如何知道'errno'是什么意思？
当调用execl(...) ，我得到一个errno=2 。 这是什么意思？ 我怎么知道这个errno的含义？
您可以使用strerror()来获取错误编号的人类可读string。 这是由perror()打印的同一个string，但是如果要格式化标准错误输出以外的错误消息，这很有用。
例如：
#include <errno.h> #include <string.h> /* ... */ if(read(fd, buf, 1)==-1) { printf("Oh dear, something went wrong with read()! %s\n", strerror(errno)); }
Linux也支持显式线程安全变体strerror_r() 。
您可以使用以下一行代码检索系统上errno值的完整列表，而不是在您的系统上运行perror ：
cpp -dM /usr/include/errno.h | grep 'define E' | sort -n -k 3
在Linux上，还有一个非常简洁的工具，可以告诉每个错误代码的含义。 在Ubuntu上： apt-get install errno 。
然后，如果您想要获取错误types2的描述，只需在terminal中inputerrno 2 。
用errno -l你会得到一个包含所有错误和他们描述的列表。 以前的海报提到的其他方法要容易得多。
错误代码2意味着“找不到文件/目录”。 一般来说，你可以使用perror函数来打印一个可读的string。
这是errno -l的输出重新格式化以提高可读性：
1 EPERM Operation not permitted 2 ENOENT No such file or directory 3 ESRCH No such process 4 EINTR Interrupted system call 5 EIO Input/output error 6 ENXIO No such device or address 7 E2BIG Argument list too long 8 ENOEXEC Exec format error 9 EBADF Bad file descriptor 10 ECHILD No child processes 11 EAGAIN Resource temporarily unavailable 11 EWOULDBLOCK Resource temporarily unavailable 12 ENOMEM Cannot allocate memory 13 EACCES Permission denied 14 EFAULT Bad address 15 ENOTBLK Block device required 16 EBUSY Device or resource busy 17 EEXIST File exists 18 EXDEV Invalid cross-device link 19 ENODEV No such device 20 ENOTDIR Not a directory 21 EISDIR Is a directory 22 EINVAL Invalid argument 23 ENFILE Too many open files in system 24 EMFILE Too many open files 25 ENOTTY Inappropriate ioctl for device 26 ETXTBSY Text file busy 27 EFBIG File too large 28 ENOSPC No space left on device 29 ESPIPE Illegal seek 30 EROFS Read-only file system 31 EMLINK Too many links 32 EPIPE Broken pipe 33 EDOM Numerical argument out of domain 34 ERANGE Numerical result out of range 35 EDEADLK Resource deadlock avoided 35 EDEADLOCK Resource deadlock avoided 36 ENAMETOOLONG File name too long 37 ENOLCK No locks available 38 ENOSYS Function not implemented 39 ENOTEMPTY Directory not empty 40 ELOOP Too many levels of symbolic links 42 ENOMSG No message of desired type 43 EIDRM Identifier removed 44 ECHRNG Channel number out of range 45 EL2NSYNC Level 2 not synchronized 46 EL3HLT Level 3 halted 47 EL3RST Level 3 reset 48 ELNRNG Link number out of range 49 EUNATCH Protocol driver not attached 50 ENOCSI No CSI structure available 51 EL2HLT Level 2 halted 52 EBADE Invalid exchange 53 EBADR Invalid request descriptor 54 EXFULL Exchange full 55 ENOANO No anode 56 EBADRQC Invalid request code 57 EBADSLT Invalid slot 59 EBFONT Bad font file format 60 ENOSTR Device not a stream 61 ENODATA No data available 62 ETIME Timer expired 63 ENOSR Out of streams resources 64 ENONET Machine is not on the network 65 ENOPKG Package not installed 66 EREMOTE Object is remote 67 ENOLINK Link has been severed 68 EADV Advertise error 69 ESRMNT Srmount error 70 ECOMM Communication error on send 71 EPROTO Protocol error 72 EMULTIHOP Multihop attempted 73 EDOTDOT RFS specific error 74 EBADMSG Bad message 75 EOVERFLOW Value too large for defined data type 76 ENOTUNIQ Name not unique on network 77 EBADFD File descriptor in bad state 78 EREMCHG Remote address changed 79 ELIBACC Can not access a needed shared library 80 ELIBBAD Accessing a corrupted shared library 81 ELIBSCN .lib section in a.out corrupted 82 ELIBMAX Attempting to link in too many shared libraries 83 ELIBEXEC Cannot exec a shared library directly 84 EILSEQ Invalid or incomplete multibyte or wide character 85 ERESTART Interrupted system call should be restarted 86 ESTRPIPE Streams pipe error 87 EUSERS Too many users 88 ENOTSOCK Socket operation on non-socket 89 EDESTADDRREQ Destination address required 90 EMSGSIZE Message too long 91 EPROTOTYPE Protocol wrong type for socket 92 ENOPROTOOPT Protocol not available 93 EPROTONOSUPPORT Protocol not supported 94 ESOCKTNOSUPPORT Socket type not supported 95 ENOTSUP Operation not supported 95 EOPNOTSUPP Operation not supported 96 EPFNOSUPPORT Protocol family not supported 97 EAFNOSUPPORT Address family not supported by protocol 98 EADDRINUSE Address already in use 99 EADDRNOTAVAIL