Strings in C

1
Strings in C

2
To use "new" strings in C

• to use string CONSTANTS in double quotes, just
  use them - no library needed
• to use string variables and functions, you must
  include ltstringgt
• declare string variables
• assignment statement
• input with extraction operator
• output with insertion operator

3
String Operators and Methods

• concatenation
• dot notation
• length()
• substr()
• find()

4
concatenation

• operator is
• at least one of the two operands must be a string
  variable
• example call if name Bob, expression
• name "by Roberts" results in one string
  "Bobby Roberts"
• does not automatically put spaces in

5
length method

• Function length returns an unsigned integer value
  that equals the number of characters currently in
  the string
• Function size returns the same value as function
  length
• You must use dot notation in the call to function
  length or size

6
length method

• no arguments, just ()
• smallest return possible is 0 (empty string)
• treat return type as an integer
• word Johnson
• x word.length() // gives x value 7

7
substr method

• two arguments usually
• example call name.substr(4, 3)
• first argument is position to start the string
• Positions of characters within a string are
  numbered starting from 0, not 1
• second argument is how many characters
• if second argument is omitted, means "until end
  of string"
• returns a string (NOT a character)

8
find method

• one argument
• example call name.find("Andy")
• argument can be string or character
• finds FIRST one from the left
• case matters!
• returns integer (actually size_t)
• returns leftmost position found
• or stringnpos if not found

9
find method

• Function find returns an unsigned integer value
  that is the beginning position for the first
  occurrence of a particular substring within the
  string
• The substring argument can be a string constant,
  a string expression, or a char value
• If the substring was not found, function find
  returns the special value stringnpos

10
String Methods - Examples

• string street "123 Main Street"
• string number, st // declarations
• int stlen, space_pos, x_pos
• stlen street.length() // 15
• space_pos street.find (" ") // 3
• x_pos street.find ("x") // npos
• number street.substr(0,3) // "123"
• st street.substr(9) // "Street"

11
Subscript notation

• Another way to access individual elements of a
  string is with a subscript
• If word joe, then word0 is j
• A character, not a smaller string
• word1 is o and word2 is e
• Be very careful about assigning string elements
  values like this sometimes the length field is
  not correctly updated