Introducing strings
While a character array can be fairly
useful, it is quite limited. It’s simply a group of characters in memory,
but if you want to do anything with it you must manage all the little details.
For example, the size of a quoted character array is fixed at compile time. If
you have a character array and you want to add some more characters to it,
you’ll need to understand quite a lot (including dynamic memory
management, character array copying, and concatenation) before you can get your
wish. This is exactly the kind of thing we’d like to have an object do for
us.
The Standard C++
string class is designed to take care of (and
hide) all the low-level manipulations of character arrays that were previously
required of the C programmer. These manipulations have been a constant source of
time-wasting and errors since the inception of the C language. So, although an
entire chapter is devoted to the string class in Volume 2 of this book,
the string is so important and it makes life so much easier that it will
be introduced here and used in much of the early part of the
book.
To use strings you include the C++
header file <string>. The string class is in the namespace
std so a using directive is necessary. Because of operator
overloading, the syntax for using strings is quite
intuitive:
//: C02:HelloStrings.cpp
// The basics of the Standard C++ string class
#include <string>
#include <iostream>
using namespace std;
int main() {
string s1, s2; // Empty strings
string s3 = "Hello, World."; // Initialized
string s4("I am"); // Also initialized
s2 = "Today"; // Assigning to a string
s1 = s3 + " " + s4; // Combining strings
s1 += " 8 "; // Appending to a string
cout << s1 + s2 + "!" << endl;
} ///:~
The first two strings, s1
and s2, start out empty, while s3 and s4 show two
equivalent ways to initialize string objects from character arrays (you
can just as easily initialize string objects from other string
objects).
You can assign to any string
object using ‘=’. This replaces the previous contents of the
string with whatever is on the right-hand side, and you don’t have to
worry about what happens to the previous contents – that’s handled
automatically for you. To combine strings you simply use the
‘+’ operator, which also allows you to combine character
arrays with strings. If you want to append either a string or a
character array to another string, you can use the operator
‘+=’. Finally, note that iostreams
already know what to do with strings, so you can just send a
string (or an expression that produces a string, which happens
with s1 + s2 + "!") directly to cout in order to print
it.
