[444] | 1 | /* Copyright (C) 2007 Eric Blake |
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| 2 | * Permission to use, copy, modify, and distribute this software |
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| 3 | * is freely granted, provided that this notice is preserved. |
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| 4 | */ |
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| 5 | |
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| 6 | /* |
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| 7 | FUNCTION |
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| 8 | <<fmemopen>>---open a stream around a fixed-length string |
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| 9 | |
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| 10 | INDEX |
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| 11 | fmemopen |
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| 12 | |
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| 13 | SYNOPSIS |
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| 14 | #include <stdio.h> |
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| 15 | FILE *fmemopen(void *restrict <[buf]>, size_t <[size]>, |
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| 16 | const char *restrict <[mode]>); |
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| 17 | |
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| 18 | DESCRIPTION |
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| 19 | <<fmemopen>> creates a seekable <<FILE>> stream that wraps a |
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| 20 | fixed-length buffer of <[size]> bytes starting at <[buf]>. The stream |
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| 21 | is opened with <[mode]> treated as in <<fopen>>, where append mode |
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| 22 | starts writing at the first NUL byte. If <[buf]> is NULL, then |
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| 23 | <[size]> bytes are automatically provided as if by <<malloc>>, with |
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| 24 | the initial size of 0, and <[mode]> must contain <<+>> so that data |
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| 25 | can be read after it is written. |
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| 26 | |
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| 27 | The stream maintains a current position, which moves according to |
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| 28 | bytes read or written, and which can be one past the end of the array. |
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| 29 | The stream also maintains a current file size, which is never greater |
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| 30 | than <[size]>. If <[mode]> starts with <<r>>, the position starts at |
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| 31 | <<0>>, and file size starts at <[size]> if <[buf]> was provided. If |
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| 32 | <[mode]> starts with <<w>>, the position and file size start at <<0>>, |
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| 33 | and if <[buf]> was provided, the first byte is set to NUL. If |
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| 34 | <[mode]> starts with <<a>>, the position and file size start at the |
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| 35 | location of the first NUL byte, or else <[size]> if <[buf]> was |
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| 36 | provided. |
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| 37 | |
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| 38 | When reading, NUL bytes have no significance, and reads cannot exceed |
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| 39 | the current file size. When writing, the file size can increase up to |
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| 40 | <[size]> as needed, and NUL bytes may be embedded in the stream (see |
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| 41 | <<open_memstream>> for an alternative that automatically enlarges the |
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| 42 | buffer). When the stream is flushed or closed after a write that |
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| 43 | changed the file size, a NUL byte is written at the current position |
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| 44 | if there is still room; if the stream is not also open for reading, a |
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| 45 | NUL byte is additionally written at the last byte of <[buf]> when the |
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| 46 | stream has exceeded <[size]>, so that a write-only <[buf]> is always |
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| 47 | NUL-terminated when the stream is flushed or closed (and the initial |
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| 48 | <[size]> should take this into account). It is not possible to seek |
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| 49 | outside the bounds of <[size]>. A NUL byte written during a flush is |
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| 50 | restored to its previous value when seeking elsewhere in the string. |
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| 51 | |
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| 52 | RETURNS |
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| 53 | The return value is an open FILE pointer on success. On error, |
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| 54 | <<NULL>> is returned, and <<errno>> will be set to EINVAL if <[size]> |
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| 55 | is zero or <[mode]> is invalid, ENOMEM if <[buf]> was NULL and memory |
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| 56 | could not be allocated, or EMFILE if too many streams are already |
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| 57 | open. |
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| 58 | |
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| 59 | PORTABILITY |
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| 60 | This function is being added to POSIX 200x, but is not in POSIX 2001. |
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| 61 | |
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| 62 | Supporting OS subroutines required: <<sbrk>>. |
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| 63 | */ |
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| 64 | |
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| 65 | #include <stdio.h> |
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| 66 | #include <errno.h> |
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| 67 | #include <string.h> |
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| 68 | #include <sys/lock.h> |
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| 69 | #include "local.h" |
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| 70 | |
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| 71 | /* Describe details of an open memstream. */ |
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| 72 | typedef struct fmemcookie { |
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| 73 | void *storage; /* storage to free on close */ |
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| 74 | char *buf; /* buffer start */ |
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| 75 | size_t pos; /* current position */ |
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| 76 | size_t eof; /* current file size */ |
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| 77 | size_t max; /* maximum file size */ |
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| 78 | char append; /* nonzero if appending */ |
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| 79 | char writeonly; /* 1 if write-only */ |
