Seven instructive examples how to use Boost Spirit

spirit4_struct.cpp

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+// Example how to use Boost Spirit to parse CSV data directly into a C++ struct
+//
+// This example is designed to read the file "stock_list.txt"
+
+#include <fstream>
+#include <iomanip>
+#include <iostream>
+#include <stdexcept>
+
+#include <boost/spirit/include/qi.hpp>
+#include <boost/spirit/include/phoenix.hpp>
+#include <boost/fusion/include/adapt_struct.hpp>
+
+namespace qi = boost::spirit::qi;
+namespace phx = boost::phoenix;
+
+/******************************************************************************/
+
+// Helper to run a parser, check for errors, and capture the results.
+template <typename Parser, typename ... Args>
+void ParseOrDie(const std::string& input, const Parser& p, Args&& ... args)
+{
+    std::string::const_iterator begin = input.begin(), end = input.end();
+    bool ok = qi::parse(begin, end, p, std::forward<Args>(args) ...);
+    if (!ok || begin != end) {
+        std::cout << "Unparseable: "
+                  << std::quoted(std::string(begin, end)) << std::endl;
+        throw std::runtime_error("Parse error");
+    }
+}
+
+/******************************************************************************/
+// Our simple stock struct: two strings and a double.
+
+struct Stock
+{
+    std::string symbol;
+    std::string name;
+    double price;
+
+    // constructors
+    Stock() { }
+    Stock(std::string symbol, std::string name, double price)
+        : symbol(symbol), name(name), price(price) { }
+
+    // and how to format it to cout
+    friend std::ostream& operator << (std::ostream& os, const Stock& s)
+    {
+        return os << "[Stock"
+                  << " symbol=" << std::quoted(s.symbol)
+                  << " name=" << std::quoted(s.name)
+                  << " price=" << s.price
+                  << "]";
+    }
+};
+
+/******************************************************************************/
+// First Grammar: use Boost Phoenix in semantic action to construct a Stock
+// object with parsed parameters
+
+class StockGrammar1 : public qi::grammar<
+    // new grammar, this time the result type is a "Stock" object!
+    std::string::const_iterator, Stock()>
+{
+public:
+    using Iterator = std::string::const_iterator;
+
+    StockGrammar1() : StockGrammar1::base_type(start)
+    {
+        // define name rule: returns all characters up to ';' as a string.
+        name %= *(~qi::char_(';'));
+
+        // parse a CSV line, and construct Stock object using the three symbols
+        // stored as qi::_1, .. qi::_3. Optionally allow a trailing ';'.
+        start = (name >> ';' >> name >> ';' >> qi::double_ >> -(qi::lit(';')))
+            [qi::_val = phx::construct<Stock>(qi::_1, qi::_2, qi::_3) ];
+    }
+
+    // a helper rule which parser a name
+    qi::rule<Iterator, std::string()> name;
+    // rule which actually parses a CSV line containing the information
+    qi::rule<Iterator, Stock()> start;
+};
+
+void test1_stream(std::istream& input)
+{
+    // function to read each line of input and parse it.
+    std::string line;
+    StockGrammar1 g;
+    while (std::getline(input, line)) {
+        Stock stock;
+        ParseOrDie(line, g, stock);
+        std::cout << stock << std::endl;
+    }
+}
+
+/******************************************************************************/
+// First Grammar: use Boost Fusion to instrument the Stock class and enable
+// automatic semantic actions
+
+BOOST_FUSION_ADAPT_STRUCT(
+    Stock,
+    (std::string, symbol)
+    (std::string, name)
+    (double, price)
+)
+
+class StockGrammar2
+    : public qi::grammar<std::string::const_iterator, Stock()>
+{
+public:
+    using Iterator = std::string::const_iterator;
+
+    StockGrammar2() : StockGrammar2::base_type(start)
+    {
+        name %= *(~qi::char_(';'));
+        // parse CSV line, and let Boost Fusion automatically map results into
+        // the Stock struct (this does not use the constructor).
+        start %= name >> ';' >> name >> ';' >> qi::double_ >> -(qi::lit(';'));
+    }
+
+    qi::rule<Iterator, std::string()> name;
+    qi::rule<Iterator, Stock()> start;
+};
+
+void test2_stream(std::istream& input)
+{
+    std::string line;
+    while (std::getline(input, line)) {
+        Stock stock;
+        ParseOrDie(line, StockGrammar2(), stock);
+        std::cout << stock << std::endl;
+    }
+}
+
+/******************************************************************************/
+
+int main(int argc, char* argv[])
+{
+    if (argc >= 2) {
+        std::ifstream in(argv[1]);
+        test1_stream(in);
+    }
+    else {
+        std::cout << "Reading stdin" << std::endl;
+        test2_stream(std::cin);
+    }
+    return 0;
+}
+
+/******************************************************************************/