转自：https://www.cnblogs.com/Jimmy1988/p/7485133.html
1. 错误码 / errno
Linux中系统调用的错误都存储于 errno中，errno由操作系统维护，存储就近发生的错误，即下一次的错误码会覆盖掉上一次的错误。
PS: 只有当系统调用或者调用lib函数时出错，才会置位
errno！
查看系统中所有的errno所代表的含义，可以采用如下的代码：
/* Function: obtain the errno string
* char *strerror(int errno)
*/
#include <stdio.h>
#include <string.h> //for strerror()
//#include <errno.h>
int main()
{
int tmp = 0;
for(tmp = 0; tmp <=256; tmp++)
{
printf("errno: %2d\t%s\n",tmp,strerror(tmp));
}
return 0;
}输出信息如下：
errno: 0 Success
errno: 1 Operation not permitted
errno: 2 No such file or directory
errno: 3 No such process
errno: 4 Interrupted system call
errno: 5 Input/output error
errno: 6 No such device or address
errno: 7 Argument list too long
errno: 8 Exec format error
errno: 9 Bad file descriptor
errno: 10 No child processes
errno: 11 Resource temporarily unavailable
errno: 12 Cannot allocate memory
errno: 13 Permission denied
errno: 14 Bad address
errno: 15 Block device required
errno: 16 Device or resource busy
errno: 17 File exists
errno: 18 Invalid cross-device link
errno: 19 No such device
errno: 20 Not a directory
errno: 21 Is a directory
errno: 22 Invalid argument
errno: 23 Too many open files in system
errno: 24 Too many open files
errno: 25 Inappropriate ioctl for device
errno: 26 Text file busy
errno: 27 File too large
errno: 28 No space left on device
errno: 29 Illegal seek
errno: 30 Read-only file system
errno: 31 Too many links
errno: 32 Broken pipe
errno: 33 Numerical argument out of domain
errno: 34 Numerical result out of range
errno: 35 Resource deadlock avoided
errno: 36 File name too long
errno: 37 No locks available
errno: 38 Function not implemented
errno: 39 Directory not empty
errno: 40 Too many levels of symbolic links
errno: 41 Unknown error 41
errno: 42 No message of desired type
errno: 43 Identifier removed
errno: 44 Channel number out of range
errno: 45 Level 2 not synchronized
errno: 46 Level 3 halted
errno: 47 Level 3 reset
errno: 48 Link number out of range
errno: 49 Protocol driver not attached
errno: 50 No CSI structure available
errno: 51 Level 2 halted
errno: 52 Invalid exchange
errno: 53 Invalid request descriptor
errno: 54 Exchange full
errno: 55 No anode
errno: 56 Invalid request code
errno: 57 Invalid slot
errno: 58 Unknown error 58
errno: 59 Bad font file format
errno: 60 Device not a stream
errno: 61 No data available
errno: 62 Timer expired
errno: 63 Out of streams resources
errno: 64 Machine is not on the network
errno: 65 Package not installed
errno: 66 Object is remote
errno: 67 Link has been severed
errno: 68 Advertise error
errno: 69 Srmount error
errno: 70 Communication error on send
errno: 71 Protocol error
errno: 72 Multihop attempted
errno: 73 RFS specific error
errno: 74 Bad message
errno: 75 Value too large for defined data type
errno: 76 Name not unique on network
errno: 77 File descriptor in bad state
errno: 78 Remote address changed
errno: 79 Can not access a needed shared library
errno: 80 Accessing a corrupted shared library
errno: 81 .lib section in a.out corrupted
errno: 82 Attempting to link in too many shared libraries
errno: 83 Cannot exec a shared library directly
errno: 84 Invalid or incomplete multibyte or wide character
errno: 85 Interrupted system call should be restarted
errno: 86 Streams pipe error
errno: 87 Too many users
errno: 88 Socket operation on non-socket
errno: 89 Destination address