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| 80 | char saved; /* saved character that lived at pos before write-only NUL */ |
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| 81 | } fmemcookie; |
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| 82 | |
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| 83 | /* Read up to non-zero N bytes into BUF from stream described by |
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| 84 | COOKIE; return number of bytes read (0 on EOF). */ |
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| 85 | static _READ_WRITE_RETURN_TYPE |
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| 86 | fmemreader (struct _reent *ptr, |
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| 87 | void *cookie, |
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| 88 | char *buf, |
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| 89 | _READ_WRITE_BUFSIZE_TYPE n) |
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| 90 | { |
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| 91 | fmemcookie *c = (fmemcookie *) cookie; |
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| 92 | /* Can't read beyond current size, but EOF condition is not an error. */ |
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| 93 | if (c->pos > c->eof) |
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| 94 | return 0; |
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| 95 | if (n >= c->eof - c->pos) |
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| 96 | n = c->eof - c->pos; |
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| 97 | memcpy (buf, c->buf + c->pos, n); |
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| 98 | c->pos += n; |
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| 99 | return n; |
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| 100 | } |
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| 101 | |
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| 102 | /* Write up to non-zero N bytes of BUF into the stream described by COOKIE, |
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| 103 | returning the number of bytes written or EOF on failure. */ |
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| 104 | static _READ_WRITE_RETURN_TYPE |
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| 105 | fmemwriter (struct _reent *ptr, |
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| 106 | void *cookie, |
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| 107 | const char *buf, |
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| 108 | _READ_WRITE_BUFSIZE_TYPE n) |
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| 109 | { |
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| 110 | fmemcookie *c = (fmemcookie *) cookie; |
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| 111 | int adjust = 0; /* true if at EOF, but still need to write NUL. */ |
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| 112 | |
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| 113 | /* Append always seeks to eof; otherwise, if we have previously done |
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| 114 | a seek beyond eof, ensure all intermediate bytes are NUL. */ |
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| 115 | if (c->append) |
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| 116 | c->pos = c->eof; |
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| 117 | else if (c->pos > c->eof) |
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| 118 | memset (c->buf + c->eof, '\0', c->pos - c->eof); |
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| 119 | /* Do not write beyond EOF; saving room for NUL on write-only stream. */ |
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| 120 | if (c->pos + n > c->max - c->writeonly) |
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| 121 | { |
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| 122 | adjust = c->writeonly; |
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| 123 | n = c->max - c->pos; |
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| 124 | } |
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| 125 | /* Now n is the number of bytes being modified, and adjust is 1 if |
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| 126 | the last byte is NUL instead of from buf. Write a NUL if |
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| 127 | write-only; or if read-write, eof changed, and there is still |
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| 128 | room. When we are within the file contents, remember what we |
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| 129 | overwrite so we can restore it if we seek elsewhere later. */ |
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| 130 | if (c->pos + n > c->eof) |
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| 131 | { |
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| 132 | c->eof = c->pos + n; |
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| 133 | if (c->eof - adjust < c->max) |
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| 134 | c->saved = c->buf[c->eof - adjust] = '\0'; |
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| 135 | } |
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| 136 | else if (c->writeonly) |
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| 137 | { |
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| 138 | if (n) |
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| 139 | { |
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| 140 | c->saved = c->buf[c->pos + n - adjust]; |
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| 141 | c->buf[c->pos + n - adjust] = '\0'; |
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| 142 | } |
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| 143 | else |
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| 144 | adjust = 0; |
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| 145 | } |
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| 146 | c->pos += n; |
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| 147 | if (n - adjust) |
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| 148 | memcpy (c->buf + c->pos - n, buf, n - adjust); |
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| 149 | else |
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| 150 | { |
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| 151 | ptr->_errno = ENOSPC; |
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| 152 | return EOF; |
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| 153 | } |
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| 154 | return n; |
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| 155 | } |
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| 156 | |
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| 157 | /* Seek to position POS relative to WHENCE within stream described by |
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| 158 | COOKIE; return resulting position or fail with EOF. */ |
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| 159 | static _fpos_t |
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| 160 | fmemseeker (struct _reent *ptr, |
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| 161 | void *cookie, |
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| 162 | _fpos_t pos, |
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| 163 | int whence) |
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| 164 | { |
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| 165 | fmemcookie *c = (fmemcookie *) cookie; |
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| 166 | #ifndef __LARGE64_FILES |
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| 167 | off_t offset = (off_t) pos; |
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| 168 | #else /* __LARGE64_FILES */ |
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| 169 | _off64_t offset = (_off64_t) pos; |
