perror, strerror 显示errno对应的字符串错误信息
2012-02-14 wcdj Happy Valentine's Day !
出错处理
—— 查看 errno，在定位错误信息的时候很有用
当UNIX函数出错时，常常返回一个负值，而且整形变量 errno 通常被设置为含有附加信息的一个值。（注意，不是所有情况都是）
在文件
注意：
(1) 通过 man 3 errno，查看错误常量的具体信息。
(2) The
(3) 如果调用没有出错，errno的值不会被清除，因此，仅当函数的返回值表明出错时，才应该检验其值。
(4) Valid error numbers are all non-zero; errno is never set to zero by any library function. 任一函数都不会将errno值设置为0，在
(5) errno is defined by the ISO C standard to be a modifiable lvalue of type int, and must not be explicitly declared; errno由系统定义，不可以再重新定义。
(6) errno is thread-local; setting it in one thread does not affect its value in any other thread. 在支持线程的环境中，多个线程共享进程地址空间，每个线程都有属于它自己的局部errno，以避免一个线程干扰另一个线程。
(7) It was common in traditional C to declare errno manually (i.e., extern int errno) instead of including
查看错误码具体信息的简单方法：
方法1：
find /usr/include -name "errno.h" | xargs grep 115 查看错误码信息
方法2：
man perror
perror - explain error codes
例如：
$ perror 2
OS error code 2: No such file or directory
在写程序时，C标准 定义了两个函数，用于打印出错信息：
char *strerror(int errnum); More
void perror(const char *s); More
说明
(1) #include
(2) #include
下面显示errno对应的错误信息：
#include
#include
#include
#include
#include
#include
#include
void fred(int error_number)
{
fprintf(stderr, "%3d ", error_number);
errno = error_number;
perror("test");
}/*fred()*/
int main(void)
{
int socket1;
int socket2;
int the_error;
struct timeval tv;
for(the_error = 0;
the_error <= 127;
the_error++
)
{
fred(the_error);
}
fprintf(stderr, "==== about to find EDOM\n");
fred(EDOM);
fprintf(stderr, "==== about to do socket stuff\n");
socket1 = socket(AF_INET,
SOCK_STREAM,
IPPROTO_TCP
);
if(socket1 < 0)
{
perror("first socket()");
exit(1);
}
socket2 = socket(AF_INET,
SOCK_STREAM,
IPPROTO_TCP
);
if(socket2 < 0)
{
perror("second socket()");
exit(1);
}
tv.tv_sec = 0;
//tv.tv_usec = 1000000;
tv.tv_usec = 999999;
if(setsockopt(socket1,
SOL_SOCKET,
SO_RCVTIMEO,
&tv,
sizeof(tv)
)
< 0
)
{
perror("first setsockopt()");
}
else
{
fprintf(stderr, "first setsockopt() worked\n");
}
tv.tv_sec = 1;
tv.tv_usec = 0;
if(setsockopt(socket2,
SOL_SOCKET,
SO_RCVTIMEO,
&tv,
sizeof(tv)
)
< 0
)
{
perror("second setsockopt()");
}
else
{
fprintf(stderr, "second setsockopt() worked\n");
}
return 0;
}/*main()*/
output:
0 test: Success
1 test: Operation not permitted
2 test: No such file or directory
3 test: No such process
4 test: Interrupted system call
5 test: Input/output error
6 test: No such device or address
7 test: Argument list too long
8 test: Exec format error
9 test: Bad file descriptor
10 test: No child processes
11 test: Resource temporarily unavailable
12 test: Cannot allocate memory
13 test: Permission denied
14 test: Bad address
15 test: Block device required
16 test: Device or resource busy
17 test: File exists
18 test: Invalid cross-device link
19 test: No such device
20 test: Not a directory
21 test: Is a directory
22 test: Invalid argument
23 test: Too many open files in system
24 test: Too many open files
25 test: Inappropriate ioctl for device
26 test: Text file busy
27 test: File too large
28 test: No space left on device
29 test: Illegal seek
30 test: Read-only file system
31 test: Too many links
32 test: Broken pipe
33 test: Numerical argument out of domain
34 test: Numerical result out of range
35 test: Resource deadlock avoided
36 test: File name too long
37 test: No locks available
38 test: Function not implemented
39 test: Directory not empty
40 test: Too many levels of symbolic links
41 test: Unknown error 41
42 test: No message of desired type
43 test: Identifier removed
44 test: Channel number out of range
45 test: Level 2 not synchronized
46 test: Level 3 halted
47 test: Level 3 reset
48 test: Link number out of range
49 test: Protocol driver not attached
50 test: No CSI structure available
51 test: Level 2 halted
52 test: Invalid exchange
53 test: Invalid request descriptor
54 test: Exchange full
55 test: No anode
56 test: Invalid request code
57 test: Invalid slot
58 test: Unknown error 58
59 test: Bad font file format
60 test: Device not a stream
61 test: No data available
62 test: Timer expired
63 test: Out of streams resources
64 test: Machine is not on the network
65 test: Package not installed
66 test: Object is remote
67 test: Link has been severed
68 test: Advertise error
69 test: Srmount error
70 test: Communication error on send
71 test: Protocol error
72 test: Multihop attempted
73 test: RFS specific error
74 test: Bad message
75 test: Value too large for defined data type
76 test: Name not unique on network
77 test: File descriptor in bad state
78 test: Remote address changed
79 test: Can not access a needed shared library
80 test: Accessing a corrupted shared library
81 test: .lib section in a.out corrupted
82 test: Attempting to link in too many shared libraries
83 test: Cannot exec a shared library directly
84 test: Invalid or incomplete multibyte or wide character
85 test: Interrupted system call should be restarted
86 test: Streams pipe error
87 test: Too many users
88 test: Socket operation on non-socket
89 test: Destination address required
90 test: Message too long
91 test: Protocol wrong type for socket
92 test: Protocol not available
93 test: Protocol not supported
94 test: Socket type not supported
95 test: Operation not supported
96 test: Protocol family not supported
97 test: Address family not supported by protocol
98 test: Address already in use
99 test: Cannot assign requested address
100 test: Network is down
101 test: Network is unreachable
102 test: Network dropped connection on reset
103 test: Software caused connection abort
104 test: Connection reset by peer
105 test: No buffer space available
106 test: Transport endpoint is already connected
107 test: Transport endpoint is not connected
108 test: Cannot send after transport endpoint shutdown
109 test: Too many references: cannot splice
110 test: Connection timed out
111 test: Connection refused
112 test: Host is down
113 test: No route to host
114 test: Operation already in progress
115 test: Operation now in progress
116 test: Stale NFS file handle
117 test: Structure needs cleaning
118 test: Not a XENIX named type file
119 test: No XENIX semaphores available
120 test: Is a named type file
121 test: Remote I/O error
122 test: Disk quota exceeded
123 test: No medium found
124 test: Wrong medium type
125 test: Operation canceled
126 test: Required key not available
127 test: Key has expired
==== about to find EDOM
33 test: Numerical argument out of domain
==== about to do socket stuff
first setsockopt() worked
second setsockopt() worked