Update
This question touches on two issues (as shown by the accepted answer), both of which are present in the version of Boost Spirit X3 that ships with Boost 1.64, but both of which are now fixed (or at least detected at compile time) in develop branch at the time of writing (2017-04-30).
I have updated the mcve project to reflect the changes that I made to use the develop branch instead of the latest boost release, in the hopes that it might help out others who face a similar issues.
The original question
I am trying to learn how to break up Spirit X3 parsers into separate reusable grammars, as encouraged by the example code (rexpr_full and calc in particular) and the presentations from CppCon 2015 and BoostCon.
I have a symbol table (essentially mapping different types to a enum class of the types I am supporting), which I would like to reuse in several parsers. The only example of symbol tables I could find is the roman numerals example, which is in a single source file.
When I try to move the symbol table into its own cpp/h file in the style of the more structured examples my parser will segfault if I try to parse any string which is not in the symbol table. If the symbol table is defined in the same compilation unit as the parsers that use it throws an expectation exception instead (which is what I would expect it to do).
With BOOST_SPIRIT_X3_DEBUG defined I get the following output:
<FruitType>
<try>GrannySmith: Mammals</try>
<Identifier>
<try>GrannySmith: Mammals</try>
<success>: Mammals</success>
<attributes>[[
Process finished with exit code 11
I have made a small project which shows what I am trying to achieve and is available here: https://github.com/sigbjornlo/spirit_fruit_mcve
My questions:
- Why does moving the symbol parser to a separate compilation unit cause a segmentation fault in this case?
- What is the recommended way of making a symbol table reusable in multiple parsers? (In the MCVE I obviously only use the
fruitparser in one other parser, but in my full project I want to use it in several other parsers.)
Below is the code for the MCVE project:
main.cpp
#include <iostream>
#define BOOST_SPIRIT_X3_DEBUG
#include <boost/spirit/home/x3.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include "common.h"
#include "fruit.h"
namespace ast {
struct FruitType {
std::string identifier;
FRUIT fruit;
};
}
BOOST_FUSION_ADAPT_STRUCT(ast::FruitType, identifier, fruit);
namespace parser {
// Identifier
using identifier_type = x3::rule<class identifier, std::string>;
const auto identifier = identifier_type {"Identifier"};
const auto identifier_def = x3::raw[x3::lexeme[(x3::alpha | '_') >> *(x3::alnum | '_')]];
BOOST_SPIRIT_DEFINE(identifier);
// FruitType
struct fruit_type_class;
const auto fruit_type = x3::rule<fruit_type_class, ast::FruitType> {"FruitType"};
// Using the sequence operator creates a grammar which fails gracefully given invalid input.
// const auto fruit_type_def = identifier >> ':' >> make_fruit_grammar();
// Using the expectation operator causes EXC_BAD_ACCESS exception with invalid input.
// Instead, I would have expected an expectation failure exception.
// Indeed, an expectation failure exception is thrown when the fruit grammar is defined here in this compilation unit instead of in fruit.cpp.
const auto fruit_type_def = identifier > ':' > make_fruit_grammar();
BOOST_SPIRIT_DEFINE(fruit_type);
}
int main() {
std::string input = "GrannySmith: Mammals";
parser::iterator_type it = input.begin(), end = input.end();
const auto& grammar = parser::fruit_type;
auto result = ast::FruitType {};
bool successful_parse = boost::spirit::x3::phrase_parse(it, end, grammar, boost::spirit::x3::ascii::space, result);
if (successful_parse && it == end) {
std::cout << "Parsing succeeded!\n";
std::cout << result.identifier << " is a kind of " << to_string(result.fruit) << "!\n";
} else {
std::cout << "Parsing failed!\n";
}
return 0;
}
std::string to_string(FRUIT fruit) {
switch (fruit) {
case FRUIT::APPLES:
return "apple";
case FRUIT::ORANGES:
return "orange";
}
}
common.h
#ifndef SPIRIT_FRUIT_COMMON_H
#define SPIRIT_FRUIT_COMMON_H
namespace x3 = boost::spirit::x3;
enum class FRUIT {
APPLES,
ORANGES
};
std::string to_string(FRUIT fruit);
namespace parser {
using iterator_type = std::string::const_iterator;
using context_type = x3::phrase_parse_context<x3::ascii::space_type>::type;
}
#endif //SPIRIT_FRUIT_COMMON_H
fruit.h
#ifndef SPIRIT_FRUIT_FRUIT_H
#define SPIRIT_FRUIT_FRUIT_H
#include <boost/spirit/home/x3.hpp>
#include "common.h"
namespace parser {
struct fruit_class;
using fruit_grammar = x3::rule<fruit_class, FRUIT>;
BOOST_SPIRIT_DECLARE(fruit_grammar)
fruit_grammar make_fruit_grammar();
}
#endif //SPIRIT_FRUIT_FRUIT_H
fruit.cpp
#include "fruit.h"
namespace parser {
struct fruit_symbol_table : x3::symbols<FRUIT> {
fruit_symbol_table() {
add
("Apples", FRUIT::APPLES)
("Oranges", FRUIT::ORANGES);
}
};
struct fruit_class;
const auto fruit = x3::rule<fruit_class, FRUIT> {"Fruit"};
const auto fruit_def = fruit_symbol_table {};
BOOST_SPIRIT_DEFINE(fruit);
BOOST_SPIRIT_INSTANTIATE(fruit_grammar, iterator_type, context_type);
fruit_grammar make_fruit_grammar() {
return fruit;
}
}
