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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

3.2. Converting Numbers to Strings

Problem

You have numeric types (int, float) and you need to put the results in a string, perhaps formatted a certain way.

Solution

There are a number of different ways to do this, all with benefits and drawbacks. The first technique I will present uses a stringstream class to store the string data, because it is part of the standard library and easy to use. This approach is presented in Example 3-3. See the discussion for alternative techniques.

Example 3-3. Formatting a number as a string

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

using namespace std;

int main() {

   stringstream ss;

   ss << "There are " << 9 << " apples in my cart.";
   cout << ss.str() << endl;  // stringstream::str() returns a string
                              // with the contents

   ss.str("");                   // Empty the string
   ss << showbase << hex << 16;  // Show the base in hexadecimal
   cout << "ss = " << ss.str() << endl;

   ss.str("");
   ss << 3.14;
   cout << "ss = " << ss.str() << endl;
}

The output of Example 3-3 looks like this:

There are 9 apples in my cart.
ss = 0x10
ss = 3.14

Discussion

A stringstream is a convenient way to put data into a string because it lets you use all of the formatting facilities provided by the standard input and output stream classes. In the simplest case in Example 3-3, I just use the left-shift operator (<<) to write a combination of text and numeric data to my string stream:

ss << "There are " << 9 << " apples in my cart.";

The << operator is overloaded for built-in types ...

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Publisher Resources

ISBN: 0596007612Supplemental ContentErrata Page