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STRERROR(3)              BSD Library Functions Manual              STRERROR(3)

NAME
     perror, strerror, strerror_r, sys_errlist, sys_nerr -- system error messages

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdio.h>

     void
     perror(const char *s);

     extern const char * const sys_errlist[];
     extern const int sys_nerr;

     #include <string.h>

     char *
     strerror(int errnum);

     int
     strerror_r(int errnum, char *strerrbuf, size_t buflen);

DESCRIPTION
     The strerror(), strerror_r(), and perror() functions look up the error message string corresponding to
     an error number.

     The strerror() function accepts an error number argument errnum and returns a pointer to the corre-sponding corresponding
     sponding message string.

     The strerror_r() function renders the same result into strerrbuf for a maximum of buflen characters and
     returns 0 upon success.

     The perror() function finds the error message corresponding to the current value of the global variable
     errno (intro(2)) and writes it, followed by a newline, to the standard error file descriptor.  If the
     argument s is non-NULL and does not point to the null character, this string is prepended to the mes-sage message
     sage string and separated from it by a colon and space (``: ''); otherwise, only the error message
     string is printed.

     If the error number is not recognized, these functions return an error message string containing
     ``Unknown error: '' followed by the error number in decimal.  The strerror() and strerror_r() functions
     return EINVAL as a warning.  Error numbers recognized by this implementation fall in the range 0 <=
     errnum < sys_nerr.

     If insufficient storage is provided in strerrbuf (as specified in buflen) to contain the error string,
     strerror_r() returns ERANGE and strerrbuf will contain an error message that has been truncated and NUL
     terminated to fit the length specified by buflen.

     The message strings can be accessed directly using the external array sys_errlist.  The external value
     sys_nerr contains a count of the messages in sys_errlist.  The use of these variables is deprecated;
     strerror() or strerror_r() should be used instead.

SEE ALSO
     intro(2), psignal(3)

STANDARDS
     The perror() and strerror() functions conform to ISO/IEC 9899:1999 (``ISO C99'').  The strerror_r()
     function conforms to IEEE Std 1003.1-2001 (``POSIX.1'').

HISTORY
     The strerror() and perror() functions first appeared in 4.4BSD.  The strerror_r() function was imple-
     mented in FreeBSD 4.4 by Wes Peters <wes@FreeBSD.org>.

BUGS
     For unknown error numbers, the strerror() function will return its result in a static buffer which may
     be overwritten by subsequent calls.

     The return type for strerror() is missing a type-qualifier; it should actually be const char *.

     Programs that use the deprecated sys_errlist variable often fail to compile because they declare it
     inconsistently.

BSD                            October 12, 2004                            BSD

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