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How to print the symbolic name errno in C?

I can use perror() or strerror() to print the errno owned man-read error message, but what if I also want to print a symbolic name (like " EAGAIN ") errno ?

Any convenient feature or macro for this?

update: by adding the code that I wrote based on the idea of ​​the answer below and its comments:

 #include <ctype.h> #include <errno.h> #include <stdio.h> int get_errno_name(char *buf, int buf_size) { // Using the linux-only gawk instead of awk, because of the convenient // match() functionality. For Posix portability, use a different recipe... char cmd[] = "e= && " // errno to be inserted here (max digits = 6) "echo '#include <errno.h>' | " "gcc -dM -E - | " // optionally, use $CC inead of gcc "gawk \"match(\\$0, /^#[[:space:]]*define[[:space:]]+" "(E[[:alnum:]]+)[[:space:]]+$e($|[^[:alnum:]])/, m) " "{ print m[1] }\""; { // Insert the errno as the "e" shell variable in the command above. int errno_digit_c = snprintf(cmd + 2, 6, "%d", errno); if (errno_digit_c < 1) { fprintf(stderr, "Failed to stringify an errno " "in get_errno_name().\n"); return -1; } // Replace the inserted terminating '\0' with whitespace cmd[errno_digit_c + 2] = ' '; } FILE *f = popen(cmd, "r"); if (f == NULL) { perror("Failed to popen() in get_errno_name()"); return -1; } int read_size = 0, c; while ((c = getc(f)) != EOF) { if (isalnum(c)) { buf[read_size++] = c; if (read_size + 1 > buf_size) { fprintf(stderr, "Read errno name is larger than the character " "buffer supplied to get_errno_name().\n"); return -1; } } } buf[read_size++] = '\0'; if (pclose(f) == -1) { perror("Failed to pclose() in get_errno_name()"); return -1; } return read_size; }
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6 answers

There is no easy way to do this.

You can create a program - and I created it, which can be repackaged as a library function that converts them from a number to a name. But table generation is moderately heavy. I use a Perl script that launches the compiler (GCC or its equivalent) with parameters ( -H ) to list the headers included by /usr/include/errno.h and then scans these files looking for names ( #define plus E , followed by a letter or number in upper case), numbers and comments. It works on Linux, Mac OS X, Solaris, HP-UX, AIX. This is not particularly trivial.

Beware, errno.h on Mac OS X contains the name ELAST (the name reserved for the implementation used), which is a duplicate of the largest number (but the mapping changes from release to release, it was 105 in Mountain Lion, I believe, but it's 106 to the Mavericks).

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As far as I know, you cannot. Some integer error constants are mapped to more than one symbolic name anyway, for example. EAGAIN and EWOULDBLOCK. Obviously, you can find them on the man page of the command that installs errno.

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If you know what errors you expect, you can write large switch/case or if/else blocks against errno in the following style:

 if (errno == EAGAIN) fprintf(stderr, "EAGAIN");

The obvious problem is that if you want to specify a specific errno name, you need to write against every possible option, and there are many.

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I recently wrote an errnoname library that has an errnoname function that allows you to do this.

Unfortunately, there is still no standard API for this, and as far as I know, there is no other open source C library that would do this.

As the other answers show, the only “difficult” part is getting a list of errno names and values ​​to search for.

So in the errnoname library errnoname I see this as a separate step that you don’t have to deal with, which collects errno names for many operating systems into a list, and then generates the actually issued C code from this, so the end result is simple and efficient C, which can be compiled and run without any external dependencies from running external commands or searching for header files.

In any case, since it is released under the “Zero-Clause BSD License” (0BSD), which is an authorization license or, more precisely, a license equivalent to a public domain, you can do whatever you want with it.

Below is a direct copy and paste function from my library, so this answer can stand alone. A couple of notes:

  1. This covers all the errno names I could find for Linux, Darwin (Mac OS X and iOS X), FreeBSD, NetBSD, OpenBSD, DragonflyBSD and several closed source Unix systems starting in August 2019.