Cannot assign requested address 100 ENETDOWN Network is down 101 ENETUNREACH Network is unreachable 102 ENETRESET Network dropped connection on reset 103 ECONNABORTED Software caused connection abort 104 ECONNRESET Connection reset by peer 105 ENOBUFS No buffer space available 106 EISCONN Transport endpoint is already connected 107 ENOTCONN Transport endpoint is not connected 108 ESHUTDOWN Cannot send after transport endpoint shutdown 109 ETOOMANYREFS Too many references: cannot splice 110 ETIMEDOUT Connection timed out 111 ECONNREFUSED Connection refused 112 EHOSTDOWN Host is down 113 EHOSTUNREACH No route to host 114 EALREADY Operation already in progress 115 EINPROGRESS Operation now in progress 116 ESTALE Stale file handle 117 EUCLEAN Structure needs cleaning 118 ENOTNAM Not a XENIX named type file 119 ENAVAIL No XENIX semaphores available 120 EISNAM Is a named type file 121 EREMOTEIO Remote I/O error 122 EDQUOT Disk quota exceeded 123 ENOMEDIUM No medium found 124 EMEDIUMTYPE Wrong medium type 125 ECANCELED Operation canceled 126 ENOKEY Required key not available 127 EKEYEXPIRED Key has expired 128 EKEYREVOKED Key has been revoked 129 EKEYREJECTED Key was rejected by service 130 EOWNERDEAD Owner died 131 ENOTRECOVERABLE State not recoverable 132 ERFKILL Operation not possible due to RF-kill 133 EHWPOISON Memory page has hardware error
我用Vim中的tabularise来alignment列：
:%Tab /^[^ ]*\zs /r1l1l1 :%Tab /^ *[^ ]* *[^ ]*\zs /l1
处理errno有几个有用的function。 （只是为了说清楚，这些内置到libc – 我只是提供示例实现，因为有些人发现阅读代码比阅读英文更清晰。）
#include <string.h> char *strerror(int errnum); /* you can think of it as being implemented like this: */ static char strerror_buf[1024]; const char *sys_errlist[] = { [EPERM] = "Operation not permitted", [ENOENT] = "No such file or directory", [ESRCH] = "No such process", [EINTR] = "Interrupted system call", [EIO] = "I/O error", [ENXIO] = "No such device or address", [E2BIG] = "Argument list too long", /* etc. */ }; int sys_nerr = sizeof(sys_errlist) / sizeof(char *); char *strerror(int errnum) { if (0 <= errnum && errnum < sys_nerr && sys_errlist[errnum]) strcpy(strerror_buf, sys_errlist[errnum]); else sprintf(strerror_buf, "Unknown error %d", errnum); return strerror_buf; }
strerror返回一个string，描述你传递给它的错误号。 注意，这不是线程或中断安全的。 它可以自由地重写string，并在下一次调用时返回相同的指针。 如果你需要担心这个，请使用strerror_r 。
#include <stdio.h> void perror(const char *s); /* you can think of it as being implemented like this: */ void perror(const char *s) { fprintf(stderr, "%s: %s\n", s, strerror(errno)); }
perror打印出你给它的信息，加上描述当前errno的string，标准错误。
#include <errno.h> #include <stdio.h> #include <stdlib.h> int main(int i, char *c[]) { if (i != 2) fprintf(stderr, "Usage: perror errno\n"); else { errno = atoi(c[1]); perror(""); } exit(0); }
在Solaris上运行。
cc perror.c -o perror <<用这行来编译它
这里是文档 。 那应该告诉你这是什么意思，怎么处理它们。 您应该避免使用数字值，并使用在那里列出的常量，因为数字可能会在不同的系统之间改变。
这比在errno.h查找代码快，比在这里发布的大多数解决scheme更短，并且不需要安装第三方工具：
perl -E 'say $!=shift' 2
产量
No such file or directory
我使用以下脚本：
#!/usr/bin/python import errno import os import sys toname = dict((str(getattr(errno, x)), x) for x in dir(errno) if x.startswith("E")) tocode = dict((x, getattr(errno, x)) for x in dir(errno) if x.startswith("E")) for arg in sys.argv[1:]: if arg in tocode: print arg, tocode[arg], os.strerror(tocode[arg]) elif arg in toname: print toname[arg], arg, os.strerror(int(arg)) else: print "Unknown:", arg
呼叫
perror("execl");
在出错的情况下。
样品：
if(read(fd, buf, 1)==-1) { perror("read"); }
errno(3)和perror(3)也很有趣。
当你使用strace （在Linux上）运行你的二进制文件时，它会输出系统调用的返回值以及错误编号的含义。 这有时对你有用。
我在.bashrc文件中有以下function – 它从头文件中查找errno值（可以是/usr/include/linux/errno.h等等）。 ）
如果在机器上安装了头文件，它将起作用;-)
通常头文件有错误+接下来是注释中的解释; 以下几点：
./asm-generic/errno-base.h:#define EAGAIN 11 / *再试一次* /
function errno() { local arg=$1 if [[ "x$arg" == "xh" ]]; then cat <<EOF Usage: errno <num> Prints text that describes errno error number EOF else pushd /usr/include find . -name "errno*.h" | xargs grep "[[:space:]]${arg}[[:space:]]" popd fi }
它的意思是：
找不到文件或目录。
键入sudo apt-get install errno然后一旦安装，键入errno -l为所有错误号。 你也可以通过pipe道inputgrep来查看文件，如下所示： errno | grep file errno | grep file 。
