CODEWITHSUNDEEP
c++boostboost-spiritboost-spirit-qi
Tom
Tom

Reputation: 702

Segfault trying to use boost::spirit::qi parser in a class

I have been writing some parser code using boost::spirit and started getting a segfault.

I have simplified my code down as much as I can to make it easy to post, see below.

The segfault occurs during the pushback of the int when the parser calls back to addModule.

Valgrind claims that the vector v_modules is not initialised. Earlier in the code I can see that it IS initialised so I assume some memory trashing is occuring. I've tried rewriting it many time with this smaller testcase to no avail. Any help appreciated!

verilog.cpp:

#include "verilog.h"
#include <string>
#include <boost/spirit/include/qi.hpp>

Verilog::Verilog() {
  m_parser.verilog = this;
}
Verilog::~Verilog(){}

void Verilog::parse(string contents) {
  string::const_iterator iter = contents.begin();
  string::const_iterator end = contents.end();
  bool r = phrase_parse(iter,end,m_parser,boost::spirit::ascii::space);
}

void Verilog::addModule() {
  int new_mod = 1;
  v_modules.push_back(new_mod);
}

int main()
{
  Verilog* verilog = new Verilog();
  string contents = "hello";
  verilog->parse(contents);
}

verilog.h

#ifndef VERILOG_H
#define VERILOG_H

#include <iostream>
#include <string>
#include <boost/spirit/include/qi.hpp>
#include <boost/bind.hpp>

using namespace std;
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;

class Verilog
{

 public:
  Verilog();
  ~Verilog();
  void parse(string contents);
  void addModule() ;

  template <typename Iterator>
    struct verilog_parser : qi::grammar<Iterator, ascii::space_type>  
    {
    verilog_parser() : verilog_parser::base_type(module)
        {
          module = qi::eps[boost::bind(&Verilog::addModule, verilog)];
        }

      qi::rule<Iterator, ascii::space_type> module;

      Verilog* verilog;

    };

 private:
  std::vector<int>    v_modules;
  verilog_parser<string::const_iterator> m_parser;

};

#endif

Upvotes: 2

Views: 101

Answers (1)

sehe
sehe

Reputation: 393789

You're using a boost::bind which results in a temporary function object that refers to whatever the verilog member points to during construction of the grammar.

That's not gonna work.

You need a phoenix lazy actor, and you better make it refer to this->verilog by _reference if you wanted it to pick up the changed value once you set it from within the Verilog constructor.

To be honest, the code looks a bit clumsy. Why don't you use Spirit's attribute compatibility rules to automatically build vectors (or lists, sets, maps... etc) for you?

Here's a fix:

#include <boost/spirit/include/phoenix.hpp>
namespace phx = boost::phoenix;

// ... later

            module = qi::eps[phx::bind(&Verilog::addModule, phx::ref(verilog))];

Note this still leaves the leaked Verilog instance in main. Why do you use new in modern C++?

Integrating it:

Live On Coliru

#include <iostream>
#include <string>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/phoenix.hpp>
#include <boost/bind.hpp>

using namespace std;
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
namespace phx = boost::phoenix;

class Verilog {

  public:
    Verilog();
    ~Verilog();
    void parse(string contents);
    void addModule();

    template <typename Iterator> struct verilog_parser : qi::grammar<Iterator, ascii::space_type> {
        verilog_parser() : verilog_parser::base_type(module) {
            module = qi::eps[phx::bind(&Verilog::addModule, phx::ref(verilog))];
        }

        qi::rule<Iterator, ascii::space_type> module;

        Verilog *verilog;
    };

  private:
    std::vector<int> v_modules;
    verilog_parser<string::const_iterator> m_parser;
};

#include <string>
#include <boost/spirit/include/qi.hpp>

Verilog::Verilog() { m_parser.verilog = this; }
Verilog::~Verilog() {}

void Verilog::parse(string contents) {
    string::const_iterator iter = contents.begin();
    string::const_iterator end = contents.end();
    bool r = phrase_parse(iter, end, m_parser, boost::spirit::ascii::space);
}

void Verilog::addModule() {
    int new_mod = 1;
    v_modules.push_back(new_mod);
}

int main() {
    Verilog verilog;
    string contents = "hello";
    verilog.parse(contents);
}

Upvotes: 3

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