error(3) — Linux manual page


error(3)                Library Functions Manual                error(3)

NAME         top

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

LIBRARY         top

       Standard C library (libc, -lc)

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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;
       otherwise it returns after printing the error message.

       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

       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.

ATTRIBUTES         top

       For an explanation of the terms used in this section, see
       │ 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 cancelation, so it can be interrupted
       only after one of the two variables is modified.  After that,
       error_at_line() is very much like error().

STANDARDS         top


SEE ALSO         top

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

COLOPHON         top

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Linux man-pages 6.9.1          2024-05-02                       error(3)

Pages that refer to this page: err(3)errno(3)perror(3)strerror(3)sysexits.h(3head)