C++ string Class 使用

C++ string class

The C++ Standard Template Library (STL) contains a string class that is used in several computer science classes. In order to use the string class you should include the following statements:
#include <string>
using std::string;

The following examples assume these declarations and initial values for each:

string s = "abc def abc";
string s2 = "abcde uvwxyz";
char c;
char ch[] = "aba daba do";
char *cp = ch;
unsigned int i;

Stream input cin >> s; Changes the value of s to the value read in. The value stops at whitespace. Stream output cout << s; Writes the string to the specified output stream. Line input getline(cin, s); Reads everything up to the next newline character and puts the result into the specified string variable. Assignment s = s2;s = "abc";
s = ch; s = cp; A string literal or a string variable or a character array can be assigned to a string variable. The last two assignments have the same effect. Subscript s[1] = 'c';
c = s[1]; Changes s to equal "acc def abc"
Sets c to 'b'. The subscript operator returns a char value, not a string value. Length i = s.length();
i = s.size(); Either example sets i to the current length of the string s Empty? if(s.empty()) i++;
if(s == "") i++; Both examples add 1 to i if string s is now empty Relational operators if (s < s2) i++; Uses ASCII code to determine which string is smaller. Here the condition is true because a space comes before letter d Concatenation

s2 = s2 + "x";
s2 += "x";

Both examples add x to the end of s2 Substring

s = s2.substr(1,4);
s = s2.substr(1,50);

The first example starts in position 1 of s2 and takes 4 characters, setting s to "bcde". In the second example, s is set to "bcde uvwxyz". If the length specified is longer than the remaining number of characters, the rest of the string is used. The first position in a string is position 0. Substring replace s.replace(4,3,"x"); Replaces the three characters of s beginning in position 4 with the character x. Variable s is set to "abc x abc". Substring removal s.erase(4,5);
s.erase(4); Removes the five characters starting in position 4 of s. The new value of s is "abc bc".
Remove from position 4 to end of string. The new value of s is "abc ". Character array to string s = ch; Converts character array ch into string s. String to character array cp = s.c_str(); Pointer cp points to a character array with the same characters as s. Pattern matching

i = s.find("ab",4);

if(s.rfind("ab",4) != string::npos)
   cout << "Yes" << endl;

The first example returns the position of the substring "ab" starting the search in position 4. Sets i to 8. The find and rfind functions return the unsigned int string::npos if substring not found. The second example searches from right to left starting at position 4. Since the substring is found, the word Yes is printed.

Because of a bug in the bgunix version of the g++ compiler, writing a string variable under setw control doesn't work. You need to use the c_str member function, like this:
cout << setw(15) << s.c_str() << endl;