NAME
strerror, strerrorr - return string describing error number SYNOPSIS
#include
char *strerror(int errnum); int strerrorr(int errnum, char *buf, sizet buflen); /* XSI-compliant */ char *strerrorr(int errnum, char *buf, sizet buflen);
/* GNU-specific */ Feature Test Macro Requirements for glibc (see featuretestmacros(7)):
The XSI-compliant version of strerrorr() is provided if: (POSIXCSOURCE >= 200112L || XOPENSOURCE >= 600) && ! GNUSOURCE
Otherwise, the GNU-specific version is provided. DESCRIPTION The strerror() function returns a pointer to a string that describes the error code passed in the argument errnum, possibly using the LCMESSAGES part of the current locale to select the appropriate lan‐ guage. (For example, if errnum is EINVAL, the returned description will "Invalid argument".) This string must not be modified by the application, but may be modified by a subsequent call to strerror(). No library function, including perror(3), will modify this string. The strerrorr() function is similar to strerror(), but is thread safe.
This function is available in two versions: an XSI-compliant version
specified in POSIX.1-2001 (available since glibc 2.3.4, but not POSIX-
compliant until glibc 2.13), and a GNU-specific version (available
since glibc 2.0). The XSI-compliant version is provided with the fea‐
ture test macros settings shown in the SYNOPSIS; otherwise the GNU-spe‐ cific version is provided. If no feature test macros are explicitly defined, then (since glibc 2.4) POSIXSOURCE is defined by default
with the value 200112L, so that the XSI-compliant version of str‐ errorr() is provided by default.
The XSI-compliant strerrorr() is preferred for portable applications.
It returns the error string in the user-supplied buffer buf of length buflen.
The GNU-specific strerrorr() returns a pointer to a string containing the error message. This may be either a pointer to a string that the function stores in buf, or a pointer to some (immutable) static string (in which case buf is unused). If the function stores a string in buf, then at most buflen bytes are stored (the string may be truncated if buflen is too small and errnum is unknown). The string always includes a terminating null byte ('\0'). RETURN VALUE
The strerror() and the GNU-specific strerrorr() functions return the appropriate error description string, or an "Unknown error nnn" message if the error number is unknown.
POSIX.1-2001 and POSIX.1-2008 require that a successful call to str‐ error() shall leave errno unchanged, and note that, since no function return value is reserved to indicate an error, an application that wishes to check for errors should initialize errno to zero before the call, and then check errno after the call.
The XSI-compliant strerrorr() function returns 0 on success. On
error, a (positive) error number is returned (since glibc 2.13), or -1 is returned and errno is set to indicate the error (glibc versions before 2.13). ERRORS EINVAL The value of errnum is not a valid error number. ERANGE Insufficient storage was supplied to contain the error descrip‐ tion string. ATTRIBUTES Multithreading (see pthreads(7))
The strerror() function is not thread-safe.
The strerrorr() function is thread-safe. ATTRIBUTES For an explanation of the terms used in this section, see attributes(7). ┌───────────────────────────┬───────────────┬─────────────────────────┐ │Interface │ Attribute │ Value │ ├───────────────────────────┼───────────────┼─────────────────────────┤
│strerror() │ Thread safety │ MT-Unsafe race:strerror │ ├───────────────────────────┼───────────────┼─────────────────────────┤
│strerrorr(), strerrorl() │ Thread safety │ MT-Safe │ └───────────────────────────┴───────────────┴─────────────────────────┘ VERSIONS The strerrorl() function first appeared in glibc 2.6. CONFORMING TO
strerror() is specified by POSIX.1-2001, C89, C99. strerrorr() is
specified by POSIX.1-2001.
The GNU-specific strerrorr() function is a nonstandard extension.
POSIX.1-2001 permits strerror() to set errno if the call encounters an error, but does not specify what value should be returned as the func‐ tion result in the event of an error. On some systems, strerror() returns NULL if the error number is unknown. On other systems, str‐ error() returns a string something like "Error nnn occurred" and sets
errno to EINVAL if the error number is unknown. C99 and POSIX.1-2008
require the return value to be non-NULL. SEE ALSO err(3), errno(3), error(3), perror(3), strsignal(3) COLOPHON
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be found at http://www.kernel.org/doc/man-pages/.
2013-06-21 STRERROR(3)