linux系统编程之错误处理
在linux系统编程中,当系统调用出现错误时,有一个整型变量会被设置,这个整型变量就是errno,这个变量的定义在/usr/include/errno.h文件中
1 #ifndef _ERRNO_H 2 3 /* The includer defined __need_Emath if he wants only the definitions 4 of EDOM and ERANGE, and not everything else. */ 5 #ifndef __need_Emath 6 # define _ERRNO_H 1 7 # include <features.h> 8 #endif 9 10 __BEGIN_DECLS 11 12 /* Get the error number constants from the system-specific file. 13 This file will test __need_Emath and _ERRNO_H. */ 14 #include <bits/errno.h> 15 #undef __need_Emath 16 17 #ifdef _ERRNO_H 18 19 /* Declare the `errno' variable, unless it's defined as a macro by 20 bits/errno.h. This is the case in GNU, where it is a per-thread 21 variable. This redeclaration using the macro still works, but it 22 will be a function declaration without a prototype and may trigger 23 a -Wstrict-prototypes warning. */ 24 #ifndef errno 25 extern int errno; 26 #endif 27 28 #ifdef __USE_GNU 29 30 /* The full and simple forms of the name with which the program was 31 invoked. These variables are set up automatically at startup based on 32 the value of ARGV[0] (this works only if you use GNU ld). */ 33 extern char *program_invocation_name, *program_invocation_short_name; 34 #endif /* __USE_GNU */ 35 #endif /* _ERRNO_H */ 36 37 __END_DECLS 38 39 #endif /* _ERRNO_H */ 40 41 /* The Hurd <bits/errno.h> defines `error_t' as an enumerated type so 42 that printing `error_t' values in the debugger shows the names. We 43 might need this definition sometimes even if this file was included 44 before. */ 45 #if defined __USE_GNU || defined __need_error_t 46 # ifndef __error_t_defined 47 typedef int error_t; 48 # define __error_t_defined 1 49 # endif 50 # undef __need_error_t 51 #endif
当系统调用出现无错误时,这个整型变量便会被设置成一个值,每个值有一个特殊的含义,每一值用一个宏来表示,/usr/include/asm-generic/errno.h文件中定义
#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 */ #define EHWPOISON 133 /* Memory page has hardware error */ #endif
解释完了errno的含义,那么我们来用两个常用的错误输出函数
一个是perror
void perror(const char *s);//根据系统设置好的errno的值来输出错误信息 //错误信息会包含程序员自己填写的内容,以参数s传入程序员想要输出的内容
一个是strerror
char *strerror(int errnum);//把errno传入到函数strerror中,strerror返回相应错误信息的文本