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.

Department of Computer Science

Dr. Jong Kwan "Jake" Lee, Chair
Department of Computer Science
Bowling Green State University
Bowling Green, OH 43403
leej@bgsu.edu

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Updated: 07/09/2018 01:38PM