软件设计（II）教学课件：Chapter15 String.ppt

Chapter 15 String
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The C++ “string” Class
A C++ library class defined in <string>
With more features than C-string functions
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Constructing a String
A string object with empty string:
string newString;
A string object from a string literal or an char array:

string newString(stringLiteral);
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Appending a String
string s1("Welcome");
(" to C++"); // appends " to C++" to s1
cout << s1 << endl; //Welcome to C++
string s2("Welcome");
(" to C and C++", 0, 5);
cout << s2 << endl; //Welcome C an
string s3("Welcome");
(" to C and C++", 5);
cout << s3 << endl; //Welcome to C
string s4("Welcome");
(4, 'G');
cout << s4 << endl; //WelcomeGGGG
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Assigning a String
You can use several overloaded functions to assign new contents to a string. For example, see the following code:
string s1("Welcome");
("Dallas"); // assigns "Dallas" to s1
cout << s1 << endl; // s1 now becomes Dallas
string s2("Welcome");
("Dallas, Texas", 0, 5); // assigns "Dalla" to s2
cout << s2 << endl; // s2 now becomes Dalla
string s3("Welcome");
("Dallas, Texas", 5); // assigns "Dalla" to s3
cout << s3 << endl; // s3 now becomes Dalla
string s4("Welcome");
(4, 'G'); // assigns "GGGG" to s4
cout << s4 << endl; // s4 now becomes GGGG
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Functions at, clear, erase, and empty
You can use the at(index) function to retrieve a character at a specified index, clear() to clear the string, erase(index, n) to delete part of the string, and empty() to test if a string is empty. For example, see the following code:
string s1("Welcome");
cout << (3) << endl; // (3) returns c
cout << (2, 3) << endl; // s1 is now Weme
(); // s1 is now empty
cout << () << endl; // returns 1 (means true)
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Comparing Strings
Often, in a program, you need to compare the contents of two strings. You can use the compare function. This function works in the same way as the C-string s