Windows API base64 encode/decod - c++

Question

I want to base64 a big file (500MB)
I use this code but it doesn't work for a large file
I test CryptStringToBinary but it doesn't work too
what should I do????

Answer 1

The issue is clearly that there is not enough memory to store a 500 megabyte string in a 32-bit application.
The one solution is alluded to by the this link, which writes the data to a string. Assuming that the code works correctly, it is not that hard to adjust it to write to a file stream.
#include <windows.h>
#include <fstream>
static const wchar_t *Base64Digits = L"ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/";
int Base64Encode(const BYTE* pSrc, int nLenSrc, std::wostream& pDstStrm, int nLenDst)
{
wchar_t pDst[4];
int nLenOut = 0;
while (nLenSrc > 0) {
if (nLenDst < 4) return(0);
int len = 0;
BYTE s1 = pSrc[len++];
BYTE s2 = (nLenSrc > 1) ? pSrc[len++] : 0;
BYTE s3 = (nLenSrc > 2) ? pSrc[len++] : 0;
pSrc += len;
nLenSrc -= len;
//------------------ lookup the right digits for output
pDst[0] = Base64Digits[(s1 >> 2) & 0x3F];
pDst[1] = Base64Digits[(((s1 & 0x3) << 4) | ((s2 >> 4) & 0xF)) & 0x3F];
pDst[2] = Base64Digits[(((s2 & 0xF) << 2) | ((s3 >> 6) & 0x3)) & 0x3F];
pDst[3] = Base64Digits[s3 & 0x3F];
//--------- end of input handling
if (len < 3) { // less than 24 src bits encoded, pad with '='
pDst[3] = L'=';
if (len == 1)
pDst[2] = L'=';
}
nLenOut += 4;
// write the data to a file
pDstStrm.write(pDst,4);
nLenDst -= 4;
}
if (nLenDst > 0) *pDst = 0;
return (nLenOut);
}
The only changes done were to write the 4 bytes to a wide stream instead of appending the data to a string
Here is an example call:
int main()
{
std::wofstream ofs(L"testfile.out");
Base64Encode((BYTE*)"This is a test", strlen("This is a test"), ofs, 1000);
}
The above produces a file with the base64 string VGhpcyBpcyBhIHRlc3Q=, which when decoded, produces This is a test.
Note that the parameter is std::wostream, which means any wide output stream class (such as std::wostringstream) will work also.