Directive Testing if Parser Succeeded (matches[])

The matches[] directive executes the embedded parser and returns whether it succeeded matching.

// forwards to <boost/spirit/home/qi/directive/matches.hpp>
#include <boost/spirit/include/qi_matches.hpp>

Name
`boost::spirit::matches // alias: boost::spirit::qi::matches`

UnaryParser

Notation

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

Expression	Semantics
`matches[a]`	Execute the subject parser `a`, and return as its attribute whether it succeeded. The directive itself does always succeed.

Expression	Attribute
`matches[a]`	`bool`

The complexity is defined by the complexity of the subject parser, a

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

Some using declarations:

using boost::spirit::qi::matches;
using boost::spirit::qi::int_;

This parser tries to match an int and returns true a its attribute as it succeeded matching:

bool result = false;
test_parser_attr("345", matches[int_], result);
std::cout << std::boolalpha << result << std::endl; // should print: true

This parser tries to match an int as well and returns false as its attribute as it fails matching:

result = true;
test_parser_attr("abc", matches[int_], result);
std::cout << std::boolalpha << result << std::endl; // should print: false