The string class

Now we can declare variables to be of type string, e.g.

string s1, s2, s3;

Internally, the string class stores the string as a null-terminated character array (as per our usual idea of strings), but also has a field indicating the size of the array. This allows the string class to ensure operations never run off the end of a string.

The string class also contains a number of routines which allow us to dynamically change the size of a string - again providing much more flexible handling.

In the sections below we outline a number of the key string methods. There are many more methods than this, but this provides a reasonable introduction.

Constructors

The default constructor, string(), creates an empty string. E.g.
string s1; // s is empty

We can initialize the string with a character array, e.g.
string s2("blah"); // s2 gets initializes as a 5-char array
// with a null terminator inserted

We can initialize a string from another string, e.g.
string s3(s2);

We can initialize a string as a repeated sequence of characters, e.g.
string s4(6, 'm'); // s4 contains "mmmmmm"

Overloaded operators

The assignment operator copies values (as usual), i.e. copies the appropriate string, and allocates the size appropriately
s1 = s2; // s1 gets a copy of s2 (array and size)
s1 = "blah";
s1 = 'x';

The traditional comparison operators have all been overloaded to compare strings, e.g.
if ((s1 == s2) && (s3 < s4)) {

The + operator is used for append, e.g.
s1 += s2; // append a copy of s2 to the end of s1
s3 = s1 + s2; // s3 gets a copy of s1 followed by a copy of s2
s1 += "blah"; // append "blah" and adjust the size of s1
s1 += 'x'; // append "x" and adjust the size of s1

Other methods

We can reset a string's values based on a substring of another,
s1.assign(s2, 1, 2); // copy the first 2 chars of s2 to s1,
// starting at position 1 of s1

We can insert a string inside another, e.g.
s1.insert(2, "foo"); // insert "foo" starting at position 2 of s1

We can change the size of the string (i.e. allocate more or less space for its array), e.g.
s1.resize(20); // s1 now has maximum size 20

We can determine the current length of the string (i.e. the length up to the null terminator, which is less than or equal to the total allocated space)
int len = s1.length();

We can get just the array part back using the c_str method, e.g.
char *sptr = s1.c_str();

We can search a string for the position at which a substring starts using the find method, e.g.
pos = s1.find(s2); // search s1 for substring s2
pos = s1.find("blah"); // search s1 for substring "blah"

The stack class

bool empty(); // is the stack empty?
void pop(); // remove (without returning) the top element
void push(element); // push the specified element on top
int size(); // get the current number of stacked elements
stack_type top(); // return a copy of whatever is on top

int main(int argc, char *argv[])
{
   string *s;
   stack<string> Stack1;
   for (int i = 0; i < argc; i++) {
       s = new string(argv[i]);
       Stack1.push(*s);
   }
}

The queue class

bool empty(); // is the queue empty?
queue_type back(); // returns a copy of the back element
queue_type front(); // returns a copy of the front element
void pop(); // dequeues the front element
void push(element); // enqueues at the back
int size(); // get the current number of queued elements

The list class

bool empty(); // is the list empty?
list_type back(); // return a copy of the back element
list_type front(); // return a copy of the front element
void merge(anotherlist); // merge in the contents of another list
void pop_front(); // remove the front element
void push_front(element); // add an element at the front
void push_rear(element); // add an element at the back
void remove(element); // remove ALL occurrences of the element
void reverse(); // reverse the order of the list
int size(); // get the current number of list elements
void sort(); // sort the list elements (ascending order)
void swap(anotherlist); // swap this list's contents with the other list's

The vector class

vector_type back(); // return a copy of the last vector element
vector_type front(); // return a copy of the first vector element
bool empty(); // is the vector empty?
void pop_back(); // remove the back element
void push_back(element); // add an element to the end of the vector
int size(); // get the current number of vector elements

vector<int> vec1(30,-1); // create a 30-element vector,
                         // initialize all elements to -1
vec1[7] = 45;

Iterators with the templated classes

These are generalizations of pointers, and allow you to cycle through the elements of the class with the use of ++ and --.

The classes include a begin() and end() method for the iterators and overload the ++ -- == != operators for the iterators.

An example of iterator use is shown below:

vector<int>  myvec;

std::vector<int>::iterator p;  // p will act like a pointer to a 
                               // single int within the vector

p = myvec.begin();  // p points at the first int in the vector

// set up a while loop to cycle through the vector contents,
//     one int at a time
while (p != myvec.end()) 
{
   int nextdata = (*p);       // make nextdata point at the current int
   cout << nextdata << endl;  // print it out
   p++;                       // make p point at the next int
}

std::classname<contenttype>::iterator variablename;

// declare some variables
list<int> L;
queue<float> Q;
vector<string> V;

// declare some appropriate iterator variables
std::list<int>::iterator my_list_iterator;
std::queue<float>::iterator my_queue_iterator;
std::vector<string>::iterator my_vector_iterator;

You can also use const_iterator, which (on dereferencing) gives you a read-only copy of the data element.