5.27 strerror, strerror_l—convert error number to string

Synopsis

#include <string.h>
char *strerror(int errnum);
char *strerror_l(int errnum, locale_t locale);
char *_strerror_r(struct _reent ptr, int errnum,
    int internal, int *error);

Description
strerror converts the error number errnum into a string. The value of errnum is usually a copy of errno. If errnum is not a known error number, the result points to an empty string.

strerror_l is like strerror but creates a string in a format as expected in locale locale. If locale is LC_GLOBAL_LOCALE or not a valid locale object, the behaviour is undefined.

This implementation of strerror prints out the following strings for each of the values defined in ‘errno.h’:

0

Success

E2BIG

Arg list too long

EACCES

Permission denied

EADDRINUSE

Address already in use

EADDRNOTAVAIL

Address not available

EADV

Advertise error

EAFNOSUPPORT

Address family not supported by protocol family

EAGAIN

No more processes

EALREADY

Socket already connected

EBADF

Bad file number

EBADMSG

Bad message

EBUSY

Device or resource busy

ECANCELED

Operation canceled

ECHILD

No children

ECOMM

Communication error

ECONNABORTED

Software caused connection abort

ECONNREFUSED

Connection refused

ECONNRESET

Connection reset by peer

EDEADLK

Deadlock

EDESTADDRREQ

Destination address required

EEXIST

File exists

EDOM

Mathematics argument out of domain of function

EFAULT

Bad address

EFBIG

File too large

EHOSTDOWN

Host is down

EHOSTUNREACH

Host is unreachable

EIDRM

Identifier removed

EILSEQ

Illegal byte sequence

EINPROGRESS

Connection already in progress

EINTR

Interrupted system call

EINVAL

Invalid argument

EIO

I/O error

EISCONN

Socket is already connected

EISDIR

Is a directory

ELIBACC

Cannot access a needed shared library

ELIBBAD

Accessing a corrupted shared library

ELIBEXEC

Cannot exec a shared library directly

ELIBMAX

Attempting to link in more shared libraries than system limit

ELIBSCN

.lib section in a.out corrupted

EMFILE

File descriptor value too large

EMLINK

Too many links

EMSGSIZE

Message too long

EMULTIHOP

Multihop attempted

ENAMETOOLONG

File or path name too long

ENETDOWN

Network interface is not configured

ENETRESET

Connection aborted by network

ENETUNREACH

Network is unreachable

ENFILE

Too many open files in system

ENOBUFS

No buffer space available

ENODATA

No data

ENODEV

No such device

ENOENT

No such file or directory

ENOEXEC

Exec format error

ENOLCK

No lock

ENOLINK

Virtual circuit is gone

ENOMEM

Not enough space

ENOMSG

No message of desired type

ENONET

Machine is not on the network

ENOPKG

No package

ENOPROTOOPT

Protocol not available

ENOSPC

No space left on device

ENOSR

No stream resources

ENOSTR

Not a stream

ENOSYS

Function not implemented

ENOTBLK

Block device required

ENOTCONN

Socket is not connected

ENOTDIR

Not a directory

ENOTEMPTY

Directory not empty

ENOTRECOVERABLE

State not recoverable

ENOTSOCK

Socket operation on non-socket

ENOTSUP

Not supported

ENOTTY

Not a character device

ENXIO

No such device or address

EOPNOTSUPP

Operation not supported on socket

EOVERFLOW

Value too large for defined data type

EOWNERDEAD

Previous owner died

EPERM

Not owner

EPIPE

Broken pipe

EPROTO

Protocol error

EPROTOTYPE

Protocol wrong type for socket

EPROTONOSUPPORT

Unknown protocol

ERANGE

Result too large

EREMOTE

Resource is remote

EROFS

Read-only file system

ESHUTDOWN

Can’t send after socket shutdown

ESOCKTNOSUPPORT

Socket type not supported

ESPIPE

Illegal seek

ESRCH

No such process

ESRMNT

Srmount error

ESTRPIPE

Strings pipe error

ETIME

Stream ioctl timeout

ETIMEDOUT

Connection timed out

ETXTBSY

Text file busy

EWOULDBLOCK

Operation would block (usually same as EAGAIN)

EXDEV

Cross-device link

_strerror_r is a reentrant version of the above.

Returns
This function returns a pointer to a string. Your application must not modify that string.

Portability
ANSI C requires strerror, but does not specify the strings used for each error number.

strerror_l is POSIX-1.2008.

Although this implementation of strerror is reentrant (depending on _user_strerror), ANSI C declares that subsequent calls to strerror may overwrite the result string; therefore portable code cannot depend on the reentrancy of this subroutine.

Although this implementation of strerror guarantees a non-null result with a NUL-terminator, some implementations return NULL on failure. Although POSIX allows strerror to set errno to EINVAL on failure, this implementation does not do so (unless you provide _user_strerror).

POSIX recommends that unknown errnum result in a message including that value, however it is not a requirement and this implementation does not provide that information (unless you provide _user_strerror).

This implementation of strerror provides for user-defined extensibility. errno.h defines __ELASTERROR, which can be used as a base for user-defined error values. If the user supplies a routine named _user_strerror, and errnum passed to strerror does not match any of the supported values, _user_strerror is called with three arguments. The first is of type int, and is the errnum value unknown to strerror. The second is of type int, and matches the internal argument of _strerror_r; this should be zero if called from strerror and non-zero if called from any other function; _user_strerror can use this information to satisfy the POSIX rule that no other standardized function can overwrite a static buffer reused by strerror. The third is of type int *, and matches the error argument of _strerror_r; if a non-zero value is stored into that location (usually EINVAL), then strerror will set errno to that value, and the XPG variant of strerror_r will return that value instead of zero or ERANGE. _user_strerror returns a char * value; returning NULL implies that the user function did not choose to handle errnum. The default _user_strerror returns NULL for all input values. Note that _user_sterror must be thread-safe, and only denote errors via the third argument rather than modifying errno, if strerror and strerror_r are are to comply with POSIX.

strerror requires no supporting OS subroutines.