Learn C++ - C++ String Class

C++ has a string class.

You can use a type string variable.

To use the string class, a program has to include the string header file.

The string class is part of the std namespace.

The class lets you treat a string much like an ordinary variable.

Example

The following code illustrates some of the similarities and differences between string objects and character arrays.


#include <iostream> 
#include <string>               // make string class available 
using namespace std; 
int main() { //from  w  w  w  .j a va 2 s.  c  o  m
    char my_char1[20];            // create an empty array 
    char my_char2[20] = "C++"; // create an initialized array 
    string str1;                // create an empty string object 
    string str2 = "Java";    // create an initialized string 

    cout << "Enter a string: "; 
    cin >> my_char1; 
    cout << "Enter another string: "; 
    cin >> str1;                // use cin for input 
    cout << my_char1 << " " << my_char2 << " " 
          << str1 << " " << str2 // use cout for output 
          << endl; 
    cout << "The third letter in " << my_char2 << " is " 
          << my_char2[2] << endl; 
    cout << "The third letter in " << str2 << " is " 
          << str2[2] << endl;    // use array notation 

    return 0; 
}

The code above generates the following result.

Example 2

The following code shows some String usages.

Note that you can add and append C-style strings as well as string objects to a string object.


#include <iostream> 
#include <string>               // make string class available 
using namespace std; 
int main() { /*from  www  .  ja  v  a  2  s.c  o  m*/
    string s1 = "java2s.com"; 
    string s2, s3; 

    cout << "You can assign one string object to another: s2 = s1\n"; 
    s2 = s1; 
    cout << "s1: " << s1 << ", s2: " << s2 << endl; 
    cout << "You can assign a C-style string to a string object.\n"; 
    cout << "s2 = \"new Value\"\n"; 
    s2 = "C++"; 
    cout << "s2: " << s2 << endl; 
    cout << "You can concatenate strings: s3 = s1 + s2\n"; 
    s3 = s1 + s2; 
    cout << "s3: " << s3 << endl; 
    cout << "You can append strings.\n"; 
    s1 += s2; 
    cout <<"s1 += s2 yields s1 = " << s1 << endl; 
    s2 += " for a day"; 
    cout <<"s2 += \" for a day\" yields s2 = " << s2 << endl; 

    return 0; 
}

The code above generates the following result.

Example 3

C library equivalent of

str3 = str1 + str2;

is this:

strcpy(my_char3, my_char1); 
strcat(my_char3, my_char2);

The following code compares techniques used with string objects with techniques used with character arrays.


#include <iostream> 
#include <string>               // make string class available 
#include <cstring>              // C-style string library 
using namespace std; 
int main() { /*from   ww w  .  ja va  2  s  .c  om*/
     char my_char1[20]; 
     char my_char2[20] = "java2s.com"; 
     string str1; 
     string str2 = "C++"; 

     str1 = str2;                // copy str2 to str1 
     strcpy(my_char1, my_char2); // copy my_char2 to my_char1 

     str1 += " vs ";              // add to the end of str1 
     strcat(my_char1, " Java");   // add to the end of my_char1 

     int len1 = str1.size();     // obtain length of str1 
     int len2 = strlen(my_char1);// obtain length of my_char1 

     cout << "The string " << str1 << " contains " 
           << len1 << " characters.\n"; 
     cout << "The string " << my_char1 << " contains " 
           << len2 << " characters.\n"; 

     return 0; 
}

The code above generates the following result.

string Class I/O

You can use cin with the >> operator to read a string object and cout with the << operator to display a string object using the same syntax you use with a C-style string.

Reading a line at a time instead of a word at time uses a different syntax.


#include <iostream> 
#include <string>               // make string class available 
#include <cstring>              // C-style string library 
using namespace std; 
int main() { /*from  ww w  . j  av a  2 s. c om*/
     char my_char[20]; 
     string str; 

     cout << "Length of string: " 
          << strlen(my_char) << endl; 
     cout << "Length of string in str before input: " 
          << str.size() << endl; 
     cout << "Enter a line of text:\n"; 
     cin.getline(my_char, 20);     // indicate maximum length 
     cout << "You entered: " << my_char << endl; 
     cout << "Enter another line of text:\n"; 
     getline(cin, str);          // cin now an argument; no length specifier 
     cout << "You entered: " << str << endl; 
     cout << "Length of string in my_char after input: " 
          << strlen(my_char) << endl; 
     cout << "Length of string in str after input: " 
          << str.size() << endl; 
     return 0; 
}

The code above generates the following result.