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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.