同系列文章：
Base64.h
/* ----------------------------------------------------------
* 文件名称：Base64.h
*
* 作者：秦建辉
*
* MSN：splashcn@msn.com
* QQ：36748897
*
* 博客：http://www.firstsolver.com/wordpress/
*
* 开发环境：
* Qt Creator 2.6.0
* Qt Library 4.8.4
* Ubuntu 12.10
*
* 版本历史：
* V1.0 2012年12月07日
* 实现Base64编解码
------------------------------------------------------------ */
#ifndef BASE64_H
#define BASE64_H
#include <QString>
class Base64
{
public:
/*
* 功能：静态成员函数，将字节数组转换为Base64编码字符串
* 参数说明：
* binaryData：要转换的字节数组
* 返回值：
* 转换后得到的Base64编码字符串
* 异常抛出：
* 无
* 说明：
* 空说明列表指出函数不抛出任何异常
* 如果一个函数声明没有指定异常说明，则该函数可以抛出任意类型的异常
*/
static QString encode(const QByteArray & binaryData) throw();
/*
* 功能：静态成员函数，将Base64编码字符串解码为字节数组
* 参数说明：
* base64String：要转换的Base64编码字符串
* 返回值：
* 解码后得到的字节数组
* 异常抛出：
* 抛出整型异常
* -1：数据错误
* 说明：
* 字符串中允许任意的空白字符、回车换行符、连字符
*/
static QByteArray decode(const QString & base64String) throw(int);
};
#endif // BASE64_H
Base64.cpp
#include "Base64.h"
#include <QDataStream>
static const char* DATA_BIN2ASCII = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
// Base64编码，该函数不抛出任何异常
QString Base64::encode(const QByteArray & binaryData) throw()
{
if(binaryData.isEmpty())return QString();
QString sb;
int index = 0;
for(int i = binaryData.length(); i > 0; i -= 3)
{ // 将3字节数据转换成4个ASCII字符
if(i >= 3)
{
int b0 = binaryData[index++] & 0xFF;
int b1 = binaryData[index++] & 0xFF;
int b2 = binaryData[index++] & 0xFF;
sb.append(DATA_BIN2ASCII[b0 >> 2]);
sb.append(DATA_BIN2ASCII[((b0 << 4) | (b1 >> 4)) & 0x3F]);
sb.append(DATA_BIN2ASCII[((b1 << 2) | (b2 >> 6)) & 0x3F]);
sb.append(DATA_BIN2ASCII[b2 & 0x3F]);
}
else
{
int b0 = binaryData[index++] & 0xFF;
int b1;
if(i == 2)
b1 = binaryData[index++] & 0xFF;
else
b1 = 0;
sb.append(DATA_BIN2ASCII[b0 >> 2]);
sb.append(DATA_BIN2ASCII[((b0 << 4) | (b1 >> 4)) & 0x3F]);
if(i == 1)
sb.append('='); // 填充字符
else
sb.append(DATA_BIN2ASCII[(b1 << 2) & 0x3F]);
sb.append('='); // 填充字符
}
}
return sb;
}
#define B64_EOLN 0xF0 // 换行\n
#define B64_CR 0xF1 // 回车\r
#define B64_EOF 0xF2 // 连字符-
#define B64_WS 0xE0 // 跳格或者空格（\t、space）
#define B64_ERROR 0xFF // 错误字符
#define B64_NOT_BASE64 0xF3 // 空白字符、回车换行字符、连字符
static const quint8 DATA_ASCII2BIN[128] = {
0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xE0,0xF0,0xFF,0xFF,0xF1,0xFF,0xFF,
0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,
0xE0,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0xFF,0x3E,0xFF,0xF2,0xFF,0x3F,
0x34,0x35,0x36,0x37,0x38,0x39,0x3A,0x3B,0x3C,0x3D,0xFF,0xFF,0xFF,0x00,0xFF,0xFF,
0xFF,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0A,0x0B,0x0C,0x0D,0x0E,
0x0F,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0xFF,0xFF,0xFF,0xFF,0xFF,
0xFF,0x1A,0x1B,0x1C,0x1D,0x1E,0x1F,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28,
0x29,0x2A,0x2B,0x2C,0x2D,0x2E,0x2F,0x30,0x31,0x32,0x33,0xFF,0xFF,0xFF,0xFF,0xFF
};
// Base64解码，该函数抛出整型异常
QByteArray Base64::decode(const QString & base64String) throw(int)
{
if(base64String.isEmpty()) return QByteArray();
int length = base64String.length(); // 字符串长度
QByteArray ba; // 字节数组
QDataStream out(&ba, QIODevice::WriteOnly); // 写入数据流
int index = 0;
int previous = 0;
for(int i = 0; i < length; i++)
{
int charValue = base64String[i].unicode(); // 字符的Unicode编码
if(charValue >= 0x80) throw(-1); // 数据错误
int orderValue = DATA_ASCII2BIN[charValue];
if(orderValue == B64_ERROR) throw(-1); // 数据错误
// 跳过空白字符、回车换行字符、连字符
if((orderValue | 0x13) == B64_NOT_BASE64)
continue;
if(index == 0)
{
if(charValue == '=') throw(-1); // 数据错误
previous = orderValue;
index++;
}
else if(index == 1)
{
if(charValue == '=') throw(-1); // 数据错误
out << static_cast<quint8>((previous << 2) | (orderValue >> 4));
previous = orderValue;
index++;
}
else if(index == 2)
{
if(charValue == '=')
{ // 简化处理，不再判断第二个'='
index = 0;
break;
}
out << static_cast<quint8>((previous << 4) | (orderValue >> 2));
previous = orderValue;
index++;
}
else
{
index = 0;
if(charValue == '=')break;
out << static_cast<quint8>((previous << 6) | orderValue);
}
} // End for
if(index == 0) // 有效字符个数必须是4的倍数
return ba;
else
throw(-1); // 数据错误
}