How Can I Decode Base64 Strings in C ?

Decoding Base64 in C

Many of us, at some point in time, have stumbled upon a file or string encoded with Base64 and have no idea where to start. In such cases, it helps to have a working C code snippet for decoding such messages.

René Nyffenegger wrote an implementation that takes a binary data pointer and its size, and converts the raw data into a std::string with the corresponding Base64 encoded data. The provided solution includes a header file (base64.h) and a source file (base64.cpp).

Below is the optimized base64.h header file:

#ifndef _BASE64_H_
#define _BASE64_H_

#include <vector>
#include <string>
typedef unsigned char BYTE;

std::string base64_encode(BYTE const* buf, unsigned int bufLen);
std::vector<byte> base64_decode(std::string const&);

#endif</byte></string></vector>

And here's the modified base64.cpp source file:

#include "base64.h"
#include <iostream>

static const std::string base64_chars =
             "ABCDEFGHIJKLMNOPQRSTUVWXYZ"
             "abcdefghijklmnopqrstuvwxyz"
             "0123456789+/";


static inline bool is_base64(BYTE c) {
  return (isalnum(c) || (c == '+') || (c == '/'));
}

std::string base64_encode(BYTE const* buf, unsigned int bufLen) {
  std::string ret;
  int i = 0;
  int j = 0;
  BYTE char_array_3[3];
  BYTE char_array_4[4];

  while (bufLen--) {
    char_array_3[i++] = *(buf++);
    if (i == 3) {
      char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
      char_array_4[1] = ((char_array_3[0] & 0x03) > 4);
      char_array_4[2] = ((char_array_3[1] & 0x0f) > 6);
      char_array_4[3] = char_array_3[2] & 0x3f;

      for(i = 0; (i ';

    char_array_4[0] = (char_array_3[0] & 0xfc) >> 2;
    char_array_4[1] = ((char_array_3[0] & 0x03) > 4);
    char_array_4[2] = ((char_array_3[1] & 0x0f) > 6);
    char_array_4[3] = char_array_3[2] & 0x3f;

    for (j = 0; (j  base64_decode(std::string const& encoded_string) {
  int in_len = encoded_string.size();
  int i = 0;
  int j = 0;
  int in_ = 0;
  BYTE char_array_4[4], char_array_3[3];
  std::vector<byte> ret;

  while (in_len-- && ( encoded_string[in_] != '=') && is_base64(encoded_string[in_])) {
    char_array_4[i++] = encoded_string[in_]; in_++;
    if (i ==4) {
      for (i = 0; i > 4);</byte></iostream>

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