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STRERROR(3) Linux Programmer's Manual STRERROR(3) NAME strerror, strerror_r - return string describing error number SYNOPSIS #include <string.h> char *strerror(int errnum); char *strerror_r(int errnum, char *buf, size_t buflen); Feature Test Macro Requirements for glibc (see feature_test_macros(7)): The XSI-compliant version of strerror_r() is provided if: (_POSIX_C_SOURCE >= 200112L || _XOPEN_SOURCE >= 600) && ! _GNU_SOURCE DESCRIPTION The strerror() function returns a string describing the error code passed in the argument errnum, possibly using the LC_MESSAGES part of the current locale to select the appropriate language. This string must not be modified by the application, but may be modified by a sub- sequent call to perror(3) or strerror(). No library function will mod- ify this string. The strerror_r() 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), and a GNU-spe- cific version (available since glibc 2.0). The XSI-compliant version is provided with the feature test macros settings shown in the SYNOP- SIS; otherwise the GNU-specific version is provided. If no feature test macros are explicitly defined, then (since glibc 2.4) _POSIX_SOURCE is defined by default with the value 200112L, so that the XSI-compliant version of strerror_r() is provided by default. The XSI-compliant strerror_r() is preferred for portable applications. It returns the error string in the user-supplied buffer buf of length buflen. The GNU-specific strerror_r() 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 the string always includes a terminating null byte. RETURN VALUE The strerror() and strerror_r() functions return the appropriate error description string, or an "Unknown error nnn" message if the error num- ber is unknown. The XSI-compliant strerror_r() function returns 0 on success; on error, -1 is returned and errno is set to indicate the error. ERRORS EINVAL The value of errnum is not a valid error number. ERANGE Insufficient storage was supplied to contain the error descrip- tion string. CONFORMING TO strerror() is specified by POSIX.1-2001, C89, C99. strerror_r() is specified by POSIX.1-2001. The GNU-specific strerror_r() function is a non-standard 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. SEE ALSO err(3), errno(3), error(3), perror(3), strsignal(3) 2007-07-26 STRERROR(3)