EPROTOTYPE Protocol wrong type for socket
90 EMSGSIZE +Message too long
89 EDESTADDRREQ Destination address required
88 ENOTSOCK Socket operation on non-socket
87 EUSERS Too many users
86 ESTRPIPE Streams pipe error
85 ERESTART Interrupted system call should be restarted
84 EILSEQ Invalid or incomplete multibyte or wide character
83 ELIBEXEC Cannot exec a shared library directly
82 ELIBMAX Attempting to link in too many shared libraries
81 ELIBSCN .lib section in a.out corrupted
80 ELIBBAD Accessing a corrupted shared library
79 ELIBACC Can not access a needed shared library
78 EREMCHG Remote address changed
77 EBADFD File descriptor in bad state
76 ENOTUNIQ Name not unique on network
75 EOVERFLOW Value too large for defined data type
74 EBADMSG +Bad message
73 EDOTDOT RFS specific error
72 EMULTIHOP Multihop attempted
71 EPROTO Protocol error
70 ECOMM Communication error on send
69 ESRMNT Srmount error
68 EADV Advertise error
67 ENOLINK Link has been severed
66 EREMOTE Object is remote
65 ENOPKG Package not installed
64 ENONET Machine is not on the network
63 ENOSR Out of streams resources
62 ETIME Timer expired
61 ENODATA No data available
60 ENOSTR Device not a stream
59 EBFONT Bad font file format
57 EBADSLT Invalid slot
56 EBADRQC Invalid request code
55 ENOANO No anode
54 EXFULL Exchange full
53 EBADR Invalid request descriptor
52 EBADE Invalid exchange
51 EL2HLT Level 2 halted
50 ENOCSI No CSI structure available
49 EUNATCH Protocol driver not attached
48 ELNRNG Link number out of range
47 EL3RST Level 3 reset
46 EL3HLT Level 3 halted
45 EL2NSYNC Level 2 not synchronized
44 ECHRNG Channel number out of range
43 EIDRM Identifier removed
42 ENOMSG No message of desired type
40 ELOOP Too many levels of symbolic links
39 ENOTEMPTY +Directory not empty
38 ENOSYS +Function not implemented
37 ENOLCK +No locks available
36 ENAMETOOLONG +File name too long
35 EDEADLK +Resource deadlock avoided
34 ERANGE +Numerical result out of range
33 EDOM +Numerical argument out of domain
32 EPIPE +Broken pipe
31 EMLINK +Too many links
30 EROFS +Read-only file system
29 ESPIPE +Illegal seek
28 ENOSPC +No space left on device
27 EFBIG +File too large
26 ETXTBSY Text file busy
25 ENOTTY +Inappropriate ioctl for device
24 EMFILE +Too many open files
23 ENFILE +Too many open files in system
22 EINVAL +Invalid argument
21 EISDIR +Is a directory
20 ENOTDIR +Not a directory
19 ENODEV +No such device
18 EXDEV +Invalid cross-device link
17 EEXIST +File exists
16 EBUSY +Device or resource busy
15 ENOTBLK Block device required
14 EFAULT +Bad address
13 EACCES +Permission denied
12 ENOMEM +Cannot allocate memory
11 EAGAIN +Resource temporarily unavailable
10 ECHILD +No child processes
9 EBADF +Bad file descriptor
8 ENOEXEC +Exec format error
7 E2BIG +Argument list too long
6 ENXIO +No such device or address
5 EIO +Input/output error
4 EINTR +Interrupted system call
3 ESRCH +No such process
2 ENOENT +No such file or directory
1 EPERM +Operation not permitted
0 Success
