1FOPEN(3)                   Linux Programmer's Manual                  FOPEN(3)
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NAME

6       fopen, fdopen, freopen - stream open functions
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SYNOPSIS

9       #include <stdio.h>
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11       FILE *fopen(const char *pathname, const char *mode);
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13       FILE *fdopen(int fd, const char *mode);
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15       FILE *freopen(const char *pathname, const char *mode, FILE *stream);
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17   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
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19       fdopen(): _POSIX_C_SOURCE
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DESCRIPTION

22       The fopen() function opens the file whose name is the string pointed to
23       by pathname and associates a stream with it.
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25       The argument mode points to a string beginning with one of the  follow‐
26       ing sequences (possibly followed by additional characters, as described
27       below):
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29       r      Open text file for reading.  The stream  is  positioned  at  the
30              beginning of the file.
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32       r+     Open  for  reading and writing.  The stream is positioned at the
33              beginning of the file.
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35       w      Truncate file to zero length or create text  file  for  writing.
36              The stream is positioned at the beginning of the file.
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38       w+     Open  for  reading  and writing.  The file is created if it does
39              not exist, otherwise it is truncated.  The stream is  positioned
40              at the beginning of the file.
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42       a      Open  for  appending (writing at end of file).  The file is cre‐
43              ated if it does not exist.  The stream is positioned at the  end
44              of the file.
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46       a+     Open  for  reading  and appending (writing at end of file).  The
47              file is created if it does not exist.  The initial file position
48              for  reading  is  at  the  beginning  of the file, but output is
49              always appended to the end of the file.
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51       The mode string can also include the letter 'b' either as a last  char‐
52       acter  or as a character between the characters in any of the two-char‐
53       acter strings described above.  This is strictly for compatibility with
54       C89  and has no effect; the 'b' is ignored on all POSIX conforming sys‐
55       tems, including Linux.  (Other systems may treat text files and  binary
56       files  differently, and adding the 'b' may be a good idea if you do I/O
57       to a binary file and expect that your program may be ported to non-UNIX
58       environments.)
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60       See NOTES below for details of glibc extensions for mode.
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62       Any  created  file  will  have  the  mode S_IRUSR | S_IWUSR | S_IRGRP |
63       S_IWGRP | S_IROTH | S_IWOTH (0666), as modified by the process's  umask
64       value (see umask(2)).
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66       Reads  and writes may be intermixed on read/write streams in any order.
67       Note that ANSI C requires that a file  positioning  function  intervene
68       between  output and input, unless an input operation encounters end-of-
69       file.  (If this condition is not met, then a read is allowed to  return
70       the result of writes other than the most recent.)  Therefore it is good
71       practice (and  indeed  sometimes  necessary  under  Linux)  to  put  an
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