  2. It returns a NULL pointer if you give it an errno value whose name it does not know.

  3. If some system adds a new errno name, I will probably update the library, but maybe I will not forget to update this answer.

 #include <errno.h> char const * errnoname(int errno_) { switch(errno_) { #ifdef E2BIG case E2BIG: return "E2BIG"; #endif #ifdef EACCES case EACCES: return "EACCES"; #endif #ifdef EADDRINUSE case EADDRINUSE: return "EADDRINUSE"; #endif #ifdef EADDRNOTAVAIL case EADDRNOTAVAIL: return "EADDRNOTAVAIL"; #endif #ifdef EADI case EADI: return "EADI"; #endif #ifdef EADV case EADV: return "EADV"; #endif #ifdef EAFNOSUPPORT case EAFNOSUPPORT: return "EAFNOSUPPORT"; #endif #ifdef EAGAIN case EAGAIN: return "EAGAIN"; #endif #ifdef EAIO case EAIO: return "EAIO"; #endif #ifdef EALIGN case EALIGN: return "EALIGN"; #endif #ifdef EALREADY case EALREADY: return "EALREADY"; #endif #ifdef EASYNC case EASYNC: return "EASYNC"; #endif #ifdef EAUTH case EAUTH: return "EAUTH"; #endif #ifdef EBADARCH case EBADARCH: return "EBADARCH"; #endif #ifdef EBADE case EBADE: return "EBADE"; #endif #ifdef EBADEXEC case EBADEXEC: return "EBADEXEC"; #endif #ifdef EBADF case EBADF: return "EBADF"; #endif #ifdef EBADFD case EBADFD: return "EBADFD"; #endif #ifdef EBADMACHO case EBADMACHO: return "EBADMACHO"; #endif #ifdef EBADMSG case EBADMSG: return "EBADMSG"; #endif #ifdef EBADR case EBADR: return "EBADR"; #endif #ifdef EBADRPC case EBADRPC: return "EBADRPC"; #endif #ifdef EBADRQC case EBADRQC: return "EBADRQC"; #endif #ifdef EBADSLT case EBADSLT: return "EBADSLT"; #endif #ifdef EBADVER case EBADVER: return "EBADVER"; #endif #ifdef EBFONT case EBFONT: return "EBFONT"; #endif #ifdef EBUSY case EBUSY: return "EBUSY"; #endif #ifdef ECANCELED case ECANCELED: return "ECANCELED"; #endif #if defined(ECANCELLED) && (!defined(ECANCELED) || ECANCELLED != ECANCELED) case ECANCELLED: return "ECANCELLED"; #endif #ifdef ECAPMODE case ECAPMODE: return "ECAPMODE"; #endif #ifdef ECHILD case ECHILD: return "ECHILD"; #endif #ifdef ECHRNG case ECHRNG: return "ECHRNG"; #endif #ifdef ECKPT case ECKPT: return "ECKPT"; #endif #ifdef ECLONEME case ECLONEME: return "ECLONEME"; #endif #ifdef ECOMM case ECOMM: return "ECOMM"; #endif #ifdef ECONFIG case ECONFIG: return "ECONFIG"; #endif #ifdef ECONNABORTED case ECONNABORTED: return "ECONNABORTED"; #endif #ifdef ECONNREFUSED case ECONNREFUSED: return "ECONNREFUSED"; #endif #ifdef ECONNRESET case ECONNRESET: return "ECONNRESET"; #endif #ifdef ECORRUPT case ECORRUPT: return "ECORRUPT"; #endif #ifdef ECVCERORR case ECVCERORR: return "ECVCERORR"; #endif #ifdef ECVPERORR case ECVPERORR: return "ECVPERORR"; #endif #ifdef EDEADLK case EDEADLK: return "EDEADLK"; #endif #if defined(EDEADLOCK) && (!defined(EDEADLK) || EDEADLOCK != EDEADLK) case EDEADLOCK: return "EDEADLOCK"; #endif #ifdef EDESTADDREQ case EDESTADDREQ: return "EDESTADDREQ"; #endif #ifdef EDESTADDRREQ case EDESTADDRREQ: return "EDESTADDRREQ"; #endif #ifdef EDEVERR case EDEVERR: return "EDEVERR"; #endif #ifdef EDIRIOCTL case EDIRIOCTL: return "EDIRIOCTL"; #endif #ifdef EDIRTY case EDIRTY: return "EDIRTY"; #endif #ifdef EDIST case EDIST: return "EDIST"; #endif #ifdef EDOM case EDOM: return "EDOM"; #endif #ifdef EDOOFUS case EDOOFUS: return "EDOOFUS"; #endif #ifdef EDOTDOT case EDOTDOT: return "EDOTDOT"; #endif #ifdef EDQUOT case EDQUOT: return "EDQUOT"; #endif #ifdef EDUPFD case EDUPFD: return "EDUPFD"; #endif #ifdef EDUPPKG case EDUPPKG: return "EDUPPKG"; #endif #ifdef EEXIST case EEXIST: return "EEXIST"; #endif #ifdef EFAIL case EFAIL: return "EFAIL"; #endif #ifdef EFAULT case EFAULT: return "EFAULT"; #endif #ifdef EFBIG case EFBIG: return "EFBIG"; #endif #ifdef EFORMAT case EFORMAT: return "EFORMAT"; #endif #ifdef EFSCORRUPTED case EFSCORRUPTED: return "EFSCORRUPTED"; #endif #ifdef EFTYPE case EFTYPE: return "EFTYPE"; #endif #ifdef EHOSTDOWN case EHOSTDOWN: return "EHOSTDOWN"; #endif #ifdef EHOSTUNREACH case EHOSTUNREACH: return "EHOSTUNREACH"; #endif #ifdef EHWPOISON case EHWPOISON: return "EHWPOISON"; #endif #ifdef EIDRM case EIDRM: return "EIDRM"; #endif #ifdef EILSEQ case EILSEQ: return "EILSEQ"; #endif #ifdef EINIT case EINIT: return "EINIT"; #endif #ifdef EINPROG case EINPROG: return "EINPROG"; #endif #ifdef EINPROGRESS case EINPROGRESS: return "EINPROGRESS"; #endif #ifdef EINTEGRITY case EINTEGRITY: return "EINTEGRITY"; #endif #ifdef EINTR case EINTR: return "EINTR"; #endif #ifdef EINVAL case EINVAL: return "EINVAL"; #endif #ifdef EIO case EIO: return "EIO"; #endif #ifdef EIPSEC case EIPSEC: return "EIPSEC"; #endif #ifdef EISCONN case EISCONN: return "EISCONN"; #endif #ifdef EISDIR case EISDIR: return "EISDIR"; #endif #ifdef EISNAM case EISNAM: return "EISNAM"; #endif #ifdef EJUSTRETURN case EJUSTRETURN: return "EJUSTRETURN"; #endif #ifdef EKEEPLOOKING case EKEEPLOOKING: return "EKEEPLOOKING"; #endif #ifdef EKEYEXPIRED case EKEYEXPIRED: return "EKEYEXPIRED"; #endif #ifdef EKEYREJECTED case EKEYREJECTED: return "EKEYREJECTED"; #endif #ifdef EKEYREVOKED case EKEYREVOKED: return "EKEYREVOKED"; #endif #ifdef EL2HLT case EL2HLT: return "EL2HLT"; #endif #ifdef EL2NSYNC case EL2NSYNC: return "EL2NSYNC"; #endif #ifdef EL3HLT case EL3HLT: return "EL3HLT"; #endif #ifdef EL3RST case EL3RST: return "EL3RST"; #endif #ifdef ELIBACC case ELIBACC: return "ELIBACC"; #endif #ifdef ELIBBAD case ELIBBAD: return "ELIBBAD"; #endif #ifdef ELIBEXEC case ELIBEXEC: return "ELIBEXEC"; #endif #ifdef ELIBMAX case ELIBMAX: return "ELIBMAX"; #endif #ifdef ELIBSCN case ELIBSCN: return "ELIBSCN"; #endif #ifdef