#include<iostream>
#include<string>
#include<stdio.h>
#include<assert.h>
#include<fstream>
using namespace std;

unsigned char ToHex(unsigned char x)
{
	return  x > 9 ? x + 55 : x + 48;
}

unsigned char FromHex(unsigned char x)
{
	unsigned char y;
	if (x >= 'A' && x <= 'Z') y = x - 'A' + 10;
	else if (x >= 'a' && x <= 'z') y = x - 'a' + 10;
	else if (x >= '0' && x <= '9') y = x - '0';
	else assert(0);
	return y;
}

std::string UrlEncode(const std::string& str)
{
	std::string strTemp = "";
	size_t length = str.length();
	for (size_t i = 0; i < length; i++)
	{
		if (isalnum((unsigned char)str[i]) ||
			(str[i] == '-') ||
			(str[i] == '_') ||
			(str[i] == '.') ||
			(str[i] == '~'))
			strTemp += str[i];
		else if (str[i] == ' ')
			strTemp += "+";
		else
		{
			strTemp += '%';
			strTemp += ToHex((unsigned char)str[i] >> 4);
			strTemp += ToHex((unsigned char)str[i] % 16);
		}
	}
	return strTemp;
}

std::string UrlDecode(const std::string& str)
{
	std::string strTemp = "";
	size_t length = str.length();
	for (size_t i = 0; i < length; i++)
	{
		if (str[i] == '+') strTemp += ' ';
		else if (str[i] == '%')
		{
			assert(i + 2 < length);
			unsigned char high = FromHex((unsigned char)str[++i]);
			unsigned char low = FromHex((unsigned char)str[++i]);
			strTemp += high * 16 + low;
		}
		else strTemp += str[i];
	}
	return strTemp;
}

int main()
{
	//进行URL编码 纯英文 对于不带中文的字符转的码ansi和utf8是一样的
	string str1 = "=;+/,";
	string str1_url = UrlEncode(str1);
	cout << str1_url << endl;

	//对于带中文的ansi 编码和解码 
	string str_ansi = "还魂草";
	string str_ansi_en = UrlEncode(str_ansi);
	cout << str_ansi_en << endl;

	//ansi的中文解码后也是ansi格式的中文
	string str_ansi_de = UrlDecode(str_ansi_en);
	cout << str_ansi_de << endl;

	//对于带中文的utf8的编码和解码
	string str_utf8 = u8"还魂草";
	string str_utf8_en = UrlEncode(str_utf8);
	//可以看到相同的中文 utf8和ansi是不一样的
	cout << str_utf8_en << endl;

	//utf8的中文解码后也是utf8的
	string str_utf8_de = UrlDecode(str_utf8_en);
	cout << str_utf8_de << endl;
	ofstream wtxt("log.txt");
	wtxt << str_utf8_de << endl;
	wtxt.close();


	getchar();
	return 0;
}

以上程序执行的结果如下：

%3D%3B%2B%2F%2C
%BB%B9%BB%EA%B2%DD
还魂草
%E8%BF%98%E9%AD%82%E8%8D%89
杩橀瓊鑽

因为在C++控制台直接输出的为ansi格式字符串才不会乱码，因此最后一行的解密出的还魂草为utf8，直接输出为乱码，不过可以从log.txt中查看，打开log.txt，可以看到解密出的字符串并且编码格式为utf8