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| 170 | #endif /* __LARGE64_FILES */ |
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| 171 | |
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| 172 | if (whence == SEEK_CUR) |
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| 173 | offset += c->pos; |
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| 174 | else if (whence == SEEK_END) |
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| 175 | offset += c->eof; |
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| 176 | if (offset < 0) |
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| 177 | { |
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| 178 | ptr->_errno = EINVAL; |
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| 179 | offset = -1; |
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| 180 | } |
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| 181 | else if (offset > c->max) |
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| 182 | { |
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| 183 | ptr->_errno = ENOSPC; |
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| 184 | offset = -1; |
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| 185 | } |
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| 186 | #ifdef __LARGE64_FILES |
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| 187 | else if ((_fpos_t) offset != offset) |
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| 188 | { |
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| 189 | ptr->_errno = EOVERFLOW; |
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| 190 | offset = -1; |
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| 191 | } |
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| 192 | #endif /* __LARGE64_FILES */ |
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| 193 | else |
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| 194 | { |
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| 195 | if (c->writeonly && c->pos < c->eof) |
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| 196 | { |
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| 197 | c->buf[c->pos] = c->saved; |
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| 198 | c->saved = '\0'; |
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| 199 | } |
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| 200 | c->pos = offset; |
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| 201 | if (c->writeonly && c->pos < c->eof) |
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| 202 | { |
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| 203 | c->saved = c->buf[c->pos]; |
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| 204 | c->buf[c->pos] = '\0'; |
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| 205 | } |
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| 206 | } |
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| 207 | return (_fpos_t) offset; |
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| 208 | } |
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| 209 | |
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| 210 | /* Seek to position POS relative to WHENCE within stream described by |
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| 211 | COOKIE; return resulting position or fail with EOF. */ |
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| 212 | #ifdef __LARGE64_FILES |
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| 213 | static _fpos64_t |
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| 214 | fmemseeker64 (struct _reent *ptr, |
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| 215 | void *cookie, |
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| 216 | _fpos64_t pos, |
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| 217 | int whence) |
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| 218 | { |
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| 219 | _off64_t offset = (_off64_t) pos; |
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| 220 | fmemcookie *c = (fmemcookie *) cookie; |
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| 221 | if (whence == SEEK_CUR) |
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| 222 | offset += c->pos; |
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| 223 | else if (whence == SEEK_END) |
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| 224 | offset += c->eof; |
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| 225 | if (offset < 0) |
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| 226 | { |
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| 227 | ptr->_errno = EINVAL; |
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| 228 | offset = -1; |
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| 229 | } |
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| 230 | else if (offset > c->max) |
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| 231 | { |
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| 232 | ptr->_errno = ENOSPC; |
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| 233 | offset = -1; |
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| 234 | } |
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| 235 | else |
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| 236 | { |
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| 237 | if (c->writeonly && c->pos < c->eof) |
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| 238 | { |
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| 239 | c->buf[c->pos] = c->saved; |
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| 240 | c->saved = '\0'; |
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| 241 | } |
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| 242 | c->pos = offset; |
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| 243 | if (c->writeonly && c->pos < c->eof) |
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| 244 | { |
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| 245 | c->saved = c->buf[c->pos]; |
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| 246 | c->buf[c->pos] = '\0'; |
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| 247 | } |
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| 248 | } |
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| 249 | return (_fpos64_t) offset; |
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| 250 | } |
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| 251 | #endif /* __LARGE64_FILES */ |
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| 252 | |
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| 253 | /* Reclaim resources used by stream described by COOKIE. */ |
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| 254 | static int |
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| 255 | fmemcloser (struct _reent *ptr, |
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| 256 | void *cookie) |
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| 257 | { |
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| 258 | fmemcookie *c = (fmemcookie *) cookie; |
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| 259 | _free_r (ptr, c->storage); |
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| 260 | return 0; |
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| 261 | } |
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| 262 | |
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| 263 | /* Open a memstream around buffer BUF of SIZE bytes, using MODE. |
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| 264 | Return the new stream, or fail with NULL. */ |
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| 265 | FILE * |
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| 266 | _fmemopen_r (struct _reent *ptr, |
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| 267 | void *__restrict buf, |
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| 268 | size_t size, |
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| 269 | const char *__restrict mode) |
