Add outline of numerical parsing example

Author: mborland

examples/numerical_parsing.cpp

@@ -0,0 +1,89 @@
+// Copyright 2025 Matt Borland
+// Distributed under the Boost Software License, Version 1.0.
+// https://www.boost.org/LICENSE_1_0.txt
+//
+// This file briefly demonstrates the difference in results when parsing monetary values between float and decimal32_t
+
+#include "where_file.hpp"
+#include <boost/decimal/decimal32_t.hpp>    // For type decimal32_t
+#include <boost/decimal/charconv.hpp>       // For support to <charconv>
+#include <boost/decimal/iostream.hpp>       // For decimal support to <iostream>
+#include <string>
+#include <vector>
+#include <fstream>
+#include <sstream>
+#include <limits>
+#include <numeric>
+#include <iostream>
+#include <iomanip>
+
+using boost::decimal::decimal32_t;
+
+template <typename T>
+T parse_opening_price(const std::string& line);
+
+template <>
+float parse_opening_price<float>(const std::string& line)
+{
+    const auto result {std::stof(line)};
+    return result;
+}
+
+template <>
+decimal32_t parse_opening_price<decimal32_t>(const std::string& line)
+{
+    decimal32_t result;
+    const auto r = from_chars(line, result);
+
+    if (!r)
+    {
+        // LCOV_EXCL_START
+        result = std::numeric_limits<decimal32_t>::quiet_NaN();
+        BOOST_DECIMAL_THROW_EXCEPTION(std::invalid_argument("Parsing has failed"));
+        // LCOV_EXCL_STOP
+    }
+
+    return result;
+}
+
+template <typename T>
+auto parse_csv_line(const std::string& line) -> T
+{
+    std::stringstream ss(line);
+    std::string token;
+    std::string date;
+
+    std::getline(ss, date, ',');
+    std::getline(ss, token, ',');
+
+    return parse_opening_price<T>(token);
+}
+
+int main()
+{
+    // Open and read the CSV file
+    std::ifstream file(boost::decimal::where_file("AAPL.csv"));
+    std::string line;
+
+    // Skip header line
+    std::getline(file, line);
+
+    std::vector<decimal32_t> decimal_opening_prices;
+    std::vector<float> float_opening_prices;
+
+    while (std::getline(file, line))
+    {
+        decimal_opening_prices.emplace_back(parse_csv_line<decimal32_t>(line));
+        float_opening_prices.emplace_back(parse_csv_line<float>(line));
+    }
+
+    const std::string ms_result {"52151.99"};
+    const auto decimal_sum {std::accumulate(decimal_opening_prices.begin(), decimal_opening_prices.end(), decimal32_t{0})};
+    const auto float_sum {std::accumulate(float_opening_prices.begin(), float_opening_prices.end(), float{0})};
+
+    std::cout << std::setprecision(std::numeric_limits<float>::digits10 + 1)
+              << "Number of data points: " << decimal_opening_prices.size() << '\n'
+              << "    Sum from MS Excel: " << ms_result << '\n'
+              << "Sum using decimal32_t: " << decimal_sum << '\n'
+              << "      Sum using float: " << float_sum << std::endl;
+}

test/Jamfile

@@ -206,6 +206,7 @@ run ../examples/format.cpp ;
 run ../examples/fmt_format.cpp ;
 run ../examples/print.cpp ;
 run ../examples/promotion.cpp ;
+run ../examples/numerical_parsing.cpp ;
 
 # Test compilation of separate headers
 compile compile_tests/bid_conversion.cpp ;