I/O Operations

Manipulators Again

Use of the setf(), width(), and similar member functions is very convenient if the same specifications are used for a large number of inserted items.

If the formatting frequently changes, it is more convenient to use a manipulator.

A manipulator is an object that can be an operand to the << or >> operator, but which modifies the state of the stream, rather than actually inserting or extracting any data.

For instance, the manipulators hex and dec can be used to request hexadecimal or decimal printing of integral values.

Thus, the following sequence can be used to write out the value of i in decimal and the value of x[i] in hexadecimal:

cout << "i = " << dec << i << ",

x[i] = " << hex << x[i];

Other manipulators include the following:

ws skips white space on input.

flush flushes a stream's buffer.

endl inserts a newline character and then flushes the stream's buffer.

ends inserts an end-of-string character ( '\0' ).

It is possible to create user-defined manipulators in addition to the standard manipulators, but this is beyond the scope of this book.

See class IOMANIP for examples of user-defined manipulators, or refer to the C++ Programming Language, Second Edition for a detailed discussion.