Sams Teach Yourself C++ in 21 Days

Working with Streams 615

17

One if by land

One if by

One if by land i?!

OUTPUT

The final line of output might look different on your computer because it

accesses memory that is not part of an initialized variable.

NOTE

This listing prints from a phrase. Each time it prints a different amount of the

phrase. On line 7, one phrase is created. On line 9, the integer fullLengthis set

to the length of the phrase using a global strlen()method that was included with the

string directive on line 2. Also set are two other length values that will be used; tooShort

is set to the length of the phrase (fullLength)minus four, and tooLongis set to the

length of the phrase plus six.

On line 13, the complete phrase is printed using write(). The length is set to the actual

length of the phrase, and the correct phrase is printed.

On line 14, the phrase is printed again, but it is four characters shorter than the full

phrase, and that is reflected in the output.

On line 15, the phrase is printed again, but this time write()is instructed to write an

extra six characters. After the phrase is written, the next six bytes of contiguous memory

are written. Anything could be in this memory, so your output might vary from what is

shown previously.

Manipulators, Flags, and Formatting Instructions ........................................

The output stream maintains a number of state flags, determining which base (decimal or

hexadecimal) to use, how wide to make the fields, and what character to use to fill in

fields. A state flag is a byte whose individual bits are each assigned a special meaning.

Manipulating bits in this way is discussed on Day 21, “What’s Next.” Each of ostream’s

flags can be set using member functions and manipulators.

Using cout.width()

The default width of your output will be just enough space to print the number, character,

or string in the output buffer. You can change this by using width().

Because width()is a member function, it must be invoked with a coutobject. It only

changes the width of the very next output field and then immediately reverts to the

default. Listing 17.12 illustrates its use.

ANALYSIS