我正在尝试使用boost :: spirit库解析Newick语法（定义为here）。
我已经创建了自己的解析器，可以正确识别语法。这是代码：
#define BOOST_SPIRIT_DEBUG
#include <boost/spirit/include/qi.hpp>
#include <boost/variant/recursive_variant.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <vector>
namespace parser
{
struct ptree;
typedef boost::variant<boost::recursive_wrapper<ptree>> ptree_recursive;
struct ptree
{
std::vector<ptree_recursive> children;
std::string name;
double length;
};
/* Used to cast ptree_recursive into ptree. */
class ptree_visitor : public boost::static_visitor<ptree>
{
public:
ptree operator() (ptree tree) const
{
return tree;
}
};
}
BOOST_FUSION_ADAPT_STRUCT(
parser::ptree,
(std::vector<parser::ptree_recursive>, children)
(std::string, name)
(double, length)
)
namespace parser
{
namespace qi = boost::spirit::qi;
namespace ascii = boost::spirit::ascii;
template<typename Iterator>
struct newick_grammar : qi::grammar<Iterator, ptree(), ascii::space_type>
{
public:
newick_grammar() : newick_grammar::base_type(tree)
{
using qi::lexeme;
using qi::double_;
using ascii::char_;
/* This is the only grammar that works fine:
* http://evolution.genetics.washington.edu/phylip/newick_doc.html */
label = lexeme[+(char_ - ':' - ')' - ',')];
branch_length = ':' >> double_;
subtree =
-descendant_list
>> -label
>> -branch_length;
descendant_list =
'('
>> subtree
>> *(',' >> subtree )
>> ')';
tree = subtree >> ';';
BOOST_SPIRIT_DEBUG_NODE(label);
BOOST_SPIRIT_DEBUG_NODE(branch_length);
BOOST_SPIRIT_DEBUG_NODE(subtree);
BOOST_SPIRIT_DEBUG_NODE(descendant_list);
BOOST_SPIRIT_DEBUG_NODE(tree);
}
private:
/* grammar rules */
qi::rule<Iterator, ptree(), ascii::space_type> tree, subtree;
qi::rule<Iterator, ptree_recursive(), ascii::space_type> descendant_list;
qi::rule<Iterator, double(), ascii::space_type> branch_length;
qi::rule<Iterator, std::string(), ascii::space_type> label;
};
}
提供给解析器的ptree实例存储了newick树。 用于此代码的测试字符串如下：
(((One:0.1,Two:0.2)Sub1:0.3,(Three:0.4,Four:0.5)Sub2:0.6)Sub3:0.7,Five:0.8)Root:0.9;
解析器正确识别语法，但它会生成部分树。特别是，被恢复的ptree实例包含“Root”节点及其第一个“Sub3”子节点。 我尝试使用push_at和at_c方法（解释here）aswel。我有同样的结果。
为什么语法似乎没有创建和添加所有节点，甚至能够识别语法并在树上旅行？
感谢您的建议。
解
template<typename Iterator>
struct newick_grammar : qi::grammar<Iterator, base::ptree()>
{
public:
newick_grammar() : newick_grammar::base_type(tree)
{
/* This is the only grammar that works fine:
* http://evolution.genetics.washington.edu/phylip/newick_doc.html */
label %= qi::lexeme[+(qi::char_ - ':' - ')' - ',')];
branch_length %= ':' >> qi::double_;
subtree =
-descendant_list
>> -label
>> -branch_length;
descendant_list =
'('
>> subtree
>> *(',' >> subtree )
>> ')';
tree %= subtree >> ';';
BOOST_SPIRIT_DEBUG_NODE(label);
BOOST_SPIRIT_DEBUG_NODE(branch_length);
BOOST_SPIRIT_DEBUG_NODE(subtree);
BOOST_SPIRIT_DEBUG_NODE(descendant_list);
BOOST_SPIRIT_DEBUG_NODE(tree);
}
private:
/* grammar rules */
qi::rule<Iterator, base::ptree()> tree, subtree;
qi::rule<Iterator, base::children_ptree()> descendant_list;
qi::rule<Iterator, double()> branch_length;
qi::rule<Iterator, std::string()> label;
};
答案 0 :(得分：3)
我认为您的计划中有很多货物编码。例如，变体是完全无用的。所以我稍微重写了一下，添加评论以帮助您理解（我希望，如果不清楚，请不要犹豫，在评论中提问）。我把空间规范放在一边，因为我觉得它在你的情况下毫无用处。
#include <boost/spirit/include/qi.hpp>
#include <boost/fusion/include/adapt_struct.hpp>
#include <boost/spirit/include/phoenix_core.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/spirit/include/phoenix_fusion.hpp>
