C/C++ URLEncode

urlEncodeCPP

#include <stdlib.h>
#include <string.h>
#include <stdio.h>
#include <iostream>
#include <vector>

void hexchar(unsigned char c, unsigned char &hex1, unsigned char &hex2)
{
    hex1 = c / 16;
    hex2 = c % 16;
    hex1 += hex1 <= 9 ? '0' : 'a' - 10;
    hex2 += hex2 <= 9 ? '0' : 'a' - 10;
}

std::string urlEncodeCPP(std::string s)
{
    const char *str = s.c_str();
    std::vector<char> v(s.size());
    v.clear();
    for (size_t i = 0, l = s.size(); i < l; i++)
    {
        char c = str[i];
        if ((c >= '0' && c <= '9') ||
            (c >= 'A' && c <= 'Z') ||
            (c >= 'a' && c <= 'z') ||
            c == '-' || c == '_' || c == '.' || c == '!' || c == '~' ||
            c == '*' || c == '\'' || c == '(' || c == ')')
        {
            v.push_back(c);
        }
        else if (c == ' ')
        {
            v.push_back('+');
        }
        else
        {
            v.push_back('%');
            unsigned char d1, d2;
            hexchar(c, d1, d2);
            v.push_back(d1);
            v.push_back(d2);
        }
    }
    
    return std::string(v.cbegin(), v.cend());
}