Data Structures in C

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Data Structures in C

• struct and typedef

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struct

• Allows you to define a data structure composed of
  pre-defined types.
• struct may include other structures.
• structs may refer to themselves.
• struct defines a template for the data structure.

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Using Structs

• Structs are generally globally defined. (Before
  the main function.)
• Syntax
• struct ltnamegt
• ltdatatypegt ltnamegt
• ltdatatypegt ltnamegt

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Declaring Variables with Struct

• Variables follow normal naming rules.
• A struct is not recognized as a data type by
  default.
• Structs may be made into datatypes using the
  typedef statement.

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Declaring Variables with struct.

• struct record
• char name40
• int age
• void main(void)
• struct record rec
• struct record recref
• printf(Name s, Age d\n, rec.name, rec.age)
• printf(Names, Age d\n, recref-gtname,
  recref-gtage)

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typedef

• Adds a synonym for a data type.
• typedef struct
• char name40
• int age
• record
• Defines a synonym record for the structure.
• This allows you to define code like.
• record rec
• Which will allocate space for a record structure
  named rec.
• typedef may also be used to rename internal data
  types.

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typedef(cont.)

• To rename a datatype.
• typedef ltdatatypegt ltnewnamegt
• If color is represented by an integer value it
  might be useful to define
• typedef int color

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File Handling

• All file handling is based on the FILE
  datatype.
• FILE is referred to a a file pointer.
• FILE associates the information in a file with
  the data on disk.
• To get a file pointer you must first open the
  file.
• The fopen function returns a FILE for use in
  your program.

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fopen()

• Syntax
• void main(void)
• FILE fp
• fp fopen( filename.ext, r)
• // Make sure to close your file after processing
• fclose(fp)

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File handling

• FILE fopen( char ltnamegt,char mode)
• name is a string containing the name of the file
• mode is a string containing one of the following
• r - file is opened to read file must exist.
• w file is opened for writing file destroyed.
• r file is opened for read and write file
  must exist
• w file opened for read and write file
  destroyed.
• u file opened for update file may be read
  writing occurs at the end of the file.

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File handling continued.

• In addition to these modes a file may be opened
  either as a binary or text file.
• Text files may only contain ASCII data.
• Binary files contain images of the data.
• Files are opened as text by adding a t to the
  open mode.
• Files are opened as binary by adding a b to the
  open mode.

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File handling continued again

• Once the file is opened you need to read from it
  or write to it.
• We can use formatted input and output for this
  purpose.
• Standard output file stdout
• printf( char format, var, ,varn)
• Standard input file stdin
• scanf( char format, var, ,varn)

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File handling yet again(so little hope for
advancement )

• Functions to deal with specific files.
• fscanf( FILE , char format, var, , varn)
• fprintf( FILE , char format, var, , varn)

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File handling yet again(so little hope for
advancement )

• Another way to read and write files.
• fread() and fwrite()
• fread( void buffer,int size, int count, FILE
  )
• fwrite( void buffer, int size, int count, FILE
  )
• Use sizeof() to calculate size.
• Usually use 1 for the count unless you have a
  specific need.

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