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STRERROR(3)		     Library Functions Manual		     STRERROR(3)

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

LIBRARY
     Standard C Library (libc, -lc)

SYNOPSIS
     #include <stdio.h>

     void
     perror(const char *string);

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

     #include <string.h>

     char *
     strerror(int errnum);

     char *
     strerror_l(int errnum, locale_t);

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

DESCRIPTION
     The strerror(), strerror_l(), 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 corresponding message string in the current locale.  str-
     error() is not thread-safe.  It returns a pointer	to  an	internal  static
     buffer that could be overwritten by a strerror() call from another thread.

     The  strerror_l()	function  accepts  errnum error number and locale locale
     handle arguments and returns a pointer to a  string  corresponding  to  the
     specified	error in the given locale.  strerror_l() is thread-safe, its re-
     sult can be only overwritten by another call to strerror_l() from the  cur-
     rent thread.

     The strerror_r() function renders the same result into strerrbuf for a max-
     imum 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 string is
     non-NULL and does not point to the null character, this string is prepended
     to the message 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 mes-
     sage  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.  The number 0 is also recognized, although applica-
     tions that take advantage of this are likely to use unspecified  values  of
     errno.

     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(), str-
     error_l(), or strerror_r() should be used instead.

EXAMPLES
     The following example shows how to use perror() to report an error.

       #include <fcntl.h>
       #include <stdio.h>
       #include <stdlib.h>

       int
       main(void)
       {
	       int fd;

	       if ((fd = open("/nonexistent", O_RDONLY)) == -1) {
		       perror("open()");
		       exit(1);
	       }
	       printf("File descriptor: %d\n", fd);
	       return (0);
       }

     When  executed,  the program will print an error message along the lines of
     `open(): No such file or directory'.

SEE ALSO
     intro(2), err(3), 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").  The strerror_l() function conforms to  IEEE	Std  1003.1-2008
     ("POSIX.1").

HISTORY
     The  strerror()  and perror() functions first appeared in 4.4BSD.	The str-
     error_r()	function  was  implemented  in	FreeBSD  4.4   by   Wes   Peters
     <wes@FreeBSD.org>.  The strerror_l() function was added in FreeBSD 13.0.

BUGS
     The strerror() function returns its result in a static buffer which will be
     overwritten by subsequent calls.

     Programs that use the deprecated sys_errlist variable often fail to compile
     because  they  declare  it  inconsistently.  Size of the sys_errlist object
     might increase during FreeBSD lifetime, breaking some ABI stability guaran-
     tees.

FreeBSD ports 15.1		December 17, 2020		     STRERROR(3)

Want to link to this manual page? Use this URL:
<https://man.freebsd.org/cgi/man.cgi?query=perror&sektion=3&manpath=FreeBSD+15.1-RELEASE+and+Ports>

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