我的数据定义为
std::string data("START34*23*43**");
我的语法。
"START" >> boost::spirit::hex % '*'
问题:如何解析有两颗星的消息结尾?
不太清楚你要问什么。假设你只是想 "忽略"(或接受)尾部的星号,这里是你的罪魁祸首。
if (first != last) // fail if we did not get a full match
return false;
只要删除这些行就可以了
"活在科利鲁 (注大大简化)。
#include <boost/spirit/include/qi.hpp>
#include <iomanip>
namespace qi = boost::spirit::qi;
template <typename Iterator>
bool parse_numbers(Iterator& first, Iterator last, std::vector<unsigned>& v) {
return qi::phrase_parse(first, last, ("START" >> qi::hex % '*'), qi::space, v);
}
int main() {
for (std::string const data : {
"START34*23*43",
"START34 * 23 * 43",
"START34 * 23 * 43 *",
"START34 * 23 * 43**",
"START34 * 23 * 43* *",
})
{
auto f = data.begin(), l = data.end();
std::vector<unsigned> v;
if (parse_numbers(f, l, v)) {
std::cout << std::quoted(data) << " Parses OK: " << std::endl;
for (auto i = 0u; i < v.size(); ++i)
std::cout << i << ": " << v[i] << std::endl;
} else {
std::cout << "Parsing failed\n";
}
if (f != l) {
std::cout << "Remaining unparsed: "
<< std::quoted(std::string(f, l)) << "\n";
}
}
}
印刷品
"START34*23*43" Parses OK:
0: 52
1: 35
2: 67
"START34 * 23 * 43" Parses OK:
0: 52
1: 35
2: 67
"START34 * 23 * 43 *" Parses OK:
0: 52
1: 35
2: 67
Remaining unparsed: "*"
"START34 * 23 * 43**" Parses OK:
0: 52
1: 35
2: 67
Remaining unparsed: "**"
"START34 * 23 * 43* *" Parses OK:
0: 52
1: 35
2: 67
Remaining unparsed: "* *"
如果你真的想忽略相邻的**,但仍然继续解析,那么有用的改变是说 -qi::hex % '*'
而不是 qi::hex % '*'
这只是使 hex
可选。
#include <boost/spirit/include/qi.hpp>
#include <iomanip>
namespace qi = boost::spirit::qi;
template <typename Iterator>
bool parse_numbers(Iterator& first, Iterator last, std::vector<unsigned>& v) {
return qi::phrase_parse(first, last,
("START" >> -qi::hex % '*'), qi::space, v);
}
int main() {
for (std::string const data : {
"START34**23*43",
"START34 * 23 * 43**",
"START*******",
"START*******1 BOGUS",
})
{
auto f = data.begin(), l = data.end();
std::vector<unsigned> v;
if (parse_numbers(f, l, v)) {
std::cout << std::quoted(data) << " Parses OK: " << std::endl;
for (auto i = 0u; i < v.size(); ++i)
std::cout << i << ": " << v[i] << std::endl;
} else {
std::cout << "Parsing failed\n";
}
if (f != l) {
std::cout << "Remaining unparsed: "
<< std::quoted(std::string(f, l)) << "\n";
}
}
}
印刷品
"START34**23*43" Parses OK:
0: 52
1: 35
2: 67
"START34 * 23 * 43**" Parses OK:
0: 52
1: 35
2: 67
"START*******" Parses OK:
"START*******1 BOGUS" Parses OK:
0: 1
Remaining unparsed: "BOGUS"
在这种情况下,你可能想重新确认所有输入都是用
>> qi::eoi
(这比手动检查迭代器要好),见 活在科利鲁:"START34**23*43" OK: 0: 52 1: 35 2: 67 "START34 * 23 * 43**" OK: 0: 52 1: 35 2: 67 "START*******" OK: "START*******1 BOGUS" Failed
对于您更新的问题 评论:
@sehe 所以像这样: coliru.stacked-crooked.coma5ecc5462a8dc0081 -----------。用户3314011 19分钟前
你需要一个消极的展望来排除。**
:
"START" >> (qi::hex % (qi::lit('*') - "**")) >> "**"
其实,让我们增加一些期待点(>
而不是 >>
):
try {
return qi::parse(first, last, "START" > (qi::hex % (qi::lit('*') - "**")) > "**" > qi::eoi, v);
} catch (qi::expectation_failure<Iterator> const& ef) {
std::ostringstream msg;
msg << "Expected " << ef.what_ << " at " << std::quoted(std::string(ef.first, ef.last), '\'');
throw ParseError(msg.str());
}
现在你也可以得到一些像样的错误信息了:
#include <boost/spirit/include/qi.hpp>
#include <iomanip>
namespace qi = boost::spirit::qi;
struct ParseError : std::runtime_error {
ParseError(std::string msg) : std::runtime_error(std::move(msg)) {}
};
template <typename Iterator>
bool parse_numbers(Iterator& first, Iterator last, std::vector<unsigned>& v) {
try {
return qi::parse(first, last, "START" > (qi::hex % (qi::lit('*') - "**")) > "**" > qi::eoi, v);
} catch (qi::expectation_failure<Iterator> const& ef) {
std::ostringstream msg;
msg << "Expected " << ef.what_ << " at " << std::quoted(std::string(ef.first, ef.last), '\'');
throw ParseError(msg.str());
}
}
int main() {
for (std::string const data : {
"START34*23*43", // Fail no EOM
"START34 * 23 * 43", // Fail spaces
"START34*23*43*", // Fail no EOM
"START34*23*43**", // OK
"START34*23*43**1", // Fail extra number
})
{
std::cout << std::quoted(data) << " -> ";
auto f = data.begin(), l = data.end();
std::vector<unsigned> v;
try {
if (parse_numbers(f, l, v)) {
std::cout << " OK:";
for (auto i : v)
std::cout << " " << i;
std::cout << "\n";
} else {
std::cout << "Not matched\n";
}
} catch(ParseError const& pe) {
std::cout << "Error: " << pe.what() << "\n";
}
}
}
印刷:
"START34*23*43" -> Error: Expected "**" at ''
"START34 * 23 * 43" -> Error: Expected "**" at ' * 23 * 43'
"START34*23*43*" -> Error: Expected "**" at '*'
"START34*23*43**" -> OK: 52 35 67
"START34*23*43**1" -> Error: Expected <eoi> at '1'