Stuck with boost::xpressives $1 and using it

[ih8censorship]

What my code does is check its input for characters that should be escaped as hex characters in an output file. The problem comes with replacing the literal character with an escaped version, I passed $1 to a function but it was literally $1 instead of the characters I was hoping it would be. I'm trying to figure out how I can take the value my regex matched and replace the literal value with the escaped hex value. Any ideas?

Code

GeSHi (cpp):
#include <boost/xpressive/xpressive.hpp>
#include <iostream>
#include <sstream>
using namespace std;
using namespace boost::xpressive;
 
 
string bar(string foo)
{
 stringstream sstream;
 sstream<<"\\x"<<std::hex<<(int)foo[0];
 return sstream.str();
}
 
int main()
{
     string indata="\x42\x01\x20\x21\x02\x03-";
     sregex escseq = sregex::compile("([^\\x20-\\x7D])");
     string::iterator it=indata.begin();
     cout<<regex_replace( indata, escseq, bar("$1") );
     cin.get();
 
     return 0;
}
Created by GeSHI 1.0.7.18

[adeyblue]

You mean something like this?

Code

GeSHi (cpp):
// everything else as it was
cout << regex_replace( indata, escseq, "\\x$1");
 
Created by GeSHI 1.0.7.18

I'm not sure you can replace the matched char with it's ascii value just using strings. The xpressive string substitution page suggests that this would be more inline with what you want:

Code

GeSHi (cpp):
#include <boost/xpressive/regex_constants.hpp>
#include <iostream>
#include <sstream>
using namespace std;
using namespace boost::xpressive;
 
std::string escaper(const smatch &what)
{
    std::stringstream stream("\\x");
    stream << std::hex << (int)what[1].str()[0];
    return stream.str();
}
 
int main()
{
    string indata="\x42\x01\x20\x21\x02\x03-";
    sregex escseq = sregex::compile("([^\\x20-\\x7D])");
    cout << regex_replace( indata, escseq, escaper);
    cin.get();
    return 0;
}
 
Created by GeSHI 1.0.7.18

But I don't have 1.36 installed at the mo so I can't test it

[ih8censorship]

Thanks, that helped a lot  this is what i wound up with:

Code

GeSHi (cpp):
#include <sstream>
#include <iostream>
#include <boost/xpressive/xpressive.hpp>
using namespace boost;
using namespace xpressive;
 
 
 
std::string escaper(const smatch &what)
{
    std::stringstream stream;
    int charvalue=(int)what[1].str()[0];
     if(charvalue<=16)
     {
      stream <<"\\x"<<'0'<<std::hex << charvalue;
     }
     else
     {
      stream <<"\\x"<<std::hex << charvalue;
     }
    return stream.str();
}
 
int main()
{
    std::string indata="\x42\x01\x20\x21\x02\x03-";
    sregex escseq = sregex::compile("([^\\x20-\\x7D])");
    std::cout << regex_replace( indata, escseq, escaper);
    std::cin.get();
    return 0;
}
 
Created by GeSHI 1.0.7.18