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ERROR(3) Linux Programmer's Manual ERROR(3)
NAME
error, error_at_line, error_message_count, error_one_per_line, error_print_progname - glibc error reporting functions
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 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 re‐
quired 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 er‐
ror(), 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 mes‐
sage 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 er‐
ror_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 vari‐
ables is modified. After that, error_at_line() is very much like error().
CONFORMING TO
These functions and variables are GNU extensions, and should not be used in programs intended to be portable.
SEE ALSO
err(3), errno(3), exit(3), perror(3), program_invocation_name(3), strerror(3)
GNU 2021-03-22 ERROR(3)