The string library

When discussing common data types we briefly mentioned the type string. What sets this data type apart from the other common types (e.g. int, double, char) is that the string type is not a part of the language's core (i.e, not a "primitive" data type).

Instead it is an example of a class which happens to have been defined in one of the standard C++ libraries. Therefore, when we wish to use it we must preface our code with the directive:

#include <string>

Let me stress that these notes are meant as a very coarse outline; please refer to the text for more explanation.

A string object has a set of attributes or data members (for representing the state of the object), yet it also supports a set of actions or member functions. We will look at several examples of the actions supported by this class. For each, we will focus on the transfer of information which takes places in such a method call, namely in the parameters sent to the method, and in the return value sent back as a result.

• int size()
  returns the total length of the string

• char at(int index)
  returns the single character at the given index

• substr(int start, int length)
  returns a substring starting at index 'start' and going for up to length characters.

• int find(string pattern)
  int find(string pattern, int start) returns the smallest index >= start, if one exists, such that the given pattern can be found as a substring in the original string starting at such index.

Several operators have been defined to deal with string data as well, most notably:

• The << operator for printing a string

  cout << firstName;

• The >> operator for inputting a string

  cin >> lastName;

• The + operator for concatenating two or more strings

  fullName = firstName + " " + lastName;

A further note about reading strings from input. When using the >> operator, such as in

cin >> name;

Saint Louis University

getline(istream streamName, string result)
getline(istream streamName, string result, char delim)