1OPEN_MEMSTREAM(3) Linux Programmer's Manual OPEN_MEMSTREAM(3)
2
6 open_memstream, open_wmemstream - open a dynamic memory buffer stream
7
9 #include <stdio.h>
10 FILE *open_memstream(char **ptr, size_t *sizeloc);
12 #include <wchar.h>
14 FILE *open_wmemstream(wchar_t **ptr, size_t *sizeloc);
16 Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
18 open_memstream(), open_wmemstream():
20 Since glibc 2.10:
21 _POSIX_C_SOURCE >= 200809L
22 Before glibc 2.10:
23 _GNU_SOURCE
24
26 The open_memstream() function opens a stream for writing to a memory
27 buffer. The function dynamically allocates the buffer, and the buffer
28 automatically grows as needed. Initially, the buffer has a size of
29 zero. After closing the stream, the caller should free(3) this buffer.
30 The locations pointed to by ptr and sizeloc are used to report, respec‐
32 tively, the current location and the size of the buffer. The locations
33 referred to by these pointers are updated each time the stream is
34 flushed (fflush(3)) and when the stream is closed (fclose(3)). These
35 values remain valid only as long as the caller performs no further out‐
36 put on the stream. If further output is performed, then the stream
37 must again be flushed before trying to access these values.
38 A null byte is maintained at the end of the buffer. This byte is not
40 included in the size value stored at sizeloc.
41 The stream maintains the notion of a current position, which is ini‐
43 tially zero (the start of the buffer). Each write operation implicitly
44 adjusts the buffer position. The stream's buffer position can be ex‐
45 plicitly changed with fseek(3) or fseeko(3). Moving the buffer posi‐
46 tion past the end of the data already written fills the intervening
47 space with null characters.
48 The open_wmemstream() is similar to open_memstream(), but operates on
50 wide characters instead of bytes.
51
53 Upon successful completion, open_memstream() and open_wmemstream() re‐
54 turn a FILE pointer. Otherwise, NULL is returned and errno is set to
55 indicate the error.
56
58 open_memstream() was already available in glibc 1.0.x. open_wmem‐
59 stream() is available since glibc 2.4.
60
62 For an explanation of the terms used in this section, see at‐
63 tributes(7).
64 ┌──────────────────┬───────────────┬─────────┐
66 │Interface │ Attribute │ Value │
67 ├──────────────────┼───────────────┼─────────┤
68 │open_memstream(), │ Thread safety │ MT-Safe │
69 │open_wmemstream │ │ │
70 └──────────────────┴───────────────┴─────────┘
71
73 POSIX.1-2008. These functions are not specified in POSIX.1-2001, and
74 are not widely available on other systems.
75
77 There is no file descriptor associated with the file stream returned by
78 these functions (i.e., fileno(3) will return an error if called on the
79 returned stream).
80
82 In glibc before version 2.7, seeking past the end of a stream created
83 by open_memstream() does not enlarge the buffer; instead the fseek(3)
84 call fails, returning -1.
85
87 See fmemopen(3).
88
90 fmemopen(3), fopen(3), setbuf(3)
91
93 This page is part of release 5.10 of the Linux man-pages project. A
94 description of the project, information about reporting bugs, and the
95 latest version of this page, can be found at
96 https://www.kernel.org/doc/man-pages/.
97GNU 2020-06-09 OPEN_MEMSTREAM(3)