Provided by: manpages-dev_6.15-1_all 
NAME
error, error_at_line, error_message_count, error_one_per_line, error_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 *file,
unsigned int line, const char *format, ...);
extern unsigned int error_message_count;
extern int error_one_per_line;
extern typeof(void (void)) *error_print_progname;
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 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
file and line. The output produced is as for error(), except that after the program name are written: a
colon, the value of file, a colon, and the value of line. 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 file and line 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. After 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), strerror(3)
Linux man-pages 6.15 2025-06-05 error(3)