Ausgabe:

base64: QUJDREVGR0FCQ0RFRkFCQ0RFRgZ♂È ►>Ì☺
text: ABCDEFGABCDEFABCDEF♠@L

#include <stdlib.h>
#include <string.h>
#include <iostream.h>

static unsigned char b64e[] = {
  'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', /*  0- 7 */
  'I', 'J', 'K', 'L', 'M', 'N', 'O', 'P', /*  8-15 */
  'Q', 'R', 'S', 'T', 'U', 'V', 'W', 'X', /* 16-23 */
  'Y', 'Z', 'a', 'b', 'c', 'd', 'e', 'f', /* 24-31 */
  'g', 'h', 'i', 'j', 'k', 'l', 'm', 'n', /* 32-39 */
  'o', 'p', 'q', 'r', 's', 't', 'u', 'v', /* 40-47 */
  'w', 'x', 'y', 'z', '0', '1', '2', '3', /* 48-55 */
  '4', '5', '6', '7', '8', '9', '+', '/'  /* 56-63 */
};

static unsigned char b64d[] = {
  0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, /* 0x00-0x0F */
  0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00, /* 0x10-0x1F */
  0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x00,0x3e,0x00,0x00,0x00,0x3f, /* 0x20-0x2F */
  0x34,0x35,0x36,0x37,0x38,0x39,0x3a,0x3b,0x3c,0x3d,0x00,0x00,0x00,0x00,0x00,0x00, /* 0x30-0x3F */
  0x00,0x00,0x01,0x02,0x03,0x04,0x05,0x06,0x07,0x08,0x09,0x0a,0x0b,0x0c,0x0d,0x0e, /* 0x40-0x4F */
  0x0f,0x10,0x11,0x12,0x13,0x14,0x15,0x16,0x17,0x18,0x19,0x00,0x00,0x00,0x00,0x00, /* 0x50-0x5F */
  0x00,0x1a,0x1b,0x1c,0x1d,0x1e,0x1f,0x20,0x21,0x22,0x23,0x24,0x25,0x26,0x27,0x28, /* 0x60-0x6F */
  0x29,0x2a,0x2b,0x2c,0x2d,0x2e,0x2f,0x30,0x31,0x32,0x33,0x00,0x00,0x00,0x00,0x00  /* 0x70-0x7F */
};

void b64encode(unsigned char *in, unsigned char *out)
{
  int inlen = strlen(in);
  while (inlen > 0) {
    unsigned char t0 = (inlen > 0) ? in[0] : 0;
    unsigned char t1 = (inlen > 1) ? in[1] : 0;
    unsigned char t2 = (inlen > 2) ? in[2] : 0;

    if (inlen <= 0) return;
    out[0] = b64e[(t0 >> 2) & 0x3f];
    out[1] = b64e[((t0 << 4) & 0x30) | (t1 >> 4)];

    if (inlen <= 1) return;
    out[2] = b64e[((t1 << 2) & 0x3c) | (t2 >> 6)];

    if (inlen <= 2) return;
    out[3] = b64e[t2 & 0x3f];
    inlen -= 3;
    in += 3;
    out += 4;
  }
}

void b64decode(unsigned char *in, unsigned char *out) {
  int inlen = strlen(in);
  while (inlen > 0) {
    unsigned char t0 = (inlen > 0) ? b64d[in[0] & 0x7f] : 0;
    unsigned char t1 = (inlen > 1) ? b64d[in[1] & 0x7f] : 0;
    unsigned char t2 = (inlen > 2) ? b64d[in[2] & 0x7f] : 0;
    unsigned char t3 = (inlen > 3) ? b64d[in[3] & 0x7f] : 0;

    if (inlen <= 0) return;
      out[0] = (t0 << 2) | (t1 >> 4);
    if (inlen <= 1) {
      out[1] = 0;
      return;
    }
    out[1] = (t1 << 4) | ((t2 & 0x3c) >> 2);
    if (inlen <= 2) {
      out[2] = 0;
      return;
    }
    out[2] = (t2 << 6) | t3;

    inlen -= 4;
    in += 4;
    out += 3;
  }
}

int main(void)
{
char in[] = {'A', 'B', 'C', 'D', 'E', 'F', 'G', 'A', 'B', 'C', 'D', 'E', 'F','A', 'B', 'C', 'D', 'E', 'F', '\0'};
char out[100];
char text[100];

b64encode(in, out);

cout << "base64: " << out << endl;

b64decode(out, text);

cout << "text: " << text << endl;
return 0;
}