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  • Linux C errno出错处理

    1. 出错处理errno

    每个进程维护一个全局整型变量errno, 记录系统(调用)的最后一次错误代码. errno及其常量值定义位于<errno.h>.
    以前, errno不是线程安全的, 其定义是:

    extern int errno;
    

    现在, 为支持多线程环境, errno定义是:

    extern int *__errno_location(void);
    #define errno (*__errno_location())
    

    errno与多线程:
    每个线程都有属于直接的局部errno(errno副本), 可以避免一个线程干扰另外一个线程.

    errno使用规则:

    1. 如果没有出错, errno值不会被例程清除. 只有函数返回值表明出错时, 才检验errno值;
    2. 任何函数都不会将errno设置为0, errno.h定义的所有常量也不为0;

    errno错误输出:
    C标准定义了2个函数, 用于打印出错信息: perror和strerror.


    2. 错误输出perror

    perror基于当前errno值, 输出除外信息到stderr. 也就是说, 只有函数出错返回时, 会设置errno时, 才能用perror输出错误信息.

    #include <stdio.h>
    
    void perror(const char *msg);
    

    如系统调用fork失败, 可以输出失败的详细信息:

    int ret = fork();
    if (ret < 0) {
        perorr("fork failed");
        exit(1);
    }
    

    3. 错误输出strerror

    strerror将errnum(通常是errno值)转化为出错消息字符串. 有些函数/系统调用, 如pthread_create, 是不会设置errnor的, 此时就可以利用strerror将函数返回错误码, 转化为出错字符串, 然后输出到stdout/stderr.
    至于函数调用失败时, 如何确认是否设置errno, 可以查看man手册.

    #include <string.h>
    
    char *strerror(int errnum);
    
    pthread_t th1;
    int ret = pthread_create(&th1, NULL, thr_func, NULL);
    if (ret < 0) {
        printf("%s
    ", strerror(ret));
        exit(1);
    }
    

    4. errno出错常量

    errno值宏定义值位于 error.h, 用命令man 3 errno查看. 不过, 这种方法只能看到宏和对应注释含义, 无法看到定义的数值.

    或者安装ctags后, 可以输入vim -t命令查看任意一个标识符, 如查看EINTR

    $ vim -t EINTR
    

    所有errno取值:

    #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  /* Argument 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 */
    
    /*
     * This error code is special: arch syscall entry code will return
     * -ENOSYS if users try to call a syscall that doesn't exist.  To keep
     * failures of syscalls that really do exist distinguishable from
     * failures due to attempts to use a nonexistent syscall, syscall
     * implementations should refrain from returning -ENOSYS.
     */
    #define ENOSYS      38  /* Invalid system call number */
    
    #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 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 */
    
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  • 原文地址:https://www.cnblogs.com/fortunely/p/14818040.html
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