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Manual for perror - man 3 perror

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PERROR(3)                      Library functions                     PERROR(3)

       perror(1,3) - print a system error(8,n) message

       #include <stdio.h>

       void perror(1,3)(const char *s);

       #include <errno.h>

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

       The  routine  perror(1,3)() produces a message on the standard error(8,n) output,
       describing the last error(8,n) encountered during a  call  to  a  system  or
       library function.  First (if(3,n) s is not NULL and *s is not NUL) the argu-
       ment string(3,n) s is printed, followed by a colon and a  blank.   Then  the
       message and a new-line.

       To  be  of most use, the argument string(3,n) should include the name of the
       function that incurred the error.  The error(8,n) number is taken  from  the
       external variable errno, which is set(7,n,1 builtins) when errors occur but not cleared
       when non-erroneous calls are made.

       The global error(8,n) list sys_errlist[] indexed by errno  can  be  used  to
       obtain the error(8,n) message without the newline.  The largest message num-
       ber provided in(1,8) the table is sys_nerr -1.   Be  careful  when  directly
       accessing this list because new error(8,n) values may not have been added to

       When a system call fails, it usually returns -1 and sets  the  variable
       errno to a value describing what went wrong. (These values can be found
       in(1,8) <errno.h>.)  Many library functions do likewise.  The function  per-
       ror()  serves  to  translate  this error(8,n) code into human-readable form.
       Note that errno is undefined after a successful library call: this call
       may  well  change  this  variable, even though it succeeds, for example
       because it internally used some other  library  function  that  failed.
       Thus,  if(3,n)  a failing call is not immediately followed by a call to per-
       ror, the value of errno should be saved.

       The function perror(1,3)() and the external errno (see errno(3)) conform  to
       ANSI C, BSD 4.3, POSIX, X/OPEN.  The externals sys_nerr and sys_errlist
       conform to BSD.

       The externals sys_nerr and sys_errlist are defined  by  glibc,  but  in(1,8)

       errno(3), strerror(3)

                                  2001-12-14                         PERROR(3)

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