参考http://www.2cto.com/kf/201111/112519.html
亲测，可用，就是返回值直接返回std::string效率不高。
const static class CConvert{
public:
static void _enBase64Help(unsigned char chasc[3],unsigned char chuue[4]);
static void _deBase64Help(unsigned char chuue[4],unsigned char chasc[3]);
static string enBase64( const char* inbuf, size_t inbufLen );
static string enBase64( const string &inbuf);
static int deBase64( string src, char* outbuf );
static string deBase64( string src);
};
void CConvert::_enBase64Help(unsigned char chasc[3],unsigned char chuue[4])
{
int i, k=2;
unsigned char t = 0;
for(i=0; i<3; i++)
{
*(chuue+i) = *(chasc+i)>>k;
*(chuue+i) |= t;
t = *(chasc+i)<<(8-k);
t >>= 2;
k += 2;
}
*(chuue+3) = *(chasc+2)&63;
for ( i=0; i<4; i++ ) {
if ( (*(chuue+i)<=128) && (*(chuue+i)<=25) ) {
*(chuue+i) += 65; // 'A'-'Z'
} else if ( (*(chuue+i)>=26) && (*(chuue+i)<=51) ) {
*(chuue+i) += 71; // 'a'-'z'
} else if ( (*(chuue+i)>=52) && (*(chuue+i)<=61) ) {
*(chuue+i) -= 4; // 0-9
} else if ( *(chuue+i)==62 ) {
*(chuue+i) = 43; // +
} else if ( *(chuue+i)==63 ) {
*(chuue+i) = 47; // /
}
}
}
void CConvert::_deBase64Help(unsigned char chuue[4],unsigned char chasc[3]) {
int i,k=2;
unsigned char t=0;
for( i=0; i<4; i++) {
if ( (*(chuue+i)>=65) && (*(chuue+i)<=90))
*(chuue+i) -= 65; // 'A'-'Z' -> 0-25
else if ( (*(chuue+i)>=97)&&(*(chuue+i)<=122) )
*(chuue+i) -= 71; // 'a'-'z' -> 26-51
else if ( (*(chuue+i)>=48)&&(*(chuue+i)<=57) )
*(chuue+i) += 4; // '0'-'9' -> 52-61
else if ( *(chuue+i)==43 )
*(chuue+i) = 62; // + -> 62
else if ( *(chuue+i)==47 )
*(chuue+i) = 63; // / -> 63
else if ( *(chuue+i)==61 )
*(chuue+i) = 0; // = -> 0 Note: 'A'和'='都对应了0
}
for ( i=0; i<3; i++ ) {
*(chasc+i) = *(chuue+i) << k;
k += 2;
t = *(chuue+i+1) >> (8-k);
*(chasc+i) |= t;
}
}
string CConvert::enBase64( const char* inbuf, size_t inbufLen ) {
string outStr;
unsigned char in[8];
unsigned char out[8];
out[4] = 0;
size_t blocks = inbufLen / 3;
for ( size_t i=0; i<blocks; i++ ) {
in[0] = inbuf[i*3];
in[1] = inbuf[i*3+1];
in[2] = inbuf[i*3+2];
_enBase64Help(in,out);
outStr += out[0];
outStr += out[1];
outStr += out[2];
outStr += out[3];
}
if ( inbufLen % 3 == 1 ) {
in[0] = inbuf[inbufLen-1];
in[1] = 0;
in[2] = 0;
_enBase64Help(in,out);
outStr += out[0];
outStr += out[1];
outStr += '=';
outStr += '=';
} else if ( inbufLen % 3 == 2 ) {
in[0] = inbuf[inbufLen-2];
in[1] = inbuf[inbufLen-1];
in[2] = 0;
_enBase64Help(in,out);
outStr += out[0];
outStr += out[1];
outStr += out[2];
outStr += '=';
}
return string(outStr);
}
string CConvert::enBase64( const string &inbuf)
{
return CConvert::enBase64( inbuf.c_str(), inbuf.size() );
}
int CConvert::deBase64( string src, char* outbuf ) {
// Break when the incoming base64 coding is wrong
if((src.size() % 4 )!= 0 )
{
return 0;
}
unsigned char in[4];
unsigned char out[3];
size_t blocks = src.size()/4;
for ( size_t i=0; i<blocks; i++ ) {
in[0] = src[i*4];
in[1] = src[i*4+1];
in[2] = src[i*4+2];
in[3] = src[i*4+3];
_deBase64Help(in,out);
outbuf[i*3] = out[0];
outbuf[i*3+1] = out[1];
outbuf[i*3+2] = out[2];
}
int length = src.size() / 4 * 3;
if ( src[src.size()-1] == '=' ) {
length--;
if ( src[src.size()-2] == '=' ) {
length--;
}
}
return length;
}
string CConvert::deBase64( string src)
{
char * buf=new char[src.length()*2];
int len=deBase64(src,buf);
buf[len]='\0';
string result=string(buf,len);
delete [] buf;
return result;
}