[I am using Boost 1.35, on Linux, running gcc 4.1.2]
I want to parse a string like the following
---
ResA { opt1=>val1, opt2 => val2}, ResB
ResC {opt3=> valllll }
ResD
---
I thought that maybe it is easier to to this using xpressive rather than
Spirit (which I have used for more complicated stuff so far).
I am happy to say, that with the very helpful docs I was able to create a
sregex that parses the above. Also, I found it the solution is quite short,
so I am basically happy with xpressive.
As this was my first try, there is certainly (lots of) room for improvement:
I have attached my program, and would welcome comments (and suggestions for
enhancements.)
#include
#include
using namespace boost::xpressive;
using namespace std;
#include
#include <iostream>
#include <map>
int main(int, char **)
{
string input =
"ResA { opt1=>val1, opt2 => val2}, ResB\n"
" ResC {opt3=> valllll }\n\n\n"
"ResD";
typedef map options_t;
typedef map resources_t;
resources_t result;
// The name of the resource we are parsing now.
string res_name;
// Pointer to options (map) of the resource we are parsing now.
options_t *optsref;
// Match an option(name) and its value. Both strings,
// separated by =>, and then stuff the result into the
// options-map of the resource we are parsing now.
sregex rx_opt = ( (s1= +_w) >> *_s >> "=>" >> *_s >> (s2= +_w) )
[ (*ref(optsref)) [s1] = s2 ];
// A resource has a name and, enclosed in {}, option=>name
// pairs. We store the name of the resource and the address
// of its options map.
sregex rx_res =
*_s
>> (s1= +_w)[ref(res_name)=s1, ref(optsref)=&(ref(result)[s1])]
>> *_s
>> optional( '{' >> *_s >> rx_opt
>> *(*_s >> ',' >> *_s >> rx_opt)
>> *_s >> '}' >> *_s);
// A line may contains comma separated resource definitions.
sregex rx_line = rx_res >> * (*_s >> ',' >> *_s >> rx_res);
// A file consists of multiple lines.
sregex rx_file = rx_line >> *(*_n >> rx_line) >> *_n;
if(regex_match(input, rx_file))
{
// output the parsed structure.
cerr << "resname="< " << o.second << endl;
}
}
else
cerr << "NO MATCH!" << endl;
return 0;
}
In particular, I'd like to know:
1) Is it possible to avoid my (ugly) use of "*optsref"?
I would have liked to write something like
sregex rx_opt = ( (s1= +_w) >> *_s >> "=>" >> *_s >> (s2= +_w) )
[ (ref(result[ref(res_name)])) [s1] = s2 ];
ie nest the maps directly. The way I tried, it would not compile.
2) Can I tell xpressive to allow arbitrary whitespace around ">>"?
I'd rather avoid cluttering the regexes with all that ">> *_s".
3) If the string does *not* match the sregex, can I find out where the
failure occured (ie what is the length of the prefix that could have been
completed to a succesful match.)?
Thank you and best regards, keep up the good work,
Christoph
