[escapeXml] escape XML special chars

escapeXml.cpp

#include <iostream>
#include <string>
using namespace std;

std::string escapeXml(const std::string& s) {
    std::string ret;
    std::string::size_type i = 0;
    std::string::size_type pos = 0;
    for (; i != s.size(); ++i) {
        std::string rep;
        if (s[i] == '<') {
            rep = "&lt;";
        } else if (s[i] == '>') {
            rep = "&gt;";
        } else if (s[i] == '&') {
            rep = "&amp;";
        } else {
            continue;
        }

        ret += s.substr(pos, i - pos) + rep;
        pos = i + 1;
    }

    ret += s.substr(pos);
    return ret;
}

std::string unescapeXml(const std::string& s) {
    std::string ret;
    std::string::size_type i = 0;
    std::string::size_type pos = 0;
    while (i < s.size()) {
        std::string rep;
        if (s[i] == '&') {
            if (s.substr(i, 4) == "&lt;") {
                ret += s.substr(pos, i - pos) + "<";
                i += 4;
                pos = i;
            } else if (s.substr(i, 4) == "&gt;") {
                ret += s.substr(pos, i - pos) + ">";
                i += 4;
                pos = i;
            } else if (s.substr(i, 5) == "&amp;") {
                ret += s.substr(pos, i - pos) + "&";
                i += 5;
                pos = i;
            } else {
                ++i;
            }
        } else {
            ++i;
        }
    }

    ret += s.substr(pos);
    return ret;
}


int main() {
    std::string ss("[hello xml] < '500' && [xml hello] > '100'");
    cout << escapeXml(ss) << endl;

    std::string xx("[hello xml] &lt; '500' &amp;&amp; [xml hello] &gt; '100'");
    cout << unescapeXml(xx) << endl;
}