man3/error.3

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  26 .\"   glibc manual and source
  27 .TH error 3 (date) "Linux man-pages (unreleased)"
  28 .SH NAME
  29 error, error_at_line, error_message_count, error_one_per_line,
  30 error_print_progname \- glibc error reporting functions
  31 .SH LIBRARY
  32 Standard C library
  33 .RI ( libc ", " \-lc )
  34 .SH SYNOPSIS
  35 .nf
  36 .B #include <error.h>
  37 .PP
  38 .BI "void error(int " status ", int " errnum ", const char *" format ", ...);"
  39 .BI "void error_at_line(int " status ", int " errnum ", const char *" filename ,
  40 .BI "                   unsigned int " linenum ", const char *" format ", ...);"
  41 .PP
  42 .BI "extern unsigned int " error_message_count ;
  43 .BI "extern int " error_one_per_line ;
  44 .PP
  45 .BI "extern void (*" error_print_progname ")(void);"
  46 .fi
  47 .SH DESCRIPTION
  48 .BR error ()
  49 is a general error-reporting function.
  50 It flushes
  51 .IR stdout ,
  52 and then outputs to
  53 .I stderr
  54 the program name, a colon and a space, the message specified by the
  55 .BR printf (3)-style
  56 format string \fIformat\fP, and, if \fIerrnum\fP is
  57 nonzero, a second colon and a space followed by the string given by
  58 .IR strerror(errnum) .
  59 Any arguments required for
  60 .I format
  61 should follow
  62 .I format
  63 in the argument list.
  64 The output is terminated by a newline character.
  65 .PP
  66 The program name printed by
  67 .BR error ()
  68 is the value of the global variable
  69 .BR program_invocation_name (3).
  70 .I program_invocation_name
  71 initially has the same value as
  72 .IR main ()'s
  73 .IR argv[0] .
  74 The value of this variable can be modified to change the output of
  75 .BR error ().
  76 .PP
  77 If \fIstatus\fP has a nonzero value, then
  78 .BR error ()
  79 calls
  80 .BR exit (3)
  81 to terminate the program using the given value as the exit status;
  82 otherwise it returns after printing the error message.
  83 .PP
  84 The
  85 .BR error_at_line ()
  86 function is exactly the same as
  87 .BR error (),
  88 except for the addition of the arguments
  89 .I filename
  90 and
  91 .IR linenum .
  92 The output produced is as for
  93 .BR error (),
  94 except that after the program name are written: a colon, the value of
  95 .IR filename ,
  96 a colon, and the value of
  97 .IR linenum .
  98 The preprocessor values \fB__LINE__\fP and
  99 \fB__FILE__\fP may be useful when calling
 100 .BR error_at_line (),
 101 but other values can also be used.
 102 For example, these arguments could refer to a location in an input file.
 103 .PP
 104 If the global variable \fIerror_one_per_line\fP is set nonzero,
 105 a sequence of
 106 .BR error_at_line ()
 107 calls with the
 108 same value of \fIfilename\fP and \fIlinenum\fP will result in only
 109 one message (the first) being output.
 110 .PP
 111 The global variable \fIerror_message_count\fP counts the number of
 112 messages that have been output by
 113 .BR error ()
 114 and
 115 .BR error_at_line ().
 116 .PP
 117 If the global variable \fIerror_print_progname\fP
 118 is assigned the address of a function
 119 (i.e., is not NULL), then that function is called
 120 instead of prefixing the message with the program name and colon.
 121 The function should print a suitable string to
 122 .IR stderr .
 123 .SH ATTRIBUTES
 124 For an explanation of the terms used in this section, see
 125 .BR attributes (7).
 126 .ad l
 127 .nh
 128 .TS
 129 allbox;
 130 lb lb lbx
 131 l l l.
 132 Interface       Attribute       Value
 133 T{
 134 .BR error ()
 135 T}      Thread safety   MT-Safe locale
 136 T{
 137 .BR error_at_line ()
 138 T}      Thread safety   T{
 139 MT-Unsafe\ race: error_at_line/\:error_one_per_line locale
 140 T}
 141 .TE
 142 .hy
 143 .ad
 144 .sp 1
 145 .PP
 146 The internal
 147 .I error_one_per_line
 148 variable is accessed (without any form of synchronization, but since it's an
 149 .I int
 150 used once, it should be safe enough) and, if
 151 .I error_one_per_line
 152 is set nonzero, the internal static variables (not exposed to users)
 153 used to hold the last printed filename and line number are accessed
 154 and modified without synchronization; the update is not atomic and it
 155 occurs before disabling cancelation, so it can be interrupted only after
 156 one of the two variables is modified.
 157 After that,
 158 .BR error_at_line ()
 159 is very much like
 160 .BR error ().
 161 .SH STANDARDS
 162 These functions and variables are GNU extensions, and should not be
 163 used in programs intended to be portable.
 164 .SH SEE ALSO
 165 .BR err (3),
 166 .BR errno (3),
 167 .BR exit (3),
 168 .BR perror (3),
 169 .BR program_invocation_name (3),
 170 .BR strerror (3)