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Character processing

Character Processing

Topics

• Character type.

• Character constants.

• Character variables.

• Character manipulation.

Character type

Single characters and strings

• Single characters.

• Strings of characters.
  • Character strings have a length.

  • Characters within a string are referred to by position:
    
    

Character Constants

• Either single quotes `...' or double quotes "..."

• Character constants are most often used to enhance I/O:

  WRITE(6,*) `Enter value for radius`

  READ(5,*) radius

  area = pi*radius*radius

  WRITE(6,*) `Area of circle r=', &

  radius, ` is `, area

  Which appears on screen as:

  Enter value for radius

  12.0

  Area of circle r= 12.0 is 452.38925

• If the string contains a type of delimiter:
  • use the other to enclose the string, for example:

`This " is a double quote'

• To consistently use one delimiter it may be included in string as a double character, for example:

Character Variables

Specification

• Single characters:

• Strings:
  • maximum length for the string is specified using len=

CHARACTER(len=6) :: initials, title

title = `Prof.'

initials = `FJS'

surname = `Bloggs'

• General form:

Character manipulation

Concatenation

• Strings may be concatenated as follows:

CHARACTER (len=24) :: name

surname = `Bloggs'

name = `Dr `//`Fred `//surname

• Truncation and padding for strings of different lengths:
  • if the right hand side is shorter the result is truncated.

  • if the left hand string is shorter - the result is padded with blanks.

Substrings

• Selected by position with respect to the leftmost character:

• For example.

lang(2:4) !ort

lang(6:6) !a

lang(:4) !Fort

lang(6:) !an

lang(:) !Fortran

lang(10:) !zero length string.

lang(5:10) !illegal 10>len

Intrinsic functions

• Intrinsic function, example:
  • LEN(string) - returns string length.

  • INDEX(sub,string) - returns the position of string within string, or 0.

  • TRIM(string) - returns the string without trailing blanks.

• Example:

INTEGER :: length, pos

...

length = LEN(surname) !len=12

firstname = `Walter`

pos = INDEX(firstname, `al`) !pos=2

firstname = `Fred`

pos = INDEX(firstname, `al`) !pos=0

length = LEN(TRIM(firstname)) !len=4