CPS120: Introduction to Computer Science

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CPS120 Introduction to Computer Science

• Using a String Class

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C Includes vs C Inclues

• Header file names no longer maintain the .h
  extension as in the case of stdio.h, stdlib.h,
  iostream.h, etc. This extension h simply
  disappears and iostream.h becomes iostream
  (without .h).
• All classes and functions defined in standard
  libraries are under the std namespace instead of
  being global. This not applies to C macros that
  remain as C macros

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Proper form for C

• include lt iostream gt
• include lt string gt
• using namespace std

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Use ltstringgt instead of ltstring.hgt

• ltstring.hgt is the standard C library for
  manipulating C strings, i.e. arrays of char
  terminated with a 0.
• The string class library header is supposed to be
  called string too. The Standard says that C
  standard header files, such as the string class
  uses, are referenced without the .h extension,
  which is reserved for backward compatibility with
  older C libraries.

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Using C-Type Strings
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Strings

• No native STRING type
• Use null-character terminated arrays
• Strings are handled fundamentally differently
• Assigning You can hardly ever use the ""
• Need to use strcpy(string1, string2)
• Comparing
• Calculating length

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string.h

• Gives access to functions for handling strings
  like
• strlen( )
• strcat( )
• strcmp( )
• strcpy( )

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Concatenation

• The STRCAT function will continue to add
  characters even if it reaches the end of the
  destination character array
• The result is that other memory is overwritten
• with the remaining string data.

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Converting Strings

• There are C library functions that allow you to
  conver4t numbers stored in strings to integer and
  floating point values.

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Using a String Class

• Using the features of C

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String Classes

• Strings in C are objects
• There are member functions associated with every
  object of the type string.
• length( )
• stringQ.length ( )
• The dot indicates the operation is being invoked
  on the object to the left of the dot
• The string class seems more like other native
  data types
• Strings can be assigned with ""
• Stings can be added together

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A String Class

• A string class can make C strings much easier
  to use
• a) A string class can provide bounds checking to
  avoid string errors
• b) A string class can also allow the use of
  standard C operators when working with strings
• i) , , and

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A Brave New World

• include ltiostreamgt
• include ltstringgt
• using namespace std
• int main ( )
• string Greeting
• Greeting "Hello World!"
• cout ltlt Greeting ltlt endl
• return 0

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Library functions manipulate strings

• length function
• stringLength userString.length( )
• To compare two strings
• if (string1 string2)
• Test two strings alphabetically
• if (string1 lt string2)
• cout ltlt "string1 comes before string2
• alphabetically "

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Obtaining Length

• Obtain length
• Length MyString2.length()

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Assigning Values to Strings

• MyString1 MyString2
• MyString1 "string variable"
• MyString1 'A'

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Indexing Characters

• Indexing characters to a string object
• MyString10 'B'

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Comparisons

• Using a string class you can directly compare two
  strings
• Previously you had to call a special function
  strcmp( )

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Substrings

• Most languages have an operation for extracting
  part of a string
• In C, you supply the starting position and the
  number of characters to extract
• substr member function (operator)
• stringA.substr(start, len)

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Searching and String Classes

• Find the First Occurrence of One String Within
  Another
• Location MyString2.find("Wor")
• Returns a position or 1 if not found
• Find First Occurrence of a Character Within a
  String
• Location MyString2.find('W')
• Returns a position or 1 if not found
• Returning a substring of Characters from the
  string
• MyString1 MyString2.substr(0,5)

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In Conclusion

• You can continue to use both old and new style
  strings in the same program
• Requires both a string and a string.h include