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:
| 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. |