ELNRNG case ELNRNG: return "ELNRNG"; #endif #ifdef ELOCKUNMAPPED case ELOCKUNMAPPED: return "ELOCKUNMAPPED"; #endif #ifdef ELOOP case ELOOP: return "ELOOP"; #endif #ifdef EMEDIA case EMEDIA: return "EMEDIA"; #endif #ifdef EMEDIUMTYPE case EMEDIUMTYPE: return "EMEDIUMTYPE"; #endif #ifdef EMFILE case EMFILE: return "EMFILE"; #endif #ifdef EMLINK case EMLINK: return "EMLINK"; #endif #ifdef EMOUNTEXIT case EMOUNTEXIT: return "EMOUNTEXIT"; #endif #ifdef EMOVEFD case EMOVEFD: return "EMOVEFD"; #endif #ifdef EMSGSIZE case EMSGSIZE: return "EMSGSIZE"; #endif #ifdef EMTIMERS case EMTIMERS: return "EMTIMERS"; #endif #ifdef EMULTIHOP case EMULTIHOP: return "EMULTIHOP"; #endif #ifdef ENAMETOOLONG case ENAMETOOLONG: return "ENAMETOOLONG"; #endif #ifdef ENAVAIL case ENAVAIL: return "ENAVAIL"; #endif #ifdef ENEEDAUTH case ENEEDAUTH: return "ENEEDAUTH"; #endif #ifdef ENETDOWN case ENETDOWN: return "ENETDOWN"; #endif #ifdef ENETRESET case ENETRESET: return "ENETRESET"; #endif #ifdef ENETUNREACH case ENETUNREACH: return "ENETUNREACH"; #endif #ifdef ENFILE case ENFILE: return "ENFILE"; #endif #ifdef ENFSREMOTE case ENFSREMOTE: return "ENFSREMOTE"; #endif #ifdef ENOANO case ENOANO: return "ENOANO"; #endif #ifdef ENOATTR case ENOATTR: return "ENOATTR"; #endif #ifdef ENOBUFS case ENOBUFS: return "ENOBUFS"; #endif #ifdef ENOCONNECT case ENOCONNECT: return "ENOCONNECT"; #endif #ifdef ENOCSI case ENOCSI: return "ENOCSI"; #endif #ifdef ENODATA case ENODATA: return "ENODATA"; #endif #ifdef ENODEV case ENODEV: return "ENODEV"; #endif #ifdef ENOENT case ENOENT: return "ENOENT"; #endif #ifdef ENOEXEC case ENOEXEC: return "ENOEXEC"; #endif #ifdef ENOIOCTL case ENOIOCTL: return "ENOIOCTL"; #endif #ifdef ENOKEY case ENOKEY: return "ENOKEY"; #endif #ifdef ENOLCK case ENOLCK: return "ENOLCK"; #endif #ifdef ENOLINK case ENOLINK: return "ENOLINK"; #endif #ifdef ENOLOAD case ENOLOAD: return "ENOLOAD"; #endif #ifdef ENOMATCH case ENOMATCH: return "ENOMATCH"; #endif #ifdef ENOMEDIUM case ENOMEDIUM: return "ENOMEDIUM"; #endif #ifdef ENOMEM case ENOMEM: return "ENOMEM"; #endif #ifdef ENOMSG case ENOMSG: return "ENOMSG"; #endif #ifdef ENONET case ENONET: return "ENONET"; #endif #ifdef ENOPKG case ENOPKG: return "ENOPKG"; #endif #ifdef ENOPOLICY case ENOPOLICY: return "ENOPOLICY"; #endif #ifdef ENOPROTOOPT case ENOPROTOOPT: return "ENOPROTOOPT"; #endif #ifdef ENOREG case ENOREG: return "ENOREG"; #endif #ifdef ENOSPC case ENOSPC: return "ENOSPC"; #endif #ifdef ENOSR case ENOSR: return "ENOSR"; #endif #ifdef ENOSTR case ENOSTR: return "ENOSTR"; #endif #ifdef ENOSYM case ENOSYM: return "ENOSYM"; #endif #ifdef ENOSYS case ENOSYS: return "ENOSYS"; #endif #ifdef ENOTACTIVE case ENOTACTIVE: return "ENOTACTIVE"; #endif #ifdef ENOTBLK case ENOTBLK: return "ENOTBLK"; #endif #ifdef ENOTCAPABLE case ENOTCAPABLE: return "ENOTCAPABLE"; #endif #ifdef ENOTCONN case ENOTCONN: return "ENOTCONN"; #endif #ifdef ENOTDIR case ENOTDIR: return "ENOTDIR"; #endif #ifdef ENOTEMPTY case ENOTEMPTY: return "ENOTEMPTY"; #endif #ifdef ENOTNAM case ENOTNAM: return "ENOTNAM"; #endif #ifdef ENOTREADY case ENOTREADY: return "ENOTREADY"; #endif #ifdef ENOTRECOVERABLE case ENOTRECOVERABLE: return "ENOTRECOVERABLE"; #endif #ifdef ENOTRUST case ENOTRUST: return "ENOTRUST"; #endif #ifdef ENOTSOCK case ENOTSOCK: return "ENOTSOCK"; #endif #ifdef ENOTSUP case ENOTSUP: return "ENOTSUP"; #endif #ifdef ENOTTY case ENOTTY: return "ENOTTY"; #endif #ifdef ENOTUNIQ case ENOTUNIQ: return "ENOTUNIQ"; #endif #ifdef ENOUNLD case ENOUNLD: return "ENOUNLD"; #endif #ifdef ENOUNREG case ENOUNREG: return "ENOUNREG"; #endif #ifdef ENXIO case ENXIO: return "ENXIO"; #endif #ifdef EOPCOMPLETE case EOPCOMPLETE: return "EOPCOMPLETE"; #endif #if defined(EOPNOTSUPP) && (!defined(ENOTSUP) || EOPNOTSUPP != ENOTSUP) case EOPNOTSUPP: return "EOPNOTSUPP"; #endif #ifdef EOVERFLOW case EOVERFLOW: return "EOVERFLOW"; #endif #ifdef EOWNERDEAD case EOWNERDEAD: return "EOWNERDEAD"; #endif #ifdef EPASSTHROUGH case EPASSTHROUGH: return "EPASSTHROUGH"; #endif #ifdef EPATHREMOTE case EPATHREMOTE: return "EPATHREMOTE"; #endif #ifdef EPERM case EPERM: return "EPERM"; #endif #ifdef EPFNOSUPPORT case EPFNOSUPPORT: return "EPFNOSUPPORT"; #endif #ifdef EPIPE case EPIPE: return "EPIPE"; #endif #ifdef EPOWERF case EPOWERF: return "EPOWERF"; #endif #ifdef EPROCLIM case EPROCLIM: return "EPROCLIM"; #endif #ifdef EPROCUNAVAIL case EPROCUNAVAIL: return "EPROCUNAVAIL"; #endif #ifdef EPROGMISMATCH case EPROGMISMATCH: return "EPROGMISMATCH"; #endif #ifdef EPROGUNAVAIL case EPROGUNAVAIL: return "EPROGUNAVAIL"; #endif #ifdef EPROTO case EPROTO: return "EPROTO"; #endif #ifdef EPROTONOSUPPORT case EPROTONOSUPPORT: return "EPROTONOSUPPORT"; #endif #ifdef EPROTOTYPE case EPROTOTYPE: return "EPROTOTYPE"; #endif #ifdef EPWROFF case EPWROFF: return "EPWROFF"; #endif #ifdef EQFULL case EQFULL: return "EQFULL"; #endif #ifdef EQSUSPENDED case EQSUSPENDED: return "EQSUSPENDED"; #endif #ifdef ERANGE case ERANGE: return "ERANGE"; #endif #ifdef ERECYCLE case ERECYCLE: return "ERECYCLE"; #endif #ifdef EREDRIVEOPEN case EREDRIVEOPEN: return "EREDRIVEOPEN"; #endif #ifdef EREFUSED case EREFUSED: return "EREFUSED"; #endif #ifdef ERELOC case ERELOC: return "ERELOC"; #endif #ifdef ERELOCATED case ERELOCATED: return "ERELOCATED"; #endif #ifdef ERELOOKUP case ERELOOKUP: return "ERELOOKUP"; #endif #ifdef EREMCHG case EREMCHG: return "EREMCHG"; #endif #ifdef EREMDEV case EREMDEV: return "EREMDEV"; #endif #ifdef EREMOTE case EREMOTE: return "EREMOTE"; #endif #ifdef EREMOTEIO case EREMOTEIO: return "EREMOTEIO"; #endif #ifdef EREMOTERELEASE case EREMOTERELEASE: return "EREMOTERELEASE"; #endif #ifdef ERESTART case ERESTART: return "ERESTART"; #endif #ifdef ERFKILL case ERFKILL: return "ERFKILL"; #endif #ifdef EROFS case EROFS: return "EROFS"; #endif #ifdef ERPCMISMATCH case ERPCMISMATCH: return "ERPCMISMATCH"; #endif #ifdef ESAD case ESAD: return "ESAD"; #endif #ifdef ESHLIBVERS case ESHLIBVERS: return "ESHLIBVERS"; #endif #ifdef ESHUTDOWN case ESHUTDOWN: return "ESHUTDOWN"; #endif #ifdef ESOCKTNOSUPPORT case ESOCKTNOSUPPORT: return "ESOCKTNOSUPPORT"; #endif #ifdef ESOFT case ESOFT: return "ESOFT"; #endif #ifdef ESPIPE case ESPIPE: return "ESPIPE"; #endif #ifdef ESRCH case ESRCH: return "ESRCH"; #endif #ifdef ESRMNT case ESRMNT: return "ESRMNT"; #endif #ifdef ESTALE case ESTALE: return "ESTALE"; #endif #ifdef ESTART case ESTART: return "ESTART"; #endif #ifdef ESTRPIPE case ESTRPIPE: return "ESTRPIPE"; #endif #ifdef ESYSERROR case ESYSERROR: return "ESYSERROR"; #endif #ifdef ETIME case ETIME: return "ETIME"; #endif #ifdef ETIMEDOUT case ETIMEDOUT: return "ETIMEDOUT"; #endif #ifdef ETOOMANYREFS case ETOOMANYREFS: return "ETOOMANYREFS"; #endif #ifdef ETXTBSY case ETXTBSY: return "ETXTBSY"; #endif #ifdef EUCLEAN case EUCLEAN: return "EUCLEAN"; #endif #ifdef EUNATCH case EUNATCH: return "EUNATCH"; #endif #ifdef EUSERS case EUSERS: return "EUSERS"; #endif #ifdef EVERSION case EVERSION: return "EVERSION"; #endif #if defined(EWOULDBLOCK) && (!defined(EAGAIN) || EWOULDBLOCK != EAGAIN) case EWOULDBLOCK: return "EWOULDBLOCK"; #endif #ifdef EWRONGFS case EWRONGFS: return "EWRONGFS"; #endif #ifdef EWRPROTECT case EWRPROTECT: return "EWRPROTECT"; #endif #ifdef EXDEV case EXDEV: return "EXDEV"; #endif #ifdef EXFULL case EXFULL: return "EXFULL"; #endif } return 0; }
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I don’t know about any function that does this, but it will not be difficult to write it if you are familiar with the errors returned to your program.

You can write lines containing the outputs of strerror () and use a for loop, and if the instructions are with strcmp () (which return a value based on success or failure), compare the lines you wrote. If they are the same, you can print the symbolic name * if you set it to a different line.

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Since symbolic names are stored as enumerations, and C treats them as Ints . You will need to create a function similar to this SO query. How to convert rename names to string in c . You could probably shorten it to a macro easily enough, but creating a case for each error should be done.

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Source: https://habr.com/ru/post/957762/

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