Boost C++ Libraries of the most highly regarded and expertly designed C++ library projects in the world. Herb Sutter and Andrei Alexandrescu, C++ Coding Standards

This is the documentation for an old version of Boost. Click here to view this page for the latest version.
Sequence Parser (a >> b)

The sequence operator, a >> b, parses two or more operands (a, b, ... etc.), in sequence:

a >> b >> ...
// forwards to <boost/spirit/home/qi/operator/sequence.hpp>
#include <boost/spirit/include/qi_sequence.hpp>

Also, see Include Structure.

Model of



a, b

A Parser

Expression Semantics

Semantics of an expression is defined only where it differs from, or is not defined in NaryParser.



a >> b

Match a followed by b.


See Compound Attribute Notation.



a >> b

a: A, b: B --> (a >> b): tuple<A, B>
a: A, b: Unused --> (a >> b): A
a: Unused, b: B --> (a >> b): B
a: Unused, b: Unused --> (a >> b): Unused

a: A, b: A --> (a >> b): vector<A>
a: vector<A>, b: A --> (a >> b): vector<A>
a: A, b: vector<A> --> (a >> b): vector<A>
a: vector<A>, b: vector<A> --> (a >> b): vector<A>


The overall complexity of the sequence parser is defined by the sum of the complexities of its elements. The complexity of the sequence itself is O(N), where N is the number of elements in the sequence.


Some using declarations:

using boost::spirit::ascii::char_;
using boost::spirit::qi::_1;
using boost::spirit::qi::_2;
namespace bf = boost::fusion;

[Note] Note

The test harness for the example(s) below is presented in the Basics Examples section.

Simple usage:

test_parser("xy", char_ >> char_);

Extracting the attribute tuple (using Boost.Fusion):

bf::vector<char, char> attr;
test_parser_attr("xy", char_ >> char_, attr);
std::cout << bf::at_c<0>(attr) << ',' << bf::at_c<1>(attr) << std::endl;

Extracting the attribute vector (using STL):

std::vector<char> vec;
test_parser_attr("xy", char_ >> char_, vec);
std::cout << vec[0] << ',' << vec[1] << std::endl;

Extracting the attributes using Semantic Actions (using Boost.Phoenix):

test_parser("xy", (char_ >> char_)[std::cout << _1 << ',' << _2 << std::endl]);