Methods for Appending and Adding

You can append one string to another by using the overloaded += operator or by using an append() method. All throw a length_error exception if the result would be longer than the maximum string size. The += operators let you append a string object, a string array, or an individual character to another string:

basic_string& operator+=(const basic_string& str);
basic_string& operator+=(const charT* s);
basic_string& operator+=(charT c);

The append() methods also let you append a string object, a string array, or an individual character to another string. In addition, they let you append part of a string object by specifying an initial position and a number of characters to append or else by specifying a range. You can append part of a string by specifying how many characters of the string to use. The version for appending a character lets you specify how many instances of that character to copy. Here are the prototypes for the various append() methods:

basic_string& append(const basic_string& str);
basic_string& append(const basic_string& str, size_type pos,
                     size_type n);
template<class InputIterator>
  basic_string& append(InputIterator first, InputIterator last);
basic_string& append(const charT* s);
basic_string& append(const charT* s, size_type n);
basic_string& append(size_type n, charT c);  // append n copies of c
void push_back(charT c);                     // appends 1 copy of c

Here are a couple examples:

string test("The");
test.append("ory");  // test is "Theory"
test.append(3,'!'),  // test is "Theory!!!"

The operator+() function is overloaded to enable string concatenation. The overloaded functions don’t modify a string; instead, they create a new string that consists of one string appended to a second. The addition functions are not member functions, and they allow you to add a string object to a string object, a string array to a string object, a string object to a string array, a character to a string object, and a string object to a character. Here are some examples:

string st1("red");
string st2("rain");
string st3 = st1 + "uce";  // st3 is "reduce"
string st4 = 't' + st2;    // st4 is "train"
string st5 = st1 + st2;    // st5 is "redrain"