ERROR(3)                    Linux Programmer's Manual                   ERROR(3)

       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 error().

       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).

       │Interface       Attribute     Value                             │
       │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),

       This page is part of release 5.10 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

GNU                                2017-09-15                           ERROR(3)