CPS 125: Digital Computation and Programming

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CPS 125 Digital Computation and Programming

• Text and Binary File Processing

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Outline

• Input/Output Files
• Binary Files
• Search a Database
• Case Study
• Common Programming Errors

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Files

• Any collection of information stored in the
  computers secondary storage
• Has a name, usually divided into two parts
• filename.ext
• Certain extensions have predefined meanings
• c - C source lib - library file exe -
  Program txt - text file

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Text Files

• A named collection of characters saved in
  secondary storage
• It appears as two-dimensional (line by line), but
  actually it is stored as a one-dimensional
  sequence of chars
• Special printing characters
• New line character \n
• End-of-file character EOF (normally as a negative
  number returned from scanf function, have to
  catch it to stop reading the file)

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String vs. Text File

• String Text File
• sequence of characters sequence of characters
• usually short usually long
• ends with null character ends with EOF character
• temporary in memory permanent on disk
• direct access si sequential access

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Escape Sequences

• \n new line
• \t tab
• \f form feed (new page)
• \r return (go back to column 1 of current
  output line)
• \b backspace
• \\ the actual backslash \

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Formatting Output with printf

• c a single character
• s a string
• d an integer (base 10)
• o an integer (base 8)
• x an integer (base 16)
• f a floating-point number
• e a floating-point number in scientific notation
• E a floating-point number in scientific notation
• a sign

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Using Files in C

• Operations in ltstdio.hgt
• Steps
• Declare variable of type FILE
• Open file using fopen
• Perform I/O using functions in ltstdio.hgt
• Close file using fclose

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FILE Pointer

• C Standard type FILE avoids system differences in
  file systems
• Must declare separate variable for each file that
  is open simultaneously
• For example, for input and output, use
• FILE infp, outfp
• Functions for input will use infp as argument,
  those for output will use outfp

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Opening a File

• Opening a file means associating the FILE
  variable with an actual file on disk
• Use call of form
• file-pointer fopen(filename, mode)
• If the call unsuccessful, return NULL
• if (file-pointer NULL) /handle error/
• printf(Cannot open file \n)
• The mode specifies type of data transfer
• r - read w - write a - append

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File Modes

• r - open for reading (input operations) -
  file must already exist
• w - open for writing (output operations) -
  new file created (erases old one)
• a - open for appending (output operations) -
  new file created if none already exists - info
  put at end of existing file otherwise

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Performing I/O Operations

• Character by character
• getc and putc
• Line by line
• fgets and fputs
• Formatted data
• fscanf and fprintf

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Closing Files

• Be sure to close files when finished with them
• Helps prevent errors, and having too many files
  open at once
• Exiting from program closes files, but avoid it
• Use
• fclose(infp)
• fclose(outfp)

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Standard Files

• The standard I/O library defines three special
  identifiers as FILE constants
• stdin - standard input file (usually keyboard)
• stdout - standard output file (usually screen)
• stderr - standard error file for error
  messages (usually screen)

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scanf use

• scanf returns the number of values correctly
  converted, or EOF if at the end-of-file marker
• Each argument after the format string must be a
  pointer
• For simple variables, use for address
• For arrays, name is automatically a pointer
• scanf(d s, num, name)

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Binary Files

• A file containing binary numbers that are the
  computers internal representation
• FILE bi_fp
• int i
• bi_fp fopen("nums.bin", "wb")
• for (i 2 i lt 500 i 2)
• fwrite(i, sizeof (int), 1, bi_fp)
• fclose(bi_fp)
• If array score is an array of 10 integers,
• fwrite(score, sizeof(int), 10, binaryp)
  
• fread has the same form (arguments) as fwrite