[英]Troubles with boost::spirit::lex & whitespace
I try learning to use boost::spirit. 我尝试学习使用boost :: spirit。 To do that, I wanted to create some simple lexer, combine them and then start parsing using spirit. 为此,我想创建一些简单的词法分析器,将它们组合起来,然后使用精神开始解析。 I tried modifying the example, but it doesn't run as expected (the result r isn't true). 我尝试修改示例,但它没有按预期运行(结果r不正确)。
Here's the lexer: 这是词法分析器:
#include <boost/spirit/include/lex_lexertl.hpp>
namespace lex = boost::spirit::lex;
template <typename Lexer>
struct lexer_identifier : lex::lexer<Lexer>
{
lexer_identifier()
: identifier("[a-zA-Z_][a-zA-Z0-9_]*")
, white_space("[ \\t\\n]+")
{
using boost::spirit::lex::_start;
using boost::spirit::lex::_end;
this->self = identifier;
this->self("WS") = white_space;
}
lex::token_def<> identifier;
lex::token_def<> white_space;
std::string identifier_name;
};
And this is the example I'm trying to run: 这是我正在尝试运行的示例:
#include "stdafx.h"
#include <boost/spirit/include/lex_lexertl.hpp>
#include "my_Lexer.h"
namespace lex = boost::spirit::lex;
int _tmain(int argc, _TCHAR* argv[])
{
typedef lex::lexertl::token<char const*,lex::omit, boost::mpl::false_> token_type;
typedef lex::lexertl::lexer<token_type> lexer_type;
typedef lexer_identifier<lexer_type>::iterator_type iterator_type;
lexer_identifier<lexer_type> my_lexer;
std::string test("adedvied das934adf dfklj_03245");
char const* first = test.c_str();
char const* last = &first[test.size()];
lexer_type::iterator_type iter = my_lexer.begin(first, last);
lexer_type::iterator_type end = my_lexer.end();
while (iter != end && token_is_valid(*iter))
{
++iter;
}
bool r = (iter == end);
return 0;
}
r is true as long as there is only one token inside the string. 只要字符串中只有一个标记,r就为真。 Why is this the case? 为什么会这样?
Regards Tobias 关心托比亚斯
You have created a second lexer state, but never invoked it. 您已创建第二个词法分析器状态,但从未调用它。
For most cases, the easiest way to have the desired effect would be to use single-state lexing with a pass_ignore
flag on the skippable tokens: 在大多数情况下,获得所需效果的最简单方法是在可跳过的令牌上使用带有pass_ignore
标志的单状态lexing:
this->self += identifier
| white_space [ lex::_pass = lex::pass_flags::pass_ignore ];
Note that this requires an actor_lexer
to allow for the semantic action: 请注意,这需要一个actor_lexer
来允许语义操作:
typedef lex::lexertl::actor_lexer<token_type> lexer_type;
Full sample: 完整样本:
#include <boost/spirit/include/lex_lexertl.hpp>
#include <boost/spirit/include/lex_lexertl.hpp>
namespace lex = boost::spirit::lex;
template <typename Lexer>
struct lexer_identifier : lex::lexer<Lexer>
{
lexer_identifier()
: identifier("[a-zA-Z_][a-zA-Z0-9_]*")
, white_space("[ \\t\\n]+")
{
using boost::spirit::lex::_start;
using boost::spirit::lex::_end;
this->self += identifier
| white_space [ lex::_pass = lex::pass_flags::pass_ignore ];
}
lex::token_def<> identifier;
lex::token_def<> white_space;
std::string identifier_name;
};
int main(int argc, const char *argv[])
{
typedef lex::lexertl::token<char const*,lex::omit, boost::mpl::false_> token_type;
typedef lex::lexertl::actor_lexer<token_type> lexer_type;
typedef lexer_identifier<lexer_type>::iterator_type iterator_type;
lexer_identifier<lexer_type> my_lexer;
std::string test("adedvied das934adf dfklj_03245");
char const* first = test.c_str();
char const* last = &first[test.size()];
lexer_type::iterator_type iter = my_lexer.begin(first, last);
lexer_type::iterator_type end = my_lexer.end();
while (iter != end && token_is_valid(*iter))
{
++iter;
}
bool r = (iter == end);
std::cout << std::boolalpha << r << "\n";
}
Prints 打印
true
It is also possible you came across a sample that uses the second parser state for the skipper ( lex::tokenize_and_phrase_parse
). 您也可能遇到了一个使用第二个解析器状态的示例( lex::tokenize_and_phrase_parse
)。 Let me take a minute or 10 to create a working sample for that. 让我花一分钟或10分钟为此创建一个工作样本。
Update Took me a bit more than 10 minutes (waaaah) :) Here's a comparative test, showing how the lexer states interact, and how to use Spirit Skipper parsing to invoke the second parser state: 更新花了我超过10分钟(waaaah):)这是一个比较测试,显示词法分析器状态如何相互作用,以及如何使用Spirit Skipper解析来调用第二个解析器状态:
#include <boost/spirit/include/qi.hpp>
#include <boost/spirit/include/lex_lexertl.hpp>
namespace lex = boost::spirit::lex;
namespace qi = boost::spirit::qi;
template <typename Lexer>
struct lexer_identifier : lex::lexer<Lexer>
{
lexer_identifier()
: identifier("[a-zA-Z_][a-zA-Z0-9_]*")
, white_space("[ \\t\\n]+")
{
this->self = identifier;
this->self("WS") = white_space;
}
lex::token_def<> identifier;
lex::token_def<lex::omit> white_space;
};
int main()
{
typedef lex::lexertl::token<char const*, lex::omit, boost::mpl::true_> token_type;
typedef lex::lexertl::lexer<token_type> lexer_type;
typedef lexer_identifier<lexer_type>::iterator_type iterator_type;
lexer_identifier<lexer_type> my_lexer;
std::string test("adedvied das934adf dfklj_03245");
{
char const* first = test.c_str();
char const* last = &first[test.size()];
// cannot lex in just default WS state:
bool ok = lex::tokenize(first, last, my_lexer, "WS");
std::cout << "Starting state WS:\t" << std::boolalpha << ok << "\n";
}
{
char const* first = test.c_str();
char const* last = &first[test.size()];
// cannot lex in just default state either:
bool ok = lex::tokenize(first, last, my_lexer, "INITIAL");
std::cout << "Starting state INITIAL:\t" << std::boolalpha << ok << "\n";
}
{
char const* first = test.c_str();
char const* last = &first[test.size()];
bool ok = lex::tokenize_and_phrase_parse(first, last, my_lexer, *my_lexer.self, qi::in_state("WS")[my_lexer.self]);
ok = ok && (first == last); // verify full input consumed
std::cout << std::boolalpha << ok << "\n";
}
}
The output is 输出是
Starting state WS: false
Starting state INITIAL: false
true
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