error(3) Library Functions Manual error(3)
NAME
error, error_at_line, error_message_count, error_one_per_line, er-
ror_print_progname - glibc error reporting functions
LIBRARY
Standard C library (libc, -lc)
SYNOPSIS
#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
error() is a general error-reporting function. It flushes stdout, and
then outputs to stderr the program name, a colon and a space, the mes-
sage specified by the printf(3)-style format string format, and, if er-
rnum 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 modi-
fied 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 re-
turns 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 er-
ror_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.
ATTRIBUTES
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 cancelation, so it
can be interrupted only after one of the two variables is modified. Af-
ter that, error_at_line() is very much like error().
STANDARDS
GNU.
SEE ALSO
err(3), errno(3), exit(3), perror(3), program_invocation_name(3), str-
error(3)
Linux man-pages 6.9.1 2024-05-02 error(3)
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