Comment encoder et décoder de manière robuste des URL en C ?

#include <cctype>
#include <iomanip>
#include <sstream>
#include <string>

using namespace std;

string url_encode(const string &value) {
    ostringstream escaped;
    escaped.fill('0');
    escaped << hex;

    for (string::const_iterator i = value.begin(), n = value.end(); i != n; ++i) {
        string::value_type c = (*i);

        // Preserve alphanumeric and valid symbols
        if (isalnum(c) || c == '-' || c == '_' || c == '.' || c == '~') {
            escaped << c;
            continue;
        }

        // Percent-encode other characters
        escaped << uppercase;
        escaped << '%' << setw(2) << int((unsigned char) c);
        escaped << nouppercase;
    }

    return escaped.str();
}