Base64转换的代码。

不解释。

staticchar base64EncodingTable[64] = {

'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P',

'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', 'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f',

'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', 'o', 'p', 'q', 'r', 's', 't', 'u', 'v',

'w', 'x', 'y', 'z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '+', '/'

};

+ (NSString *) base64StringFromData: (NSData *)data length: (int)length {

unsignedlong ixtext, lentext;

long ctremaining;

unsignedchar input[3], output[4];

short i, charsonline = 0, ctcopy;

constunsigned char *raw;

NSMutableString *result;

lentext = [data length]; 

if (lentext < 1)

return@"";

result = [NSMutableString stringWithCapacity: lentext];

raw = [data bytes];

ixtext = 0; 

while (true) {

ctremaining = lentext - ixtext;

if (ctremaining <= 0) 

break;        

for (i = 0; i < 3; i++) { 

unsignedlong ix = ixtext + i;

if (ix < lentext)

input[i] = raw[ix];

else

input[i] = 0;

}

output[0] = (input[0] & 0xFC) >> 2;

output[1] = ((input[0] & 0x03) << 4) | ((input[1] & 0xF0) >> 4);

output[2] = ((input[1] & 0x0F) << 2) | ((input[2] & 0xC0) >> 6);

output[3] = input[2] & 0x3F;

ctcopy = 4;

switch (ctremaining) {

case 1: 

ctcopy = 2; 

break;

case 2: 

ctcopy = 3; 

break;

}

for (i = 0; i < ctcopy; i++)

[result appendString: [NSString stringWithFormat:@"%c", base64EncodingTable[output[i]]]];

for (i = ctcopy; i < 4; i++)

[result appendString:@"="];

ixtext += 3;

charsonline += 4;

if ((length > 0) && (charsonline >= length))

charsonline = 0;

}

return result;

}