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       error,  error_at_line,  error_message_count,  error_one_per_line,  error_print_progname  -
       glibc error reporting functions


       #include <error.h>

       void error(int status, int errnum, const char *format, ...);

       void error_at_line(int status, int errnum, const char *filename,
                          unsigned int linenum, const char *format, ...);

       extern unsigned int error_message_count;

       extern int error_one_per_line;

       extern void (*error_print_progname) (void);


       error() is a general error-reporting function.  It flushes stdout,  and  then  outputs  to
       stderr the program name, a colon and a space, the message specified by the printf(3)-style
       format string format, and, if errnum is nonzero, a second colon and a  space  followed  by
       the  string  given  by  strerror(errnum).  Any arguments required for format should follow
       format in the argument list.  The output is terminated by a newline character.

       The  program  name  printed  by  error()   is   the   value   of   the   global   variable
       program_invocation_name(3).   program_invocation_name  initially  has  the  same  value as
       main()'s argv[0].  The value of this variable can be modified  to  change  the  output  of

       If  status  has a nonzero value, then error() calls exit(3) to terminate the program using
       the given value as the exit status.

       The error_at_line() function is exactly the same as error(), except for  the  addition  of
       the  arguments  filename  and linenum.  The output produced is as for error(), except that
       after the program name are written: a colon, the value of filename, a colon, and the value
       of  linenum.   The  preprocessor  values  __LINE__ and __FILE__ may be useful when calling
       error_at_line(), but other values can also be used.  For example,  these  arguments  could
       refer to a location in an input file.

       If  the  global  variable error_one_per_line is set nonzero, a sequence of error_at_line()
       calls with the same value of filename and linenum will result in  only  one  message  (the
       first) being output.

       The  global  variable  error_message_count  counts  the  number of messages that have been
       output by error() and error_at_line().

       If the global variable error_print_progname is assigned the address of a  function  (i.e.,
       is  not  NULL),  then  that  function  is called instead of prefixing the message with the
       program name and colon.  The function should print a suitable string to stderr.


       For an explanation of the terms used in this section, see attributes(7).

       │InterfaceAttributeValue                             │
       │error()         │ Thread safety │ MT-Safe locale                    │
       │error_at_line() │ Thread safety │ MT-Unsafe race:                   │
       │                │               │ error_at_line/error_one_per_line  │
       │                │               │ locale                            │
       The internal error_one_per_line variable is accessed (without any form of synchronization,
       but  since  it's an int used once, it should be safe enough) and, if error_one_per_line is
       set nonzero, the internal static variables (not exposed to users) used to  hold  the  last
       printed  filename  and  line number are accessed and modified without synchronization; the
       update is not atomic and it occurs before disabling cancellation, so it can be interrupted
       only after one of the two variables is modified.  After that, error_at_line() is very much
       like error().


       These functions and variables are GNU extensions, and  should  not  be  used  in  programs
       intended to be portable.


       err(3), errno(3), exit(3), perror(3), program_invocation_name(3), strerror(3)


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