我有一个非常简单的路径构造,我试图用boost spirit.lex解析。
我们有以下语法:
token := [a-z]+
path := (token : path) | (token)
所以我们这里只讨论冒号分隔的小写ASCII字符串。
我有三个例子“xyz”,“abc:xyz”,“abc:xyz:”。
前两项应视为有效。第三个,有一个尾随结肠,不应被视为有效。不幸的是,解析器我已经认识到这三个都是有效的。语法不应该允许空令牌,但显然精神就是这样做的。为了让第三个被拒绝,我错过了什么?
此外,如果您阅读下面的代码,则在注释中还有另一个版本的解析器要求所有路径以分号结尾。当我激活这些行时,我可以得到适当的行为(即拒绝“abc:xyz:;”),但这不是我想要的。
有人有什么想法吗?
感谢。
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/lex_lexertl.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <iostream>
#include <string>
using namespace boost::spirit;
using boost::phoenix::val;
template<typename Lexer>
struct PathTokens : boost::spirit::lex::lexer<Lexer>
{
PathTokens()
{
identifier = "[a-z]+";
separator = ":";
this->self.add
(identifier)
(separator)
(';')
;
}
boost::spirit::lex::token_def<std::string> identifier, separator;
};
template <typename Iterator>
struct PathGrammar
: boost::spirit::qi::grammar<Iterator>
{
template <typename TokenDef>
PathGrammar(TokenDef const& tok)
: PathGrammar::base_type(path)
{
using boost::spirit::_val;
path
=
(token >> tok.separator >> path)[std::cerr << _1 << "\n"]
|
//(token >> ';')[std::cerr << _1 << "\n"]
(token)[std::cerr << _1 << "\n"]
;
token
= (tok.identifier) [_val=_1]
;
}
boost::spirit::qi::rule<Iterator> path;
boost::spirit::qi::rule<Iterator, std::string()> token;
};
int main()
{
typedef std::string::iterator BaseIteratorType;
typedef boost::spirit::lex::lexertl::token<BaseIteratorType, boost::mpl::vector<std::string> > TokenType;
typedef boost::spirit::lex::lexertl::lexer<TokenType> LexerType;
typedef PathTokens<LexerType>::iterator_type TokensIterator;
typedef std::vector<std::string> Tests;
Tests paths;
paths.push_back("abc");
paths.push_back("abc:xyz");
paths.push_back("abc:xyz:");
/*
paths.clear();
paths.push_back("abc;");
paths.push_back("abc:xyz;");
paths.push_back("abc:xyz:;");
*/
for ( Tests::iterator iter = paths.begin(); iter != paths.end(); ++iter )
{
std::string str = *iter;
std::cerr << "*****" << str << "*****\n";
PathTokens<LexerType> tokens;
PathGrammar<TokensIterator> grammar(tokens);
BaseIteratorType first = str.begin();
BaseIteratorType last = str.end();
bool r = boost::spirit::lex::tokenize_and_parse(first, last, tokens, grammar);
std::cerr << r << " " << (first==last) << "\n";
}
}
答案 0 :(得分:5)
除了llonesmiz已经说过的内容之外,这里有一个使用qi::eoi
的技巧,我有时会使用它:
path = (
(token >> tok.separator >> path) [std::cerr << _1 << "\n"]
| token [std::cerr << _1 << "\n"]
) >> eoi;
这使得语法需要 eoi
(输入结束)在成功匹配结束时。这导致了期望的结果:
http://liveworkspace.org/code/23a7adb11889bbb2825097d7c553f71d
*****abc*****
abc
1 1
*****abc:xyz*****
xyz
abc
1 1
*****abc:xyz:*****
xyz
abc
0 1
答案 1 :(得分:3)
问题在于您致电first
后last
和tokenize_and_parse
的含义。 first==last
检查您的字符串是否已完全标记化,您无法推断语法的任何内容。如果您像这样隔离解析,则获得预期结果:
PathTokens<LexerType> tokens;
PathGrammar<TokensIterator> grammar(tokens);
BaseIteratorType first = str.begin();
BaseIteratorType last = str.end();
LexerType::iterator_type lexfirst = tokens.begin(first,last);
LexerType::iterator_type lexlast = tokens.end();
bool r = parse(lexfirst, lexlast, grammar);
std::cerr << r << " " << (lexfirst==lexlast) << "\n";
答案 2 :(得分:2)
这就是我最终的结果。它使用了@sehe和@llonesmiz的建议。请注意转换为std :: wstring以及语法定义中的操作的使用,这些操作在原始帖子中不存在。
#include <boost/config/warning_disable.hpp>
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/lex_lexertl.hpp>
#include <boost/spirit/include/phoenix_operator.hpp>
#include <boost/bind.hpp>
#include <iostream>
#include <string>
//
// This example uses boost spirit to parse a simple
// colon-delimited grammar.
