Assignment, Concatenation, and Appending

The string class makes some operations simpler than is the case for arrays. For example, you can’t simply assign one array to another. But you can assign one string object to another:

char charr1[20];            // create an empty array
char charr2[20] = "jaguar"; // create an initialized array
string str1;                // create an empty string object
string str2 = "panther";    // create an initialized string
charr1 = charr2;            // INVALID, no array assignment
str1 = str2;                // VALID, object assignment ok

The string class simplifies combining strings. You can use the + operator to add two string objects together and the += operator to tack on a string to the end of an existing string object. Continuing with the preceding code, we have the following possibilities:

string str3;
str3 = str1 + str2;         // assign str3 the joined strings
str1 += str2;               // add str2 to the end of str1

Listing 4.8 illustrates these usages. Note that you can add and append C-style strings as well as string objects to a string object.

Listing 4.8. strtype2.cpp

// strtype2.cpp –- assigning, adding, and appending
#include <iostream>
#include <string>               // make string class available
int main()
{
    using namespace std;
    string s1 = "penguin";
    string s2, s3;

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

    return 0;
}

Recall that the escape sequence " represents a double quotation mark that is used as a literal character rather than as marking the limits of a string. Here is the output from the program in Listing 4.8:

You can assign one string object to another: s2 = s1
s1: penguin, s2: penguin
You can assign a C-style string to a string object.
s2 = "buzzard"
s2: buzzard
You can concatenate strings: s3 = s1 + s2
s3: penguinbuzzard
You can append strings.
s1 += s2 yields s1 = penguinbuzzard
s2 += " for a day" yields s2 = buzzard for a day