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8190a9ee | 1 | .\" Copyright 2005, 2012, 2016 Michael Kerrisk <mtk.manpages@gmail.com> |
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2 | .\" |
3 | .\" %%%LICENSE_START(GPL_NOVERSION_ONELINE) | |
4 | .\" Distributed under the GPL. | |
5 | .\" %%%LICENSE_END | |
6 | .\" | |
7 | .\" 2008-12-04, Petr Baudis <pasky@suse.cz>: Document open_wmemstream() | |
8 | .\" | |
4b8c67d9 | 9 | .TH OPEN_MEMSTREAM 3 2017-09-15 "GNU" "Linux Programmer's Manual" |
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10 | .SH NAME |
11 | open_memstream, open_wmemstream \- open a dynamic memory buffer stream | |
12 | .SH SYNOPSIS | |
13 | .nf | |
14 | .B #include <stdio.h> | |
f90f031e | 15 | .PP |
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16 | .BI "FILE *open_memstream(char **" ptr ", size_t *" sizeloc ); |
17 | ||
18 | .B #include <wchar.h> | |
f90f031e | 19 | .PP |
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20 | .BI "FILE *open_wmemstream(wchar_t **" ptr ", size_t *" sizeloc ); |
21 | .fi | |
68e4db0a | 22 | .PP |
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23 | .in -4n |
24 | Feature Test Macro Requirements for glibc (see | |
25 | .BR feature_test_macros (7)): | |
26 | .in | |
68e4db0a | 27 | .PP |
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28 | .BR open_memstream (), |
29 | .BR open_wmemstream (): | |
30 | .PD 0 | |
31 | .ad l | |
32 | .RS 4 | |
33 | .TP 4 | |
34 | Since glibc 2.10: | |
35 | _POSIX_C_SOURCE\ >=\ 200809L | |
36 | .TP | |
37 | Before glibc 2.10: | |
38 | _GNU_SOURCE | |
39 | .RE | |
40 | .ad | |
41 | .PD | |
42 | .SH DESCRIPTION | |
43 | The | |
44 | .BR open_memstream () | |
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45 | function opens a stream for writing to a memory buffer. |
46 | The function dynamically allocates the buffer, | |
47 | and the buffer automatically grows as needed. | |
e3d1b1b7 | 48 | Initially, the buffer has a size of zero. |
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49 | After closing the stream, the caller should |
50 | .BR free (3) | |
51 | this buffer. | |
847e0d88 | 52 | .PP |
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53 | The locations pointed to by |
54 | .IR ptr | |
55 | and | |
56 | .I sizeloc | |
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57 | are used to report, respectively, |
58 | the current location and the size of the buffer. | |
2c767761 | 59 | The locations referred to by these pointers are updated |
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60 | each time the stream is flushed |
61 | .RB ( fflush (3)) | |
62 | and when the stream is closed | |
63 | .RB ( fclose (3)). | |
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64 | These values remain valid only as long as the caller |
65 | performs no further output on the stream. | |
66 | If further output is performed, then the stream | |
207f4520 | 67 | must again be flushed before trying to access these values. |
847e0d88 | 68 | .PP |
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69 | A null byte is maintained at the end of the buffer. |
70 | This byte is | |
71 | .I not | |
72 | included in the size value stored at | |
73 | .IR sizeloc . | |
847e0d88 | 74 | .PP |
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75 | The stream maintains the notion of a current position, |
76 | which is initially zero (the start of the buffer). | |
77 | Each write operation implicitly adjusts the buffer position. | |
78 | The stream's buffer position can be explicitly changed with | |
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79 | .BR fseek (3) |
80 | or | |
81 | .BR fseeko (3). | |
82 | Moving the buffer position past the end | |
83 | of the data already written fills the intervening space with | |
207f4520 | 84 | null characters. |
847e0d88 | 85 | .PP |
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86 | The |
87 | .BR open_wmemstream () | |
88 | is similar to | |
89 | .BR open_memstream (), | |
90 | but operates on wide characters instead of bytes. | |
91 | .SH RETURN VALUE | |
92 | Upon successful completion, | |
93 | .BR open_memstream () | |
94 | and | |
95 | .BR open_wmemstream () | |
96 | return a | |
97 | .I FILE | |
98 | pointer. | |
99 | Otherwise, NULL is returned and | |
100 | .I errno | |
101 | is set to indicate the error. | |
102 | .SH VERSIONS | |
103 | .BR open_memstream () | |
104 | was already available in glibc 1.0.x. | |
105 | .BR open_wmemstream () | |
106 | is available since glibc 2.4. | |
107 | .SH ATTRIBUTES | |
108 | For an explanation of the terms used in this section, see | |
109 | .BR attributes (7). | |
110 | .TS | |
111 | allbox; | |
112 | lb lb lb | |
113 | l l l. | |
114 | Interface Attribute Value | |
115 | T{ | |
116 | .BR open_memstream (), | |
117 | .br | |
118 | .BR open_wmemstream | |
119 | T} Thread safety MT-Safe | |
120 | .TE | |
847e0d88 | 121 | .sp 1 |
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122 | .SH CONFORMING TO |
123 | POSIX.1-2008. | |
124 | These functions are not specified in POSIX.1-2001, | |
125 | and are not widely available on other systems. | |
126 | .SH NOTES | |
127 | There is no file descriptor associated with the file stream | |
128 | returned by these functions | |
129 | (i.e., | |
130 | .BR fileno (3) | |
131 | will return an error if called on the returned stream). | |
132 | .SH BUGS | |
133 | In glibc before version 2.7, seeking past the end of a stream created by | |
134 | .BR open_memstream () | |
135 | does not enlarge the buffer; instead the | |
136 | .BR fseek (3) | |
137 | call fails, returning \-1. | |
138 | .\" http://sourceware.org/bugzilla/show_bug.cgi?id=1996 | |
139 | .SH EXAMPLE | |
140 | See | |
141 | .BR fmemopen (3). | |
142 | .SH SEE ALSO | |
143 | .BR fmemopen (3), | |
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144 | .BR fopen (3), |
145 | .BR setbuf (3) |