#include <boost/spirit/include/phoenix_stl.hpp>
#include <vector>
#include <string>
#include <iostream>
namespace parser
{
// Forward declaration for the vector
struct ptree;
// typedef to ease the writing
typedef std::vector<ptree> children_vector;
// The tree structure itseflf
struct ptree
{
children_vector children;
std::string name;
double length;
};
// Streaming operator for printing the result
std::ostream& operator<<(std::ostream& stream, const ptree& tree)
{
bool first = true;
stream << "(" << tree.name << ": " << tree.length << " { ";
for (auto child: tree.children)
{
stream << (first ? "" : "," ) << child;
first = false;
}
stream << " }";
return stream;
}
}
// adapt the structure to fusion phoenix
BOOST_FUSION_ADAPT_STRUCT(
parser::ptree,
(parser::children_vector, children)
(std::string, name)
(double, length)
)
namespace parser
{
// namespace aliasing to shorten the names
namespace qi = boost::spirit::qi;
namespace phoenix = boost::phoenix;
// This grammar parse string to a ptree
struct newick_grammar : qi::grammar<std::string::const_iterator, ptree()>
{
public:
newick_grammar()
: newick_grammar::base_type(tree) // We try to parse the tree rule
{
using phoenix::at_c; // Access nth field of structure
using phoenix::push_back; // Push into vector
// For label use %= to assign the result of the parse to the string
label %= qi::lexeme[+(qi::char_ - ':' - ')' - ',')];
// For branch length use %= to assign the result of the parse to the
// double
branch_length %= ':' >> qi::double_;
// When parsing the subtree just assign the elements that have been
// built in the subrules
subtree =
// Assign vector of children to the first element of the struct
-descendant_list [at_c<0>(qi::_val) = qi::_1 ]
// Assign the label to the second element
>> -label [ at_c<1>(qi::_val) = qi::_1 ]
// Assign the branch length to the third element
>> -branch_length [ at_c<2>(qi::_val) = qi::_1 ];
// Descendant list is a vector of ptree, we just push back the
// created ptrees into the vector
descendant_list =
'(' >> subtree [ push_back(qi::_val, qi::_1) ]
>> *(',' >> subtree [ push_back(qi::_val, qi::_1) ])
>> ')';
// The tree receive the whole subtree using %=
tree %= subtree >> ';' ;
}
private:
// Here are the various grammar rules typed by the element they do
// generate
qi::rule<std::string::const_iterator, ptree()> tree, subtree;
qi::rule<std::string::const_iterator, children_vector()> descendant_list;
qi::rule<std::string::const_iterator, double()> branch_length;
qi::rule<std::string::const_iterator, std::string()> label;
};
}
int main(int argc, char const *argv[])
{
namespace qi = boost::spirit::qi;
std::string str;
while (getline(std::cin, str))
{
// Instantiate grammar and tree
parser::newick_grammar grammar;
parser::ptree tree;
// Parse
bool result = qi::phrase_parse(str.cbegin(), str.cend(), grammar, qi::space, tree);
// Print the result
std::cout << "Parsing result: " << std::boolalpha << result << std::endl;
std::cout << tree << std::endl;
}
return 0;
}
以下是样本的输出：
$ ./a.exe
(((One:0.1,Two:0.2)Sub1:0.3,(Three:0.4,Four:0.5)Sub2:0.6)Sub3:0.7,Five:0.8)Root:0.9;
Parsing result: true
(Root: 0.9 { (Sub3: 0.7 { (Sub1: 0.3 { (One: 0.1 { },(Two: 0.2 { } },(Sub2: 0.6 { (Three: 0.4 { },(Four: 0.5 { } } },(Five: 0.8 { } }