用Boost.Spirit解析嵌套列表

Question

我想用Boost.Spirit来解析嵌套列表的数字。这是我到目前为止有：

//define a test string 
std::string string = "[[\t1 , 2 ], [3, 4, 65.4]]"; 
auto it = string.begin(); 

//parse the string 
std::vector<std::vector<double>> vector; 
auto listRule = "[" >> (qi::double_ % ",") >> "]"; 
auto list2Rule = "[" >> (listRule % ",") >> "]"; 
bool match = qi::phrase_parse(it, string.end(), list2Rule, ascii::space, vector); 

//check if we have a match 
std::cout << "matched: " << std::boolalpha << match << '\n'; 
if (it != string.end()) 
    std::cout << "unmatched part: " << std::string{it, string.end()} << '\n'; 

//print the result 
std::cout << "result\n"; 
for (const auto& v : vector) { 
    std::cout << "["; 
    for (double i : v) 
     std::cout << i << ","; 
    std::cout << "]\n"; 
} 

以上奇妙的作品和版画：

matched: true 
result 
[1,2,] 
[3,4,65.4,] 

我现在面临的问题是，它不接受空名单。例如，通过改变字符串像这样：

std::string string = "[[\t1 , 2 ], [3, 4, 65.4], []]"; 

然后我不匹配（即match == false和it == string.begin()）。显然，该矢量仍然被填充，但最后一个空列表丢失。任何人都可以提供解释，为什么这是这种情况，以及如何解决它？

Answer 1

您使用auto在齐域名原表达模板 - 这是不确定的行为的99.9％的时间：

• undefined behaviour somewhere in boost::spirit::qi::phrase_parse

现在，当你解决这个问题，也使表体可选：

Live On Coliru

个

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

int main() { 
    using It  = std::string::const_iterator; 
    using Skipper = qi::space_type; 

    for(std::string const input : { "[[\t1 , 2 ], [3, 4, 65.4]]", "[[\t1 , 2 ], [3, 4, 65.4], []]", "[]" }) 
    { 
     std::cout << " ---- '" << input << "' ----\n"; 
     auto it = input.begin(); 

     //parse the string 
     using doubles = std::vector<double>; 
     using vectors = std::vector<doubles>; 

     qi::rule<It, doubles(), Skipper> doubles_ = "[" >> -(qi::double_ % ",") >> "]"; 
     qi::rule<It, vectors(), Skipper> vectors_ = "[" >> -(doubles_ % ",") >> "]"; 

     vectors data; 
     bool match = qi::phrase_parse(it, input.end(), vectors_, qi::space, data); 

     //check if we have a match 
     std::cout << "matched: " << std::boolalpha << match << '\n'; 
     if (it != input.end()) 
      std::cout << "unmatched part: " << std::string{it, input.end()} << '\n'; 

     //print the result 
     std::cout << "result\n"; 
     for (const auto& v : data) { 
      std::cout << "["; 
      for (double i : v) 
       std::cout << i << ","; 
      std::cout << "]\n"; 
     } 
    } 
} 

打印

---- '[[ 1 , 2 ], [3, 4, 65.4]]' ---- 
matched: true 
result 
[1,2,] 
[3,4,65.4,] 
---- '[[ 1 , 2 ], [3, 4, 65.4], []]' ---- 
matched: true 
result 
[1,2,] 
[3,4,65.4,] 
[] 
---- '[]' ---- 
matched: true 
result