FILES

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FILES

• 10.2

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FILES IN C

• A file is viewed as a stream
• of bytes by a C program.
• Any structure put on a file
• is put there by the programmer

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FILE

• A file is a structure
• in which C keeps
• information about a file.

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3 Files are opened

• When a C program is executed
• 3 Files are automatically opened
• 1. Standard input (stdin)
• which is usually input from the keyboard
• 2. Standard output (stdout)
• which is usually output to the terminal
• 3. Standard error (stderr)
• which is usually terminal output

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stdio.h

• The identifier FILE
• is declared in the file
• stdio.h
• with a typedef declaration

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stdio.h

• The header file
• stdio.h
• must be included in programs
• using external files

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FILE

• When an external file
• is to be opened
• for use in a program
• the programmer must declare
• a new variable of type FILE
• FILE infile, outfile

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fopen ( )

• Makes a file available for use
• by the program.
• After the declaration, infile and outfile
• the file needs to be connected with the file on
  the disk
• Infile fopen ( fname, r )

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File Modes

• r open an existing file for reading only
• w open a new file for writing only
• a open a file for appending
• (writing at the end of the file)
• r open an existing file for update
• (reading and writing)
• w open (create) a new file for update
• a open a (new or existing) file for
• reading and appending

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fclose ( )

• At the end of a program execution,
• the connection between the file
• and the program should be broken.
• This is done by closing the file
• with the C library function
• fclose ( ).
• Example
• fclose ( infile )

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fclose

• The parameter fclose ( )
• is the FILE variable that references
• the file to close.
• The function fclose ( ) returns an integer.

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Error Handling with fopen ( ) and fclose ( )

• These library functions have facilities
• to report errors
• when they occur
• while opening or closing a file

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fopen - Error Handling

• No error - returns pointer to FILE structure
• error - NULL pointer returned

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fclose - Error Handling

• No Error - 0 returned (closed successful)
• Error - EOF returned

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Random versus Sequential Access in Files (10.7)

• Sequential X------------gt
• opened
• reading or writing starts at beginning
• pointer proceeds through
• to end of file

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RANDOM ACCESS

• Reading of the records in any order
• 3 ----gt 15 ----gt 1
• fseek ( ) moves filepointer to byte position
• fseek (fp, offset, start)

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RANDOM ACCESS

• ftell ( ) returns current byte offset from the
  beginning of the file
• fseek (fp, (long) 0 , 0 )

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Close Look at stdio.h (10.8)

• Contains facilities for input and output
• This file differs for each computer systems
  because the input and output library functions
  are different.

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A file contains at least 3 members

• 1. A member that counts the number of characters
  still to be processed before the buffer needs to
  be refreshed.

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A file contains at least 3 members

• 2. The address of the Buffer

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A file contains at least 3 members

• 3. The pointer into the current position in the
  buffer

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Preprocessor-defined constants in stdio.h

• define
• EOF
• NULL
• BUFSIZ size of default buffer

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Typedef declaration

• Typedef struct
• short count
• number of unprocessed characters
• cells in the buffer
• char bufaddr
• the address of the buffer
• char curptr
• pointer to the current position of the buffer

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Things to Remember

• 1. Input and output may be either buffered or
  line buffered.
• 2. A file is a stream of bytes to a C program.
  Any structure put on a file is put there by the
  programmer.
• 3. When a C program is executed, three files are
  automatically opened standard input, output and
  error.

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Things to Remember

• 4. The return value from a call to a library
  function usually indicates when an error had
  occurred.
• 5. The utilities getc() and getchar() return a
  value of type int. Using type char will, at best,
  produce nonportable code.
• 6. A FILE is a structure that C uses to keep
  track of the current position in a file. One FILE
  structure is kept up to date for every open file
  in the program.

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Review Exam 3

• Input and Output C 10.1 10.6
• Files C 10.2, 10.7, 10.8
• Group Project
• Windows Programming

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Group Project Proposal due this Friday

• Format Power Point Presentation
• Submit Floppy Disk Hard Copy
• Present In Class
• Who Involve all group members
• Length 5 minutes
• Dress Informal / Formal optional