linux下错误的捕获：errno和strerror的使用
经常在调用linux 系统api 的时候会出现一些错误，比方说使用open() write() creat()之类的函数有些时候会返回-1，也就是调用失败，这个时候往往需要知道失败的原因。这个时候使用errno这个全局变量就相当有用了。
在程序代码中包含 #include
1 #include <stdio.h> 2 #include <string.h> 3 #include <errno.h> 4 int main(void) 5 { 6 int fd; 7 extern int errno; 8 if((fd =open("/dev/dsp",O_WRONLY)) < 0) 9 { 10 printf("errno=%d\n",errno); 11 } 12 13 exit(0); 14 }
如果dsp设备忙的话errno值将是16。
errno.h中定义的错误代码值如下：
查 看错误代码errno是调试程序的一个重要方法。当linuc 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。比较 麻烦的是每次都要去linux源代码里面查找错误代码的含义，现在把它贴出来，以后需要查时就来这里看了。
以下来自linux 2.4.20-18的内核代码中的/usr/include/asm/errno.h
1 #ifndef _I386_ERRNO_H 2 #define _I386_ERRNO_H 3 #define EPERM 1 /* Operation not permitted */ 4 #define ENOENT 2 /* No such file or directory */ 5 #define ESRCH 3 /* No such process */ 6 #define EINTR 4 /* Interrupted system call */ 7 #define EIO 5 /* I/O error */ 8 #define ENXIO 6 /* No such device or address */ 9 #define E2BIG 7 /* Arg list too long */ 10 #define ENOEXEC 8 /* Exec format error */ 11 #define EBADF 9 /* Bad file number */ 12 #define ECHILD 10 /* No child processes */ 13 #define EAGAIN 11 /* Try again */ 14 #define ENOMEM 12 /* Out of memory */ 15 #define EACCES 13 /* Permission denied */ 16 #define EFAULT 14 /* Bad address */ 17 #define ENOTBLK 15 /* Block device required */ 18 #define EBUSY 16 /* Device or resource busy */ 19 #define EEXIST 17 /* File exists */ 20 #define EXDEV 18 /* Cross-device link */ 21 #define ENODEV 19 /* No such device */ 22 #define ENOTDIR 20 /* Not a directory */ 23 #define EISDIR 21 /* Is a directory */ 24 #define EINVAL 22 /* Invalid argument */ 25 #define ENFILE 23 /* File table overflow */ 26 #define EMFILE 24 /* Too many open files */ 27 #define ENOTTY 25 /* Not a typewriter */ 28 #define ETXTBSY 26 /* Text file busy */ 29 #define EFBIG 27 /* File too large */ 30 #define ENOSPC 28 /* No space left on device */ 31 #define ESPIPE 29 /* Illegal seek */ 32 #define EROFS 30 /* Read-only file system */ 33 #define EMLINK 31 /* Too many links */ 34 #define EPIPE 32 /* Broken pipe */ 35 #define EDOM 33 /* Math argument out of domain of func */ 36 #define ERANGE 34 /* Math result not representable */ 37 #define EDEADLK 35 /* Resource deadlock would occur */ 38 #define ENAMETOOLONG 36 /* File name too long */ 39 #define ENOLCK 37 /* No record locks available */ 40 #define ENOSYS 38 /* Function not implemented */ 41 #define ENOTEMPTY 39 /* Directory not empty */ 42 #define ELOOP 40 /* Too many symbolic links encountered */ 43 #define EWOULDBLOCK EAGAIN /* Operation would block */ 44 #define ENOMSG 42 /* No message of desired type */ 45 #define EIDRM 43 /* Identifier removed */ 46 #define ECHRNG 44 /* Channel number out of range */ 47 #define EL2NSYNC 45 /* Level 2 not synchronized */ 48 #define EL3HLT 46 /* Level 3 halted */ 49 #define EL3RST 47 /* Level 3 reset */ 50 #define ELNRNG 48 /* Link number out of range */ 51 #define EUNATCH 49 /* Protocol driver not attached */ 52 #define ENOCSI 50 /* No CSI structure available */ 53 #define EL2HLT 51 /* Level 2 halted */ 54 #define EBADE 52 /* Invalid exchange */ 55 #define EBADR 53 /* Invalid request descriptor */ 56 #define EXFULL 54 /* Exchange full */ 57 #define ENOANO 55 /* No anode */ 58 #define EBADRQC 56 /* Invalid request code */ 59 #define EBADSLT 57 /* Invalid slot */ 60 #define EDEADLOCK EDEADLK 61 #define EBFONT 59 /* Bad font file format */ 62 #define ENOSTR 60 /* Device not a stream */ 63 #define ENODATA 61 /* No data available */ 64 #define ETIME 62 /* Timer expired */ 65 #define ENOSR 63 /* Out of streams resources */ 66 #define ENONET 64 /* Machine is not on the network */ 67 #define ENOPKG 65 /* Package not installed */ 68 #define EREMOTE 66 /* Object is remote */ 69 #define ENOLINK 67 /* Link has been severed */ 70 #define EADV 68 /* Advertise error */ 71 #define ESRMNT 69 /* Srmount error */ 72 #define ECOMM 70 /* Communication error on send */ 73 #define EPROTO 71 /* Protocol error */ 74 #define EMULTIHOP 72 /* Multihop attempted */ 75 #define EDOTDOT 73 /* RFS specific error */ 76 #define EBADMSG 74 /* Not a data message */ 77 #define EOVERFLOW 75 /* Value too large for defined data type */ 78 #define ENOTUNIQ 76 /* Name not unique on network */ 79 #define EBADFD 77 /* File descriptor in bad state */ 80 #define EREMCHG 78 /* Remote address changed */ 81 #define ELIBACC 79 /* Can not access a needed shared library */ 82 #define ELIBBAD 80 /* Accessing a corrupted shared library */ 83 #define ELIBSCN 81 /* .lib section in a.out corrupted */ 84 #define ELIBMAX 82 /* Attempting to link in too many shared libraries */ 85 #define ELIBEXEC 83 /* Cannot exec a shared library directly */ 86 #define EILSEQ 84 /* Illegal byte sequence */ 87 #define ERESTART 85 /* Interrupted system call should be restarted */ 88 #define ESTRPIPE 86 /* Streams pipe error */ 89 #define EUSERS 87 /* Too many users */ 90 #define ENOTSOCK 88 /* Socket operation on non-socket */ 91 #define EDESTADDRREQ 89 /* Destination address required */ 92 #define EMSGSIZE 90 /* Message too long */ 93 #define EPROTOTYPE 91 /* Protocol wrong type for socket */ 94 #define ENOPROTOOPT 92 /* Protocol not available */ 95 #define EPROTONOSUPPORT 93 /* Protocol not supported */ 96 #define ESOCKTNOSUPPORT 94 /* Socket type not supported */ 97 #define EOPNOTSUPP 95 /* Operation not supported on transport endpoint */ 98 #define EPFNOSUPPORT 96 /* Protocol family not supported */ 99 #define EAFNOSUPPORT 97 /* Address family not supported by protocol */ 100 #define EADDRINUSE 98 /* Address already in use */ 101 #define EADDRNOTAVAIL 99 /* Cannot assign requested address */ 102 #define ENETDOWN 100 /* Network is down */ 103 #define ENETUNREACH 101 /* Network is unreachable */ 104 #define ENETRESET 102 /* Network dropped connection because of reset */ 105 #define ECONNABORTED 103 /* Software caused connection abort */ 106 #define ECONNRESET 104 /* Connection reset by peer */ 107 #define ENOBUFS 105 /* No buffer space available */ 108 #define EISCONN 106 /* Transport endpoint is already connected */ 109 #define ENOTCONN 107 /* Transport endpoint is not connected */ 110 #define ESHUTDOWN 108 /* Cannot send after transport endpoint shutdown */ 111 #define ETOOMANYREFS 109 /* Too many references: cannot splice */ 112 #define ETIMEDOUT 110 /* Connection timed out */ 113 #define ECONNREFUSED 111 /* Connection refused */ 114 #define EHOSTDOWN 112 /* Host is down */ 115 #define EHOSTUNREACH 113 /* No route to host */ 116 #define EALREADY 114 /* Operation already in progress */ 117 #define EINPROGRESS 115 /* Operation now in progress */ 118 #define ESTALE 116 /* Stale NFS file handle */ 119 #define EUCLEAN 117 /* Structure needs cleaning */ 120 #define ENOTNAM 118 /* Not a XENIX named type file */ 121 #define ENAVAIL 119 /* No XENIX semaphores available */ 122 #define EISNAM 120 /* Is a named type file */ 123 #define EREMOTEIO 121 /* Remote I/O error */ 124 #define EDQUOT 122 /* Quota exceeded */ 125 #define ENOMEDIUM 123 /* No medium found */ 126 #define EMEDIUMTYPE 124 /* Wrong medium type */ 127 #endif
同时也可以使用strerror（）来自己翻译
如：
1 #include <stdio.h> 2 #include <string.h> 3 #include <errno.h> 4 int main(void) 5 { 6 int fd; 7 extern int errno; 8 if((fd =open("/dev/dsp",O_WRONLY)) < 0) 9 { 10 printf("errno=%d\n",errno); 11 char * mesg = strerror(errno); 12 printf("Mesg:%s\n",mesg); 13 } 14 15 exit(0); 16 }
dsp设备忙的话将输出如下：
errno=16
Mesg:Device or resource busy