From Cppreference
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FILE *fopen( const char *filename, const char *mode, FILE *stream );
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Reassigns an existing file stream stream to a different file identified by filenameusing specified mode. mode is used to determine the new file access mode.
[edit] Parameters
filename
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-
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file name to associate the file stream to
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mode
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-
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null-terminated character string determining new file access mode
File access mode string
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Meaning
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Explanation
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Action if file already exists
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Action if file does not exist
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"r"
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read
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Open a file for reading
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read from start
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failure to open
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"w"
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write
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Create a file for writing
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destroy contents
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create new
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"a"
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append
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Append to a file
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write to end
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create new
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"r+"
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read extended
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Open a file for read/write
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read from start
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error
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"w+"
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write extended
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Create a file for read/write
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destroy contents
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create new
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"a+"
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append extended
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Open a file for read/write
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write to end
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create new
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File access mode flag "b" can optionally be specified to open a file in binary mode. This flag has effect only on Windows systems. On the append file access modes, data is written to the end of the file regardless of the current position of the file position indicator.
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stream
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the file stream to modify
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[edit] Return value
stream on success, NULL on failure
[edit] See also
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opens a file (function)
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closes a file (function)
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