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1 | .\" Copyright (c) 1994 Michael Haardt (michael@moria.de), 1994-06-04 |
2 | .\" Copyright (c) 1995 Michael Haardt | |
3 | .\" (michael@cantor.informatik.rwth-aachen.de), 1995-03-16 | |
4 | .\" Copyright (c) 1996 Andries Brouwer (aeb@cwi.nl), 1996-01-13 | |
5 | .\" | |
1dd72f9c | 6 | .\" %%%LICENSE_START(GPLv2+_DOC_FULL) |
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7 | .\" This is free documentation; you can redistribute it and/or |
8 | .\" modify it under the terms of the GNU General Public License as | |
9 | .\" published by the Free Software Foundation; either version 2 of | |
10 | .\" the License, or (at your option) any later version. | |
11 | .\" | |
12 | .\" The GNU General Public License's references to "object code" | |
13 | .\" and "executables" are to be interpreted as the output of any | |
14 | .\" document formatting or typesetting system, including | |
15 | .\" intermediate and printed output. | |
16 | .\" | |
17 | .\" This manual is distributed in the hope that it will be useful, | |
18 | .\" but WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | .\" MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the | |
20 | .\" GNU General Public License for more details. | |
21 | .\" | |
22 | .\" You should have received a copy of the GNU General Public | |
c715f741 MK |
23 | .\" License along with this manual; if not, see |
24 | .\" <http://www.gnu.org/licenses/>. | |
6a8d8745 | 25 | .\" %%%LICENSE_END |
fea681da MK |
26 | .\" |
27 | .\" 1996-01-13 aeb: merged in some text contributed by Melvin Smith | |
28 | .\" (msmith@falcon.mercer.peachnet.edu) and various other changes. | |
29 | .\" Modified 1996-05-16 by Martin Schulze (joey@infodrom.north.de) | |
30 | .\" | |
4b8c67d9 | 31 | .TH PERROR 3 2017-09-15 "" "Linux Programmer's Manual" |
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32 | .SH NAME |
33 | perror \- print a system error message | |
34 | .SH SYNOPSIS | |
35 | .B #include <stdio.h> | |
68e4db0a | 36 | .PP |
01038eba | 37 | .BI "void perror(const char *" s ); |
f90f031e | 38 | |
fea681da | 39 | .B #include <errno.h> |
68e4db0a | 40 | .PP |
6729be54 | 41 | .BI "const char * const " sys_errlist []; |
fea681da MK |
42 | .br |
43 | .BI "int " sys_nerr ; | |
44 | .br | |
e82a01da | 45 | .BI "int " errno "; \fR/* Not really declared this way; see errno(3) */" |
68e4db0a | 46 | .PP |
cc4615cc MK |
47 | .in -4n |
48 | Feature Test Macro Requirements for glibc (see | |
49 | .BR feature_test_macros (7)): | |
50 | .in | |
68e4db0a | 51 | .PP |
cc4615cc MK |
52 | .IR sys_errlist , |
53 | .IR sys_nerr : | |
51c612fb MK |
54 | Since glibc 2.19: |
55 | _DEFAULT_SOURCE | |
56 | Glibc 2.19 and earlier: | |
57 | _BSD_SOURCE | |
fea681da | 58 | .SH DESCRIPTION |
e82a01da | 59 | The |
63aa9df0 | 60 | .BR perror () |
e82a01da | 61 | function produces a message on standard error describing the last |
fea681da | 62 | error encountered during a call to a system or library function. |
847e0d88 | 63 | .PP |
fea681da MK |
64 | First (if |
65 | .I s | |
66 | is not NULL and | |
bd9b2a9c | 67 | .I *s |
e82a01da | 68 | is not a null byte (\(aq\\0\(aq)), the argument string |
fea681da MK |
69 | .I s |
70 | is printed, followed by a colon and a blank. | |
e82a01da MK |
71 | Then an error message corresponding to the current value of |
72 | .I errno | |
73 | and a new-line. | |
847e0d88 | 74 | .PP |
fea681da | 75 | To be of most use, the argument string should include the name |
c13182ef | 76 | of the function that incurred the error. |
847e0d88 | 77 | .PP |
fea681da | 78 | The global error list |
e82a01da MK |
79 | .IR sys_errlist "[]," |
80 | which can be indexed by | |
81 | .IR errno , | |
fea681da MK |
82 | can be used to obtain the error message without the newline. |
83 | The largest message number provided in the table is | |
b29f2872 | 84 | .IR sys_nerr "\-1." |
e82a01da | 85 | Be careful when directly accessing this list, because new error values |
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86 | may not have been added to |
87 | .IR sys_errlist "[]." | |
79038fa7 MK |
88 | The use of |
89 | .IR sys_errlist "[]" | |
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90 | is nowadays deprecated; use |
91 | .BR strerror (3) | |
3144b412 | 92 | instead. |
847e0d88 | 93 | .PP |
fea681da MK |
94 | When a system call fails, it usually returns \-1 and sets the |
95 | variable | |
96 | .I errno | |
c13182ef MK |
97 | to a value describing what went wrong. |
98 | (These values can be found in | |
a9a13a50 | 99 | .IR <errno.h> .) |
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100 | Many library functions do likewise. |
101 | The function | |
63aa9df0 | 102 | .BR perror () |
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103 | serves to translate this error code into human-readable form. |
104 | Note that | |
105 | .I errno | |
7e16fc97 | 106 | is undefined after a successful system call or library function call: |
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107 | this call may well change this variable, even though it succeeds, |
108 | for example because it internally used some other library function that failed. | |
109 | Thus, if a failing call is not immediately followed by a call to | |
e511ffb6 | 110 | .BR perror (), |
fea681da MK |
111 | the value of |
112 | .I errno | |
113 | should be saved. | |
80563762 ZL |
114 | .SH ATTRIBUTES |
115 | For an explanation of the terms used in this section, see | |
116 | .BR attributes (7). | |
117 | .TS | |
118 | allbox; | |
119 | lb lb lb | |
120 | l l l. | |
121 | Interface Attribute Value | |
122 | T{ | |
123 | .BR perror () | |
124 | T} Thread safety MT-Safe race:stderr | |
125 | .TE | |
847e0d88 | 126 | .sp 1 |
47297adb | 127 | .SH CONFORMING TO |
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128 | .BR perror (), |
129 | .IR errno : | |
99ee5719 | 130 | POSIX.1-2001, POSIX.1-2008, C89, C99, 4.3BSD. |
847e0d88 | 131 | .PP |
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132 | The externals |
133 | .I sys_nerr | |
134 | and | |
135 | .I sys_errlist | |
98ed7d1d | 136 | derive from BSD, but are not specified in POSIX.1. |
19c98696 | 137 | .SH NOTES |
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138 | The externals |
139 | .I sys_nerr | |
140 | and | |
141 | .I sys_errlist | |
142 | are defined by glibc, but in | |
143 | .IR <stdio.h> . | |
144 | .\" and only when _BSD_SOURCE is defined. | |
c3dfd2c8 | 145 | .\" When |
cc4615cc MK |
146 | .\" .B _GNU_SOURCE |
147 | .\" is defined, the symbols | |
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148 | .\" .I _sys_nerr |
149 | .\" and | |
150 | .\" .I _sys_errlist | |
151 | .\" are provided. | |
47297adb | 152 | .SH SEE ALSO |
d7871cf9 | 153 | .BR err (3), |
fea681da | 154 | .BR errno (3), |
37b6aec3 | 155 | .BR error (3), |
fea681da | 156 | .BR strerror (3) |