error, error_at_line, error_message_count, error_one_per_line,
error_print_progname - glibc error reporting functions
Standard C library (
libc,
-lc)
#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; 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 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 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().
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)