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C++ STRINGS

C++ STRINGS. string is part of the Standard C++ Library new stuff: cin : standard input stream (normally the keyboard) of type istream. >> operator string constructor (#, character) + concatenation operator on strings size member function. #include <string>.

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C++ STRINGS

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  1. C++ STRINGS • string is part of the Standard C++ Library • new stuff: • cin : standard input stream (normally the keyboard) of type istream. • >> operator • string constructor (#, character) • + concatenation operator on strings • size member function

  2. #include <string> • Provides access to the standard string library. • Look in includes for reference • on esus: /usr/include/cxx • on linux: /usr/include/g++-3 (my 7.1 RedHat) • A better way to look up the standard library is in a reference book such as "The C++ Standard Library, A Tutorial and Reference" by Nicolai M. Josuttis Addision/Wesley, 1999 ISBN - 0-201-37926-0

  3. string name; • Instantiates a local variable (named object) of type string. Can be anywhere before it's used. • Gains access to the interface, (the member functions (methods) or operations of the string type. • This definition uses the default constructor and generates a null string. • Scope is only for this function (main) and is destroyed when leaving the scope.

  4. cin >> name; • Read from the standard input into the data area of name. • First it skips any whitespace characters (space, tab, backspace, or end of the line). • Next it reads any characters into name until it encounters another whitespace character or end-of-file. • The value of the expression is cin. • Tries to flush properly to display previous couts.

  5. const string greeting = "Hello, " + name + "!"; • const promises that we will never change this variable again. • const definitions MUST be initialized when defined. • This definition can use the values of previous variables as it does here. • + is a concatenation operator within the string object. ("x"+name, name+"x", name+name, but NOT "x"+"x"); • Example of overloading the + operator.

  6. const string spaces(greeting.size(), ' '); • Another instantiation of a object of type string. • This object is called spaces. • In this example, a different constructor is called. • (num, character) returns num characters. • greeting.size() is a member function of the greeting object which returns an integer number for the length of the string stored in greeting. • Result is a set of spaces the same size as greeting.

  7. CHARACTER LITERALS • In the previous constructor (num character) we used the character literal ' ' for a single character that is a blank. • Distinct from the string literal " ". • The type of ' ' is char. • The type of " " is an array of const char with one more element than the number of characters in the literal (the '\0' null character).

  8. DETAILS • char : built-in type that holds ordinary characters defined by the implementation. • wchar_t: built-in type that holds "wide characters" which are big enough to hold characters for languages such as Japanese. • Review other examples of constructors and other member functions on page 15.

  9. STRING CONSTRUCTORS • string s; creates the empty string s • string s(str); creates a string as a copy of the existing string str. • string s(str, stridx); creates a string s that is initialized by the characters of string str starting with index stridx. • string(str, stridx, strlen); creates a string s that is initialized by, at most, strlen characters of string str starting with index stridx.

  10. STRING CONSTRUCTORS(cont.) • string s(cstr); creates a string s that is initialized by the C-string cstr. • string s(chars, chars_len); creates a string s that is initialized by chars_len characters of the character array chars. • string s(num c); creates a string that has num occurrences of character c. • string s(beg,end); creates a string that is initialized by all characters of the range [beg,end].

  11. STRING DESTRUCTOR • s.~string(); destroys all characters and frees the memory.

  12. STRING MEMBER FUNCTIONS(METHODS) • =,assign() Assign a new value • swap() Swaps values between two strings • +=, append(), push_back() Appends characters • insert() Inserts characters • erase() Erase characters • clear() Remove all characters (makes it empty) • resize() Changes the number of characters (deletes or appends characters at the end)

  13. STRING MEMBER FUNCTIONS(cont.) • replace() Replaces characters • + Concatenates strings • ==, !=, <, <=, >, >=, compare() Compare strings • size(), length() Return the number of characters • max_size() Returns the maximum possible number of characters • empty() Returns whether the string is empty • capacity() Returns the number of characters that can be held without reallocation.

  14. STRING MEMBER FUNCTIONS(cont.) • reserve() Reserves memory for a certain number of characters • [], at() Access a character • >>, getline() Read the value from a stream • << Writes the value to a stream • copy() Copies or writes the contents to a C-string • c_str() Returns the value as C-string

  15. STRING MEMBER FUNCTIONS(cont.) • data() Returns the value as character array • substr() Returns a certain substring • find functions Search for a certain substring or character • begin(), end() Provide normal iterator support • rbegin(), rend() Provide reverse iterator support • get_allocator() Returns the allocator

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