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─────Run-Time Library───────────────────────────────────────────────────────
 
  Constant:  "a", "a+", "r", "r+", "w", "w+"
 
  Include:   <stdio.h>
 
  Context:   _fdopen, fopen, freopen, _fsopen, _fwopen
 
  Summary:   Specifies the access type ("a", "r", or "w") requested
             for the file. Both the translation mode ("b" or "t") and
             the commit-to-disk mode ("c" or "n") can be specified with
             the type of access.
 
     The access types are described below.
 
     Type     Description
 
     "a"      Opens for writing at the end of the file (appending);
              creates the file first if it does not exist. All write
              operations occur at the end of the file. Although the
              file pointer can be repositioned using fseek or rewind,
              it is always moved back to the end of the file before
              any write operation is carried out.
 
     "a"      Same as above, but also allows reading.
 
     "r"      Opens for reading. If the file does not exist or cannot
              be found, the call to open the file will fail.
 
     "r+"     Opens for both reading and writing. If the file does not
              exist, or cannot be found, the call to open the file
              will fail.
 
     "w"      Opens an empty file for writing. If the given file
              exists, its contents are destroyed.
 
     "w+"     Opens an empty file for both reading and writing. If the
              given file exists, its contents are destroyed.
 
     When the "r+", "w+", or "a+" type is specified, both reading and
     writing are allowed (the file is said to be open for update).
     However, when switching between reading and writing, you must
     reposition the file pointer, using fsetpos, fseek, or rewind. You
     can specify the current position, if desired.
                                    -♦-