Linux C编程--进程介绍4--errno

当linux中的C api函数发生异常时,一般会将errno变量(需includeerrno.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

errno.h中定义的错误代码值如下：
linux2.4.20-18的内核代码中的/usr/include/asm/errno.h

#ifndef _I386_ERRNO_H#define _I386_ERRNO_H#define EPERM   1 /* Operation not permitted */#define ENOENT   2 /* No such file or directory */#define ESRCH   3 /* No such process */#define EINTR   4 /* Interrupted system call */#define EIO       5 /* I/O error */#define ENXIO   6 /* No such device or address */#define E2BIG   7 /* Arg list too long */#define ENOEXEC   8 /* Exec format error */#define EBADF   9 /* Bad file number */#define ECHILD 10 /* No child processes */#define EAGAIN 11 /* Try again */#define ENOMEM 12 /* Out of memory */#define EACCES 13 /* Permission denied */#define EFAULT 14 /* Bad address */#define ENOTBLK 15 /* Block device required */#define EBUSY 16 /* Device or resource busy */#define EEXIST 17 /* File exists */#define EXDEV 18 /* Cross-device link */#define ENODEV 19 /* No such device */#define ENOTDIR 20 /* Not a directory */#define EISDIR 21 /* Is a directory */#define EINVAL 22 /* Invalid argument */#define ENFILE 23 /* File table overflow */#define EMFILE 24 /* Too many open files */#define ENOTTY 25 /* Not a typewriter */#define ETXTBSY 26 /* Text file busy */#define EFBIG 27 /* File too large */#define ENOSPC 28 /* No space left on device */#define ESPIPE 29 /* Illegal seek */#define EROFS 30 /* Read-only file system */#define EMLINK 31 /* Too many links */#define EPIPE 32 /* Broken pipe */#define EDOM 33 /* Math argument out of domain of func */#define ERANGE 34 /* Math result not representable */#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 */#endif

补充说明：

同时也可以使用strerror（）来自己翻译

下面给出两个例子：
例一：

#include <stdio.h>#include <string.h>#include <errno.h> int main(void){int   fd;extern int errno;if((fd = open("/dev/dsp",O_WRONLY)) < 0){printf("errno=%d\n",errno); char * mesg = strerror(errno);printf("Mesg:%s\n",mesg); }exit(0);}

dsp设备忙的话将输出如下：
errno=16
Mesg:Device or resource busy

例二：

#include <string.h>#include <errno.h>  /* for strerror */#include <stdio.h>int main(int argc, char ** argv){  int i = 0;  for(i = 0; i < 256; i++)  printf("errno.%02d is: %s/n", i, strerror(i));  return 0;}