C++ Primer Plus

cout << "Dr. X.\n";   // easier than cout << "The Dr. X."  << endl;

Finally, you can use escape sequences based on the octal or hexadecimal codes for a character. For example, Ctrl+Z has an ASCII code of 26, which is 032 in octal and 0x1a in hexadecimal. You can represent this character with either of the following escape sequences: \032 or \x1a. You can make character constants out of these by enclosing them in single quotes, as in '\032', and you can use them as parts of a string, as in "hi\x1a there".

Tip

When you have a choice between using a numeric escape sequence or a symbolic escape sequence, as in \0x8 versus \b, use the symbolic code. The numeric representation is tied to a particular code, such as ASCII, but the symbolic representation works with all codes and is more readable.

Listing 3.7 demonstrates a few escape sequences. It uses the alert character to get your attention, the newline character to advance the cursor (one small step for a cursor, one giant step for cursorkind), and the backspace character to back the cursor one space to the left. (Houdini once painted a picture of the Hudson River using only escape sequences; he was, of course, a great escape artist.)

Listing 3.7. bondini.cpp

// bondini.cpp -- using escape sequences

#include

int main()

{

    using namespace std;

    cout << "\aOperation \"HyperHype\" is now activated!\n";

    cout << "Enter your agent code:________\b\b\b\b\b\b\b\b";

    long code;

    cin >> code;

    cout << "\aYou entered " << code << "...\n";

    cout << "\aCode verified! Proceed with Plan Z3!\n";

    return 0;

}

Note

Some systems might behave differently, displaying the \b as a small rectangle rather than backspacing, for example, or perhaps erasing while backspacing, perhaps ignoring \a.

When you start the program in Listing 3.7, it puts the following text onscreen:

Operation "HyperHype" is now activated!

Enter your agent code:________

After printing the underscore characters, the program uses the backspace character to back up the cursor to the first underscore. You can then enter your secret code and continue. Here’s a complete run:

Operation "HyperHype" is now activated!

Enter your agent code:42007007

You entered 42007007...

Code verified! Proceed with Plan Z3!

Universal Character Names

C++ implementations support a basic source character set—that is, the set of characters you can use to write source code. It consists of the letters (uppercase and lowercase) and digits found on a standard U.S. keyboard, the symbols, such as { and =, used in the C language, and a scattering of other characters, such as the space character. Then there is a basic execution character set, which includes characters that can be processed during the execution of a program (for example, characters read from a file or displayed on screen). This adds a few more characters, such as backspace and alert. The C++ Standard also allows an implementation to offer extended source character sets and extended execution character sets. Furthermore, those additional characters that qualify as letters can be used as part of the name of an identifier. Thus, a German implementation might allow you to use umlauted vowels, and a French implementation might allow accented vowels. C++ has a mechanism for representing such international characters that is independent of any particular keyboard: the use of universal character names.

Using universal character names is similar to using escape sequences. A universal character name begins either with \u or \U. The \u form is followed by 8 hexadecimal digits, and the \U form by 16 hexadecimal digits. These digits represent the ISO 10646 code point for the character. (ISO 10646 is an international standard under development that provides numeric codes for a wide range of characters. See “Unicode and ISO 10646,” later in this chapter.)

If your implementation supports extended characters, you can use universal character names in identifiers, as character constants, and in strings. For example, consider the following code:

int k\u00F6rper;

cout << "Let them eat g\u00E2teau.\n";

The ISO 10646 code point for ö is 00F6, and the code point for â is 00E2. Thus, this C++ code would set the variable name to körper and display the following output:

Let them eat gâteau.

If your system doesn’t support ISO 10646, it might display some other character for â or perhaps simply display the word gu00E2teau.

Actually, from the standpoint of readability, there’s not much point to using \u00F6 as part of a variable name, but an implementation that included the ö character as part of an extended source character set probably would also allow you to type that character from the keyboard.