网络传输文本，urlEncode和urldecode的iOS实现。

url Encode和Decode的实现

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

class UrlEncode
{
public:
    NSString* Encode(NSString*src);
    NSString* Decode(NSString* src);
private:
    string HttpUrlDecode(const string& srcUrl);
    string HttpUrlEncode(const string& srcUrl);
    int hexchar2int(char c);
    string UrlEncodeFormat(const unsigned char cValue);
    string DecimalToHexString(unsigned int nValue);

};

#include "UrlEncode.h"

NSString* UrlEncode::Encode(NSString*src)
{
    string buf = HttpUrlEncode([src UTF8String]);
    return [NSString stringWithUTF8String:buf.c_str()];
}
//
NSString* UrlEncode::Decode(NSString* src)
{
    string buf = HttpUrlDecode([src UTF8String]);
    return [NSString stringWithUTF8String:buf.c_str()];
}
//
string UrlEncode::HttpUrlDecode(const string& srcUrl)
{
    string   desStr;
	int length = 0;
	int flag      =1;
	unsigned char firstNum  = 0;
	unsigned char SecondNum = 0;
	const char * pchar = srcUrl.c_str();//.Ptr();
	while(length < srcUrl.length())
	{
		if(pchar[length]=='%')//&& length < srcUrl.length()-2
		{
			//最后一位,need break;
			if(length == srcUrl.length()-1)
			{
				desStr +=pchar[length];//.append(pchar[length]);
				break;
			}
			//正常移位
			length++;	firstNum = hexchar2int(pchar[length]);
			length++;	SecondNum = hexchar2int(pchar[length]);
            if (firstNum == -1 || SecondNum == -1)//判断字符转换成的整数是否有效
            {
                flag = 0;
                break;
            }
			desStr += char(firstNum<<4) + char(SecondNum);//.append(char(firstNum<<4) + char(SecondNum));
		}
		else if(pchar[length]=='+')
		{
			desStr +=' ';//.append(' ');//spaceb
		}
		//不是特殊字符的urlcode了，即英文字符，直接append到string即可
		else
		{
			desStr +=pchar[length];// .append(pchar[length]);
		}
		length ++;
	}
	if(flag == 0)
	{
		return srcUrl;
	}
	return desStr;
}
//
string UrlEncode::HttpUrlEncode(const string& srcUrl)
{
    string encodedUrl="";
    int length = srcUrl.length();
	if (length == 0)
	{
		return encodedUrl;
	}
	
	string sDontEncode = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789-_~.";//
    
	// Parse a the chars in the url
	for (int i=0; i<length; i++)
	{
        
		char cToFind = srcUrl.at(i);
        
		if (-1 == sDontEncode.find(cToFind,0))
		{
			// Char not found encode it.
			string tmp = UrlEncodeFormat(cToFind);
			encodedUrl.append(tmp);
		}
		else if(cToFind == ' ')
		{
			encodedUrl += '+';//.append('+');
		}
		else
		{
			encodedUrl += cToFind;//.append(&cToFind,1);
		}
	}
	return encodedUrl;
    

}
//
string UrlEncode::UrlEncodeFormat(const unsigned char cValue)
{
    string tmp;
	tmp.append("%");
	unsigned int nDiv = cValue/16;
	unsigned int nMod = cValue%16;
	tmp.append(DecimalToHexString(nDiv));
	tmp.append(DecimalToHexString(nMod));
	return tmp;
}
//
string UrlEncode::DecimalToHexString(unsigned int nValue)
{
  	string tmp;
	if(nValue<10)
		tmp+= ((char)nValue +48);//append((int)nValue);
	else
	{
		switch(nValue)
		{
                case 10:tmp.append("A");break;
                case 11:tmp.append("B");break;
                case 12:tmp.append("C");break;
                case 13:tmp.append("D");break;
                case 14:tmp.append("E");break;
                case 15:tmp.append("F");break;
                default:break;
		}
	}
	return tmp;
}
/**
 *将hex字符转换成对应的整数
 *return 0~15：转换成功，-1:表示c 不是 hexchar
 */
int UrlEncode::hexchar2int(char c)
{
    if (c >= '0' && c <= '9')
        return c - '0';
    else if (c >= 'a' && c <= 'f')
        return c - 'a' + 10;
    else if (c >= 'A' && c <= 'F')
        return c - 'A' + 10;
    else
        return -1;
}