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C++ Cookbook
book

C++ Cookbook

by D. Ryan Stephens, Christopher Diggins, Jonathan Turkanis, Jeff Cogswell
November 2005
Beginner to intermediate content levelBeginner to intermediate
594 pages
16h 23m
English
O'Reilly Media, Inc.
Content preview from C++ Cookbook

10.3. Writing Your Own Stream Manipulators

Problem

You need a stream manipulator that does something the standard ones can’t. Or, you want to have a single manipulator set several flags on the stream instead of calling a set of manipulators each time you want a particular format.

Solution

To write a manipulator that doesn’t take an argument (à la left), write a function that takes an ios_base parameter and sets stream flags on it. If you need a manipulator that takes an argument, see the discussion a little later. Example 10-4 shows how to write a manipulator that doesn’t take an argument.

Example 10-4. A simple stream manipulator

#include <iostream>
#include <iomanip>
#include <string>

using namespace std;

// make floating-point output look normal
inline ios_base& floatnormal(ios_base& io) {
   io.setf(0, ios_base::floatfield);
   return(io);
}
int main() {

   ios_base::fmtflags flags =  // Save old flags
      cout.flags();

   double pi = 22.0/7.0;

   cout << "pi = " << scientific   // Scientific mode
        << pi * 1000 << '\n';

   cout << "pi = " << floatnormal
        << pi << '\n';

   cout.flags(flags);
}

Discussion

There are two kinds of manipulators: those that accept arguments and those that don’t. Manipulators that take no arguments are easy to write. All you have to do is write a function that accepts a stream parameter, does something to it (sets a flag or changes a setting), and returns it. Writing a manipulator that takes one or more arguments is more complicated because you need to create additional classes and functions ...

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Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page