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| 270 | { |
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| 271 | FILE *fp; |
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| 272 | fmemcookie *c; |
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| 273 | int flags; |
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| 274 | int dummy; |
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| 275 | |
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| 276 | if ((flags = __sflags (ptr, mode, &dummy)) == 0) |
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| 277 | return NULL; |
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| 278 | if (!size || !(buf || flags & __SRW)) |
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| 279 | { |
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| 280 | ptr->_errno = EINVAL; |
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| 281 | return NULL; |
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| 282 | } |
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| 283 | if ((fp = __sfp (ptr)) == NULL) |
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| 284 | return NULL; |
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| 285 | if ((c = (fmemcookie *) _malloc_r (ptr, sizeof *c + (buf ? 0 : size))) |
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| 286 | == NULL) |
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| 287 | { |
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| 288 | _newlib_sfp_lock_start (); |
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| 289 | fp->_flags = 0; /* release */ |
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| 290 | #ifndef __SINGLE_THREAD__ |
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| 291 | __lock_close_recursive (fp->_lock); |
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| 292 | #endif |
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| 293 | _newlib_sfp_lock_end (); |
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| 294 | return NULL; |
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| 295 | } |
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| 296 | |
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| 297 | c->storage = c; |
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| 298 | c->max = size; |
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| 299 | /* 9 modes to worry about. */ |
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| 300 | /* w/a, buf or no buf: Guarantee a NUL after any file writes. */ |
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| 301 | c->writeonly = (flags & __SWR) != 0; |
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| 302 | c->saved = '\0'; |
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| 303 | if (!buf) |
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| 304 | { |
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| 305 | /* r+/w+/a+, and no buf: file starts empty. */ |
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| 306 | c->buf = (char *) (c + 1); |
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| 307 | c->buf[0] = '\0'; |
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| 308 | c->pos = c->eof = 0; |
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| 309 | c->append = (flags & __SAPP) != 0; |
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| 310 | } |
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| 311 | else |
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| 312 | { |
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| 313 | c->buf = (char *) buf; |
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| 314 | switch (*mode) |
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| 315 | { |
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| 316 | case 'a': |
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| 317 | /* a/a+ and buf: position and size at first NUL. */ |
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| 318 | buf = memchr (c->buf, '\0', size); |
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| 319 | c->eof = c->pos = buf ? (char *) buf - c->buf : size; |
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| 320 | if (!buf && c->writeonly) |
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| 321 | /* a: guarantee a NUL within size even if no writes. */ |
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| 322 | c->buf[size - 1] = '\0'; |
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| 323 | c->append = 1; |
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| 324 | break; |
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| 325 | case 'r': |
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| 326 | /* r/r+ and buf: read at beginning, full size available. */ |
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| 327 | c->pos = c->append = 0; |
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| 328 | c->eof = size; |
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| 329 | break; |
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| 330 | case 'w': |
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| 331 | /* w/w+ and buf: write at beginning, truncate to empty. */ |
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| 332 | c->pos = c->append = c->eof = 0; |
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| 333 | *c->buf = '\0'; |
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| 334 | break; |
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| 335 | default: |
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| 336 | abort (); |
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| 337 | } |
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| 338 | } |
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| 339 | |
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| 340 | _newlib_flockfile_start (fp); |
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| 341 | fp->_file = -1; |
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| 342 | fp->_flags = flags; |
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| 343 | fp->_cookie = c; |
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| 344 | fp->_read = flags & (__SRD | __SRW) ? fmemreader : NULL; |
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| 345 | fp->_write = flags & (__SWR | __SRW) ? fmemwriter : NULL; |
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| 346 | fp->_seek = fmemseeker; |
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| 347 | #ifdef __LARGE64_FILES |
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| 348 | fp->_seek64 = fmemseeker64; |
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| 349 | fp->_flags |= __SL64; |
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| 350 | #endif |
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| 351 | fp->_close = fmemcloser; |
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| 352 | _newlib_flockfile_end (fp); |
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| 353 | return fp; |
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| 354 | } |
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| 355 | |
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| 356 | #ifndef _REENT_ONLY |
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| 357 | FILE * |
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| 358 | fmemopen (void *__restrict buf, |
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| 359 | size_t size, |
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| 360 | const char *__restrict mode) |
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| 361 | { |
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| 362 | return _fmemopen_r (_REENT, buf, size, mode); |
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| 363 | } |
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| 364 | #endif /* !_REENT_ONLY */ |
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