//
// The grammar we want to recognize is:
// identifier := [a-z]+
// separator = :
// path= (identifier separator path) | identifier
//
// From the boost spirit perspective this example shows
// a few things I found hard to come by when building my
// first parser.
// 1. How to flag an incomplete token at the end of input
// as an error. (use of boost::spirit::eoi)
// 2. How to bind an action on an instance of an object
// that is taken as input to the parser.
// 3. Use of std::wstring.
// 4. Use of the lexer iterator.
//
// This using directive will cause issues with boost::bind
// when referencing placeholders such as _1.
// using namespace boost::spirit;
//! A class that tokenizes our input.
template<typename Lexer>
struct Tokens : boost::spirit::lex::lexer<Lexer>
{
Tokens()
{
identifier = L"[a-z]+";
separator = L":";
this->self.add
(identifier)
(separator)
;
}
boost::spirit::lex::token_def<std::wstring, wchar_t> identifier, separator;
};
//! This class provides a callback that echoes strings to stderr.
struct Echo
{
void echo(boost::fusion::vector<std::wstring> const& t) const
{
using namespace boost::fusion;
std::wcerr << at_c<0>(t) << "\n";
}
};
//! The definition of our grammar, as described above.
template <typename Iterator>
struct Grammar : boost::spirit::qi::grammar<Iterator>
{
template <typename TokenDef>
Grammar(TokenDef const& tok, Echo const& e)
: Grammar::base_type(path)
{
using boost::spirit::_val;
path
=
((token >> tok.separator >> path)[boost::bind(&Echo::echo, e,::_1)]
|
(token)[boost::bind(&Echo::echo, &e, ::_1)]
) >> boost::spirit::eoi; // Look for end of input.
token
= (tok.identifier) [_val=boost::spirit::qi::_1]
;
}
boost::spirit::qi::rule<Iterator> path;
boost::spirit::qi::rule<Iterator, std::wstring()> token;
};
int main()
{
// A set of typedefs to make things a little clearer. This stuff is
// well described in the boost spirit documentation/examples.
typedef std::wstring::iterator BaseIteratorType;
typedef boost::spirit::lex::lexertl::token<BaseIteratorType, boost::mpl::vector<std::wstring> > TokenType;
typedef boost::spirit::lex::lexertl::lexer<TokenType> LexerType;
typedef Tokens<LexerType>::iterator_type TokensIterator;
typedef LexerType::iterator_type LexerIterator;
// Define some paths to parse.
typedef std::vector<std::wstring> Tests;
Tests paths;
paths.push_back(L"abc");
paths.push_back(L"abc:xyz");
paths.push_back(L"abc:xyz:");
paths.push_back(L":");
// Parse 'em.
for ( Tests::iterator iter = paths.begin(); iter != paths.end(); ++iter )
{
std::wstring str = *iter;
std::wcerr << L"*****" << str << L"*****\n";
Echo e;
Tokens<LexerType> tokens;
Grammar<TokensIterator> grammar(tokens, e);
BaseIteratorType first = str.begin();
BaseIteratorType last = str.end();
// Have the lexer consume our string.
LexerIterator lexFirst = tokens.begin(first, last);
LexerIterator lexLast = tokens.end();
// Have the parser consume the output of the lexer.
bool r = boost::spirit::qi::parse(lexFirst, lexLast, grammar);
// Print the status and whether or note all output of the lexer
// was processed.
std::wcerr << r << L" " << (lexFirst==lexLast) << L"\n";
}
}