boost::lexical_cast

As an introduction to some of the most interesting boost libraries you can read "Beyond the C++ Standard Library: An Introduction to Boost", by Björn Karlsson, an Addison Wesley Professional book. That's what I'm actually doing, and these are a few notes that I'm jotting down in the meanwhile.

Converting data from strings to numeric types is a boring and error prone task, luckly we can use lexical_cast, as showed in this example:

#include <iostream>
#include <string>
#include "boost/lexical_cast.hpp"

using std::string;
using std::cout;
using std::endl;
using boost::lexical_cast;
using boost::bad_lexical_cast;

void lexical()
{
    // string to int
    string s("42");
    int i = lexical_cast<int>(s);
    cout << "fortytwo as string " << s << " and as int " << i << endl;

    // float to string
    float f = 3.14151;
    s = lexical_cast<std::string>(f);
    cout << "PI as float " << f << " and as string " << s << endl;

    // literal to double
    double d = lexical_cast<double>("2.52");
    cout << "A double from a string " << d << endl;

    // Failed conversion
    s = "Not an int";
    try
    {
        i = lexical_cast<int>(s);
    }
    catch(bad_lexical_cast& blc)
    {
        cout << "Exception " << blc.what() << endl;
    }
}

It is easy to think about a template function that would convert to a string its input:

#include <iostream>
#include <string>
#include "boost/lexical_cast.hpp"

using std::string;
using std::cout;
using std::endl;
using boost::lexical_cast;
using boost::bad_lexical_cast;

namespace
{
    template <typename T>
    string toString(const T& arg)
    {
        try {
            return lexical_cast<string>(arg);
        }
        catch(boost::bad_lexical_cast& e) {
            return "";
        }
    }
}

void lexical2()
{
    string s = toString(42);
    cout << "int to string " << s << endl;

    s = toString(3.14151);
    cout << "float to string " << s << endl;
}