Make a separate folder for lexical_casts examples, use those examples in documenation and assure that they successfully build and run (refs #9046)

[SVN r85828]

example/args_to_numbers.cpp

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+// Copyright 2013 Antony Polukhin
+
+// Distributed under the Boost Software License, Version 1.0.
+// (See the accompanying file LICENSE_1_0.txt
+// or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
+
+//[lexical_cast_args_example
+//`The following example treats command line arguments as a sequence of numeric data
+
+#include <boost/lexical_cast.hpp>
+#include <vector>
+
+int main(int /*argc*/, char * argv[])
+{
+    using boost::lexical_cast;
+    using boost::bad_lexical_cast;
+
+    std::vector<short> args;
+
+    while (*++argv)
+    {
+        try
+        {
+            args.push_back(lexical_cast<short>(*argv));
+        }
+        catch(const bad_lexical_cast &)
+        {
+            args.push_back(0);
+        }
+    }
+
+    // ...
+}
+
+//] [/lexical_cast_args_example]

example/generic_stringize.cpp

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+// Copyright 2013 Antony Polukhin
+
+// Distributed under the Boost Software License, Version 1.0.
+// (See the accompanying file LICENSE_1_0.txt
+// or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
+
+
+//[lexical_cast_stringize
+/*`
+    In this example we'll make a `stringize` method that accepts a sequence, converts
+    each element of the sequence into string and appends that string to the result.
+
+    Example is based on the example from the [@http://www.packtpub.com/boost-cplusplus-application-development-cookbook/book Boost C++ Application Development Cookbook]
+    by Antony Polukhin, ISBN 9781849514880.
+
+    Step 1: Making a functor that converts any type to a string and remembers result:
+*/
+
+#include <boost/lexical_cast.hpp>
+#include <boost/noncopyable.hpp>
+
+struct stringize_functor: boost::noncopyable {
+private:
+    std::string& result;
+
+public:
+    explicit stringize_functor(std::string& res)
+        : result(res)
+    {}
+
+    template <class T>
+    void operator()(const T& v) const {
+        result += boost::lexical_cast<std::string>(v);
+    }
+};
+
+//` Step 2: Applying `stringize_functor` to each element in sequence:
+#include <boost/fusion/include/for_each.hpp>
+template <class Sequence>
+std::string stringize(const Sequence& seq) {
+    std::string result;
+    boost::fusion::for_each(seq, stringize_functor(result));
+    return result;
+}
+
+//` Step 3: Using the `stringize` with different types:
+#include <iostream>
+#include <boost/fusion/adapted/boost_tuple.hpp>
+#include <boost/fusion/adapted/std_pair.hpp>
+
+int main() {
+    boost::tuple<char, int, char, int> decim('-', 10, 'e', 5);
+    std::pair<short, std::string> value_and_type(270, "Kelvin");
+
+    std::cout << stringize(decim) << '\n'   // outputs '-10e5'
+        << stringize(value_and_type);       // outputs '270Kelvin'
+}
+
+//] [/lexical_cast_stringize]

example/small_examples.cpp

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+// Copyright 2013 Antony Polukhin
+
+// Distributed under the Boost Software License, Version 1.0.
+// (See the accompanying file LICENSE_1_0.txt
+// or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
+
+#include <boost/lexical_cast.hpp>
+#include <string>
+#include <cstdio>
+
+//[lexical_cast_log_errno
+//`The following example uses numeric data in a string expression: 
+
+void log_message(const std::string &);
+
+void log_errno(int yoko)
+{
+    log_message("Error " + boost::lexical_cast<std::string>(yoko) + ": " + strerror(yoko));
+}
+
+//] [/lexical_cast_log_errno]
+
+
+//[lexical_cast_fixed_buffer
+//`The following example converts some number and puts it to file:
+
+void number_to_file(int number, FILE* file)
+{
+    typedef boost::array<char, 50> buf_t; // You can use std::array if your compiler supports it
+    buf_t buffer = boost::lexical_cast<buf_t>(number); // No dynamic memory allocation
+    fputs(buffer.begin(), file);
+}
+
+//] [/lexical_cast_fixed_buffer]
+
+//[lexical_cast_substring_conversion
+//`The following example takes part of the string and converts it to `int`:
+
+int convert_strings_part(const std::string& s, std::size_t pos, std::size_t n)
+{
+    return boost::lexical_cast<int>(s.data() + pos, n);
+}
+
+//] [/lexical_cast_substring_conversion]
+
+void log_message(const std::string &) {}
+
+int main()
+{
+    return 0;
+}
+

example/variant_to_long_double.cpp

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+// Copyright 2013 Antony Polukhin
+
+// Distributed under the Boost Software License, Version 1.0.
+// (See the accompanying file LICENSE_1_0.txt
+// or a copy at <http://www.boost.org/LICENSE_1_0.txt>.)
+
+
+//[lexical_cast_variant_to_long_double
+/*`
+    In this example we'll make a `to_long_double` method that converts value of the Boost.Variant to `long double`.
+*/
+
+#include <boost/lexical_cast.hpp>
+#include <boost/variant.hpp>
+#include <cassert>
+
+struct to_long_double_functor: boost::static_visitor<long double> {
+    template <class T>
+    long double operator()(const T& v) const {
+        // Lexical cast has many optimizations including optimizations for situations that usually 
+        // occur in generic programming, like std::string to std::string or arithmetic type to arithmetic type conversion. 
+        return boost::lexical_cast<long double>(v);
+    }
+};
+
+// Throws `boost::bad_lexical_cast` if value of the variant is not convertible to `long double`
+template <class Variant>
+long double to_long_double(const Variant& v) {
+    return boost::apply_visitor(to_long_double_functor(), v);
+}
+
+int main() {
+    boost::variant<char, int, std::string> v1('0'), v2("10.0001"), v3(1);
+
+    long double sum = to_long_double(v1) + to_long_double(v2) + to_long_double(v3);
+    assert(sum > 11 && sum < 11.1);
+}
+
+//] [/lexical_cast_variant_to_long_double]