c++ - parsing 3 floats for glm::vec3 using boost::spirit::qi (error_invalid_expression) -

i can parse 1 float , print it. (test1, test2) somehow unable build rule parses 3 floats. final goal parse 3 floats , save them glm::vec3.

• my rule seems incorrect:

qi::lexeme[qi::float_ << ' ' << qi::float_ << ' ' << qi::float_]

• i not sure if using boost_fusion_adapt_struct correctly

here source show came far:

#include <iostream> #include <string> #include <glm\glm.hpp> #include <boost\spirit\include\qi.hpp> #include <boost\fusion\include\adapt_struct.hpp>  namespace qi = boost::spirit::qi;  void test1() {     std::string test = "1.2";     auto = test.begin();     if (qi::phrase_parse(it, test.end(), qi::float_, qi::space) && (it == test.end()))         std::cout << "test 1 ok" << std::endl;     else         std::cout << "test 1 not ok" << std::endl; }  void test2() {     std::string test = "1.2";     auto = test.begin();     float f;     if (qi::phrase_parse(it, test.end(), qi::float_, qi::space, f) && (it == test.end()))         std::cout << "test 2 ok " << f << std::endl;     else         std::cout << "test 2 not ok" << std::endl; }  void test3() {     std::string test = "1.2 2.2 3.3";     qi::rule<std::string::iterator, qi::space_type> vec3;     //error_invalid_expression     vec3 = qi::lexeme[qi::float_ << ' ' << qi::float_ << ' ' << qi::float_];     auto = test.begin();     if (qi::phrase_parse(it, test.end(), vec3, qi::space) && (it == test.end()))         std::cout << "test 3 ok " << std::endl;     else         std::cout << "test 3 not ok" << std::endl; }  boost_fusion_adapt_struct(     glm::vec3,     (float, x)     (float, y)     (float, z)     )  void test4() {     std::string test = "1.2 2.2 3.3";     qi::rule<std::string::iterator, qi::space_type> vec3;     //error_invalid_expression     vec3 = qi::lexeme[qi::float_ << ' ' << qi::float_ << ' ' << qi::float_];     glm::vec3 result;     auto = test.begin();     if (qi::phrase_parse(it, test.end(), vec3, qi::space, result) && (it == test.end()))     {         std::cout << "test 4 ok (" << result.x << ", " << result.y << ", " << result.z << ")"<< std::endl;     }     else         std::cout << "test 4 not ok" << std::endl; }  int main(int argc, char ** argv) {     test1();     test2();     test3();     test4(); } 

the test4 function contains try done.

edit:

as suggested 2 things need changed:

void test4() {     std::string test = "1.2 2.2 3.3";     qi::rule<std::string::iterator, glm::vec3(), qi::space_type> vec3;     //error_invalid_expression     vec3 = qi::lexeme[qi::float_ >> ' ' >> qi::float_ >> ' ' >> qi::float_];     glm::vec3 result;     auto = test.begin();     if (qi::phrase_parse(it, test.end(), vec3, qi::space, result) && (it == test.end()))     {         std::cout << "test 4 ok (" << result.x << ", " << result.y << ", " << result.z << ")"<< std::endl;     }     else         std::cout << "test 4 not ok" << std::endl; } 

the sequence parser operator >>, use instead of << in rules

vec3 = qi::lexeme[qi::float_ >> ' ' >> qi::float_ >> ' ' >> qi::float_]; 

you've specified whitespace skipper in rule, can further simplified removing lexeme directive , letting skipper skip spaces automatically (unless want ensure there single space character in between inputs).

vec3 = qi::float_ >> qi::float_ >> qi::float_; 

also, if want rule return value, need add signature rule type

qi::rule<std::string::iterator, glm::vec3(), qi::space_type> vec3; 

---

this unrelated compilation error you're seeing, use forward slashes in #include directives, works on platforms.

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